2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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05-30-08 07:47 PM - Post#1444988
Heres the set up--70 gmc with mild built 350, edelbrock intake,600 CFM carb,headers and factory air. Engine overheats at idle. Cooling system has new hoses, performance waterpump, 195 thermostat, radiator and fan shroud. Motor will warm up to 195 thermostat opens and will stay at 195 for several minutes. Temp then begins to rise fast (from 195 to 220 to 230) in a matter of 20 to 30 seconds. I thought my factory gage was malfunctioning so i put a manual water temp guage on and confirmed that the temp was rising fast. checked fan clutch for proper operation and it appears to be fine (no play, no grinding, etc.) Even if the clutch was bad I would think that the temp rise would be much slower than a 30-40 degree swing in a matter of 20-30 seconds. Checked radiator hoses while temp went up to see if they were possibly collapsing which would stop flow, but they are fine.
If i increase the RPM's to around 1500 the temp immediatle goes back down to 195 within 10 to 15 seconds. It sounds like a water flow issue at idle, but I a stumped as to where it would occur unless the water pump will not push enough flow at idle (500-600 rpm). Truck runs at about 190 on the road at 60 mph. Help!
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sgian
Valued Contributor
Posts: 4438
Loc: MO
Reg: 12-25-03
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05-30-08 08:32 PM - Post#1445020
In response to 2tone70
typically overheating at idle or low speeds but not while driving over 25 mph is an air flow problem. So following that reasoning, it is your fan clutch. Clutches will lose rpm every year, so even though there is no play or grinding it can still be worn out enough to cause the overheating. Clutches should be replaced periodically, but I don't remember how long (it's been 10 years since I worked at a parts store).
Also make sure there are no signs of leaks around the water pump body and that the water pump shaft has no play in it (belts disconnected).
Is the A/C on when it overheats? Perhaps you should unplug the A/C pump just to make sure it doesn't cycle on or something causing the overheating (like if there is an intermittent short or something causing it to cycle on and off). Turning on the older style A/C units can cause a swing like you mentioned.
| 04 Silverado Z71, 10 Cobalt |
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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05-30-08 08:53 PM - Post#1445031
In response to sgian
SGIAN,
Thanks for the reply. The AC is not operational at this time. The fan clutch is the only thing that has not been replaced. It worked fine when I took it off the truck, but it sat for 1 1/2 yrs while I did a frame off restoration. My concern was can a bad clucth make the temp rise 30 degrees or more in such a short time (from 195 to 230 in 20 to 30 seconds). I have had bad clutches before and never seen the temp rise that fast in that short of a time. The clutch is the only component of the cooling system that has not been replaced, so I guess its next.
thanks,
2tone70
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sweet70beast
Senior Member
Posts: 465
Loc: United States of Idaho
Reg: 02-12-05
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05-30-08 09:02 PM - Post#1445036
In response to 2tone70
Just wondering but, did you change the pulleys during your restoration?
70 Nova 327/T5
71 K-20 350/350/205
50 Chevy 3100
47 Chevy Panel
54 Chevy Suburban
53 GMC Suburban
76 Chev C-10 350/350
72 Skylark (Suncoupe)
1 of 3943 made
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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05-30-08 09:11 PM - Post#1445041
In response to sweet70beast
All pulleys are stock. Everything on the cooling system with the exception of the water pump is stock. The water pump is a high output pump.
thanks
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sgian
Valued Contributor
Posts: 4438
Loc: MO
Reg: 12-25-03
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05-31-08 06:02 AM - Post#1445150
In response to 2tone70
You could also try getting a block tester at Napa to check if exhaust gases are getting into the coolant once it reaches a certain temp. However, I would replace the clutch first.
Do you have an 18" fan?
Is the A/C radiator still in place? Have you made sure that no debris is blocking either radiator? You could also try removing the A/C radiator to allow more flow through the radiator.
| 04 Silverado Z71, 10 Cobalt |
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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05-31-08 11:10 AM - Post#1445305
In response to sgian
I have an 18 inch fan. The AC condensor was removed cleaned and is free of debris. I will try the clutch and see if that works. The AC switch in the cab has three vacum ports. My diagrams only indicated 2 ports. I found on the forum that a change was made in 70 and the switches had three vacum ports. I will add the additional vacum line since this could affect the heater valve connected to the heater hose. I doubt if this has much to do with the problem, but I will fix it while I am changing the clutch. We will see what happens. 
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100% CHEVY
Very Senior Member
Posts: 5437
Age: 60
Loc: Helena,Missippi,U.S.A.
Reg: 12-09-04
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05-31-08 06:33 PM - Post#1445530
In response to 2tone70
Do you have the right water pump?It could be for a serpentine belt instead of v-belt.If that's the case,it will be turning backwards and not move enough water.
Mike.
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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06-02-08 06:42 PM - Post#1447072
In response to 100% CHEVY
Put a clutch on it today. Took it out for a drive hit 195 degrees on the temp guage. All was fine for about 1 minute. Then the temp jumped to 230 in about 30 seconds and bounced between 220 and 230. I then turned on the heater and the temp dropped to 190 and frickin stayed there...I even let it sit and idle for 15 minutes and it never went above 195 with the heater on. So now Ive got to believe that the problem that I mentioned in the previous post with the AC switch and vacum lines has something to do with the problem. I will re-do the vacum lines accordfing to the diagram I found on the forum. Its to damm hot in central california in the summer to drive with the heater on!
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 JimKshortstep4x4
Chevytalk Moderator & "9th Year" Silver Supporting Member
Posts: 4163
Loc: Muskegon, MI, USA
Reg: 03-28-02
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06-03-08 06:30 AM - Post#1447330
In response to 2tone70
I don't believe that the heater has much to do with the overheating as the radiator should cool the engine by itself if it is sized right.
I have been scratching my head ever since you mentioned the problem and I believe that it is a coolant flow problem. If you have eliminated the thermostat as a problem, I would suggest getting the radiator flow tested.
Jim
Member 65-66 Full Size Chevrolet Club
65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/350
71 Snow plow, 4x4, 350, TH 350
Current project, 72 GMC Shortbed, stepside, 427 |
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Spareparts2
Senior Member
Posts: 250
Loc: Ks.
Reg: 11-17-05
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06-03-08 07:17 AM - Post#1447357
In response to JimKshortstep4x4
I think 100% Chevy has the answer, get the # off the pump and contact whoever you got it from and check if it is a serpentine pump, seen this problem before, even if it a high flow pump but turning backwards it's not going to put out much flow.
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sgian
Valued Contributor
Posts: 4438
Loc: MO
Reg: 12-25-03
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06-03-08 11:24 AM - Post#1447565
In response to Spareparts2
So it doesn't matter what speed you are driving when it runs hot? That indicates a flow problem, like mentioned. Running the heater is a bandaid that acts like an extra radiator. (Keep in mind that 230 is hot but not actually overheating. That temp in itself should not damage the engine, however it will harm the additives in the engine oil and transmission fluid and require more frequent oil changes if you want the engine and trans to last.)
Doublechecking the waterpump is not a bad idea, although I doubt it is the problem since it is not consistent and having the heater on helps (indicating there is some coolant flow). Do you still have the box or receipt so you can look up the part and make sure it isn't reverse flow? Do you know of any place that tests water pumps for flow in case it is bad?
In my experience with CA/AZ driving, just having the A/C radiator in place will raise the engine temp because it impedes airflow through the radiator. With my Nova, turning the A/C on in 100+ degree weather was a sure way to quickly raise the engine temp to the 220-230 range or higher, and those old A/C switches can be difficult to troubleshoot (I had to bypass things, add aftermarket switches, and do some rewiring for mine.)
If the A/C pump is in place and connected, you really should unplug it and see if it makes a difference because with those old switches it could be turning on under strange circumstances without you realizing it. Even if there is no refrigerant in the system, those old pumps noticeably increases engine load. It is a quick thing to check that costs you nothing, and would eliminate a possible cause.
Then I would try removing the A/C radiator if you can without damaging any lines and especially if you don't intend to fix the A/C anytime soon. That would increase air flow going through the radiator.
Now was your radiator new or rebuilt/cored? Especially if it was rebuilt, JimK's recommendation of getting it flowtested is a good idea once you have done the free steps I mentioned above with the A/C stuff.
How many cores does the radiator have? A V8 in these trucks may have come with anywhere between 2 and 4 rows (cores). Even without A/C, a 2 core is barely adequate for a V8 with an automatic in CA and AZ summers (been there, done that). Fortunately a conversion to a 4 core radiator is easy. As of about 5 years ago, a new 4 core radiator for 67-72 3/4 ton trucks was around $230, it was the stock radiator for some HD 3/4 ton applications and will still have the angled lower radiator hose fitting that is helpful. About 15 years ago when I did the conversion in CA, local junkyards had the upper mounts that will bolt right in without modification (73 and later 3/4 and heavier vans with the 4 core also have the same 4 core mount in addition to 67-72 3/4 ton and heavier trucks with 4 core radiators.)
Speaking of lower radiator hoses, did your hose have the spring in it? They used to have springs in them to prevent the hose from collapsing when the waterpump pumped more water out of the radiator, but I guess in an effort to cut costs the replacement hose makers decided it was no longer necessary. With a higher flow pump, it might be important in your application. Next time it starts running hot, take a look at that lower radiator hose and make sure it isn't getting distorted from the normal shape by the water pump's higher flow. Also make sure that any efforts to install that lower hose didn't put any kinks or restrictions in the hose (especially if you were given the 73 and later straight lower fitting instead of the angled 67-72 fitting.)
| 04 Silverado Z71, 10 Cobalt |
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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06-07-08 02:49 PM - Post#1450632
In response to sgian
 OK, Problem solved. I put a clutch on and that did not work. I then reffered to the vacum hose routing diagram I found on the forum for the AC and heater controls that hook to the AC controls in the cab. I re-routed the vacum lines according to the diagram. My AC switch has 3 ports, the manual I have only showed 2 ports so I was only using 2 of the 3 ports. Hooked ip correctly to all 3 ports. Started it up, test drove and never got over 195 degrees. I would have never of thought that the valve for the Heater core would have that much to do with the type of problem I had. Well you learn something new everyday. Thanks for all the suggestions.
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sgian
Valued Contributor
Posts: 4438
Loc: MO
Reg: 12-25-03
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06-07-08 05:22 PM - Post#1450724
In response to 2tone70
So is coolant going through the heater core all the time now? If you turn the A/C switch on, does it shut off the flow through the heater core and cause it to run hot again (have you tried it)?
| 04 Silverado Z71, 10 Cobalt |
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longhorn_man
Very Senior Member
Posts: 1931
Age: 39
Loc: Columbus Ohio
Reg: 02-02-02
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06-07-08 07:31 PM - Post#1450818
In response to sgian
I wonder if that caused a vacume leak, creating a lean condition causing the overheat.
If so, it's probably already lean.
1972 C/10 burb, 68 nose, SLAMMED... 402/TH400/3.07 <--- Chicks dig it!
1970 C/30 Longhorn, GMC nose...Caddy 425/TH350/4.10 one of 1404 built
www.longhorntrucks.freeservers.com |
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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11-21-11 04:16 PM - Post#2160442
In response to longhorn_man
I'm back again looking for more suggestions: have drove the truck occasionaly for 2 yrs with no overheating problems. Took it out the other day and turned the heater on and it began to overheat again--just like before from 190 to 230 in about 30 seconds. Shut off the heater and the temp went back down just as fast. Checked for vacum at the heater flow valve mounted on the fenderwell and it has adequate vacum. Removed the valve and inspected. was able to push valve in with screwdriver, hooked it up to hand vacum pump and it didn't move. I am going to bypass it tonight and then test the valve with the original vacum source. I will lso see if it overheats without the valve in.  I just don't understand how this valve could have that much effect on the cooling system all it does is regulate flow to the heater core, but the minute I turn the heat on the temp goes up. I drove this truck on 100+ degree days this and the temp guage never got close to hot or even midway. will see what happens tonight and then go from there. The only thing left will be the water pump if all checks out. If it is moving in the reverse direction as mentioned before I guess it could cause a problem with the heater valve. Dazed and confused
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JimKshortstep4x4
Chevytalk Moderator & "9th Year" Silver Supporting Member
Posts: 4163
Loc: Muskegon, MI, USA
Reg: 03-28-02
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11-21-11 06:01 PM - Post#2160487
In response to 2tone70
That is rather unusual. Make sure the coolant level is good as a first step!
I wonder if the heater hoses are hooked up right. On a truck with a V-8 (automatic transmission)the return hose goes to the radiator according to the assembly manual. The radiator shop where I get my work done tells me it is more important for an AC equipped truck to route the return hose to the radiator because you get better circulation.
I am not sure if your problem is caused by heater hose routing but here is an illustration from the Assembly Manual showing the different hookups.
Jim
Member 65-66 Full Size Chevrolet Club
65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/350
71 Snow plow, 4x4, 350, TH 350
Current project, 72 GMC Shortbed, stepside, 427 |
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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11-21-11 08:05 PM - Post#2160539
In response to JimKshortstep4x4
The hoses are currently routed: 5/8 supply from intake manifold toto heater valve--from heater valve to heater core. Return is 3/4 from heater core to water pump. My water pump does have a port to connect to for the supply (I have seen some diagrams that use that port). The radiator has a port near the top right side but I would need a 3/4 to 5/8 or smaller adapter to use it which I would think would restrict the flow too much.
I took the heater valve out and spliced the hoses together. The truck never got close to overheating. I then hooked up the heater valve to the vacum source to see if it opens and of course it functioned fine. Just don't get it the valve appears to work fine, but when it is installed and turned on the truck overheats almost instantly. What the hell? Guess I have no choice but to replace the valve even though it appears to function fine when vacum is applied. modified this post from original i had the routing wrong
Edited by 2tone70 on 11-21-11 08:18 PM. Reason for edit: No reason given.
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 50hotrod
"2nd Year" Silver Supporting Member
Posts: 366
Age: 56
Loc: Wisconsin
Reg: 07-25-11
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11-22-11 12:29 PM - Post#2160744
In response to 2tone70
You don't need the heater core in the system or even flow from the heater core supply lines to properly cool the engine. You can eliminate this system as the cause.
You rev the engine over 1500 RPM'S and it cools.
This tells me the radiator flow, both coolant and "air through" is good. You can eliminate the radiator as the cause.
Idle the engine with a large fan in front of the grill. This will simulate 1500 RPM air flow with the engine idling. If it still overheats on idle your clutch fan is not the problem.
If the problem was engine internal, you would have 3 things going on. Excess pressure in the radiator (head gasket leak) or water in the oil.
The third thing would be corrosion and rust in the block restricting flow. The fact that you raise the RPM'S and the temp instantly drops tells me the block is not plugged with corrosion and or rust. If it was, more RPM'S would cool more but not instantly as you stated. You can rule this out.
You never stated the radiator cap did a Kennedy space launch when you remove it so you can rule out a head gasket leak creating excess pressure in the cooling system as the cause.
Only 2 things left in the system now. The thermostat and water pump.
You have already confirmed the thermostat is good.
That leaves the water pump. Good luck.
Well, you know what's wrong with the world today
People done gone and put their Bible's away
They're living by the law of the jungle not the law of the land
"Simple Man" By Charlie Daniels
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Edited by bouncer on 11-22-11 12:38 PM. Reason for edit: No reason given.
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50hotrod
"2nd Year" Silver Supporting Member
Posts: 366
Age: 56
Loc: Wisconsin
Reg: 07-25-11
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11-22-11 01:09 PM - Post#2160754
In response to 50hotrod
P.S
I have seen NEW thermostat's act "funny".
They reach their "open" temp and suddenly "pop" open and close quickly with the slightest temperature drop.
Not saying this is your problem but always be sure your using quality replacement parts.
Well, you know what's wrong with the world today
People done gone and put their Bible's away
They're living by the law of the jungle not the law of the land
"Simple Man" By Charlie Daniels
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C10 Sleeper
Valued Contributor
Posts: 3426
Loc: Redding Ca
Reg: 03-17-09
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11-22-11 08:25 PM - Post#2160923
In response to 50hotrod
I always drill a series of small holes around the perimeter of my thermostats. Also you mentioned the motor is modified. If its been bored how much? Have you verified your timing marks are correct and the timing is not on the retarded side? Retarded timing, lean conditions and vacuum leaks cause lean conditions that can all create more heat. What does the inside of the radiator look like? Did you have a machine shop hot tank the block? There are several possibilities if you have correctly verified the obvious starting points.
Edited by C10 Sleeper on 11-22-11 08:26 PM. Reason for edit: No reason given.
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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11-26-11 03:08 PM - Post#2162056
In response to C10 Sleeper
The motor was in the truck before I bought it. I dont know what the bore is. did not have this problem before teardown. The only nmods to the motor are headers, intake and carb. I replaced the heater valve and still have the same problem. Temp stay low as long as heater is turned off or bypassed. Turn the heater on and the temp shoots up. Radiator hose has pressure so it would appear the thermostat is open. Temp at the hoses is low, I checked temps with laser thermometer. It has the stock temo guage in it, but I have verified it before by changing out with a mechanical unit. Rev up to 1500 rpms and u can visually watch temp go down. New radiator, water pump, themostat, etc. The only thing I can think of it has something to do with the vacum system, but motor runs fine when the heater is on. No water in the oil. The only thing I did notice was that the temps for the header tubes were 100 deg higher for cylinders 3 and 5 than they were for 1 and 7.
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50hotrod
"2nd Year" Silver Supporting Member
Posts: 366
Age: 56
Loc: Wisconsin
Reg: 07-25-11
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11-26-11 08:25 PM - Post#2162122
In response to 2tone70
Well, I could have told you the heater valve would not fix your problem. Did you read my last 2 posts?
The vacuum system also has nothing to do with your cooling problem.
I'm trying to keep you from wasting money on needless items and diagnose the problem through the process of elimination..... but someone will not listen.
You can not determine a thermostat is "good" by having pressure in the hoses.
Well, you know what's wrong with the world today
People done gone and put their Bible's away
They're living by the law of the jungle not the law of the land
"Simple Man" By Charlie Daniels
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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11-27-11 04:49 PM - Post#2162404
In response to 50hotrod
Yeah Bouncer I read your post. If u are so sure its the thermostat explain to me why the truck only overheats when vacum is applied to the heater valve. I left the new valve on pulled the vacum line and plugged it with the heater controls on and guess what--it doesn't overheat.
why would vacum applied to the heater valve cause the thermostat to malfunction. If I understand your theory it would be that once the heater valve is open the very slight temp difference in the return from the heater core is causing the thermostat to malfunction. now if I am somehow misunderstanding your theory please clear it up for me
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C10 Sleeper
Valued Contributor
Posts: 3426
Loc: Redding Ca
Reg: 03-17-09
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11-27-11 05:54 PM - Post#2162425
In response to 2tone70
I won't get into the above theory but I can suggest 2 simple things to probably eliminate and possibly pin point the issue. One bypass the heater core all together and test.
Two pull the thermostat and replace it or remove the center of an old one and use as a restrictor.
Do this one thing at a time and wait for results. I will put my money on the tstat or maybe even as far as the water pump if the tstat checks out as good. With all the cheap junk being made overseas and corner cutting re manufacturing companies out there its not uncommon to receive defective parts.
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64ss409
Senior Member
Posts: 602
Loc: Montana
Reg: 12-04-02
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11-27-11 06:06 PM - Post#2162432
In response to C10 Sleeper
While you are doing the above mentioned tests, remove the radiator cap and see if you can see water flow. As soon as the thermostat opens, you should be able to see water movement.
Ron
1964 SS 409/340 4 spd, bought new Oct '63
1964 Biscayne-will have 409
1962 SS convertible 4 spd 327
1971 K10 454
99 Silverado Z11
1998 C5 convertible, torch red black top |
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C10 Sleeper
Valued Contributor
Posts: 3426
Loc: Redding Ca
Reg: 03-17-09
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11-27-11 09:24 PM - Post#2162524
In response to 64ss409
Good point ron. One other thing I can suggest is jack the front of the truck up as high as safely possible and run it with the cap off. Should really help to eliminate any possible air pockets in the block, heads or intake.
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2tone70
Forum Newbie
Posts: 13
Reg: 05-30-08
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11-27-11 10:35 PM - Post#2162547
In response to C10 Sleeper
Thanks c10 and 64ss. i will proceed with your suggestions and see what happens. let you know the result when I get the time to mess with it, about a week from now.
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50hotrod
"2nd Year" Silver Supporting Member
Posts: 366
Age: 56
Loc: Wisconsin
Reg: 07-25-11
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11-28-11 09:39 AM - Post#2162617
In response to 2tone70
Yeah Bouncer I read your post. If u are so sure its the thermostat explain to me why the truck only overheats when vacum is applied to the heater valve. I left the new valve on pulled the vacum line and plugged it with the heater controls on and guess what--it doesn't overheat.
why would vacum applied to the heater valve cause the thermostat to malfunction. If I understand your theory it would be that once the heater valve is open the very slight temp difference in the return from the heater core is causing the thermostat to malfunction. now if I am somehow misunderstanding your theory please clear it up for me
QUOTE; "explain to me why the truck only overheats when vacuum is applied to the heater valve"
Apparently you have a heater control valve that is normally open and closes when vacuum is applied. Most of these valves work this way.
QUOTE; "If I understand your theory it would be that once the heater valve is open the very slight temp difference in the return from the heater core is causing the thermostat to malfunction".
Sorry for the misunderstanding. That is not what I meant. Remember, the cab heating system has nothing to do with the engine's ability to cool.
Thousands of people have re-routed and even plugged the heater lines because of leaky heater cores without any effect on engine cooling.
If you want to check your thermostat correctly, remove it. Heat a pan of water on the stove with a thermometer and the thermostat in it. When the temp reaches the thermostat temp, in this case 195, in should be already wide open. Take it off the heat and start adding cold water slowly while watching the thermometer and see when it closes. Operation should be smooth while opening and closing.
OR.....You could just spend $20.00 for a quality thermostat and gasket. That would be my first move.
Stupid question but have to ask, Are you sure the thermostat is not installed upside-down. Believe it or not but I have seen it and some thermostat housings will work with the thermostat in either way.
Well, you know what's wrong with the world today
People done gone and put their Bible's away
They're living by the law of the jungle not the law of the land
"Simple Man" By Charlie Daniels
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Magno99900
Senior Member
Posts: 641
Age: 27
Loc: Hayward, CA
Reg: 01-01-05
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11-28-11 03:22 PM - Post#2162739
In response to 50hotrod
You may wanna check that you have no vacuum leaks, as a vacuum leak would cause the motor to run lean.
Edited by Magno99900 on 11-28-11 03:22 PM. Reason for edit: No reason given.
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