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Username Post: Adding Coolant        (Topic#354127)
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
11-29-18 10:21 AM - Post#2752792    

I have a 1990 C1500 5.7 pickup. The cooling system on this truck has no bleed screw, and no valve to the heater core. I had to change a hose, and when adding coolant back I run into a confusing situation. First, with engine off, I topped off the radiator. Left the cap off and started engine. Put heat on, even though I don't think it matters since there is no heat valve so coolant is flowing through core all the time anyways. Then watched the coolant level in radiator. Once thermostat opened, the level dropped and I added more. Now the issue is that the level surges up and down in the radiator. Then when I turn the engine off it pukes out a bunch of coolant from the filler as if there was too much. Huh? So it is then left a little low so I top it off, cap it, and fill the reservoir. Drive it around, let it cool and check level. It is okay. So everything gets sorted out, but why does the level surge up and down so much at idle? With other cars, I usually just see the level stabilize, and when I shut the engine it doesn't spit out a bunch of coolant. Why on this truck? Thanks.



 
454cid 
Valued Contributor
Posts: 3026

Age: 45
Loc: West Michigan
Reg: 02-18-12
11-29-18 11:01 AM - Post#2752795    
    In response to go_hercules

Coolant expands and contracts with temperature. Also, I would expect that with the pump running the level is altered from where it would be if it were strictly subject to gravity. The truck has an overlow bottle that will be the highest point in the system. To me it sounds like you're overthinking this. Fill it up, run it, and check the level later after it's cooled. If it's not to the "cold" level in the bottle, add more.

GM's (at least older stuff) don't use bleeder screws that I've ever seen... I've never seen one on any vehicle actually.

99 K3500 RCLB


Edited by 454cid on 11-29-18 11:01 AM. Reason for edit: No reason given.

 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
11-29-18 11:15 AM - Post#2752798    
    In response to 454cid

Okay, maybe I'm not describing this just right: with the cap off and the truck idling AND thermostat open, when you look into the radiator fill hole, the coolant level goes up and down a good three to four inches. It does this rhythmically, about one surge every couple of seconds. Then when I shut it off, it pukes out a couple of cups or so of coolant. So we are not talking simple heat expansion on this scale. And the reservoir is not in play with this scenario.



 
454cid 
Valued Contributor
Posts: 3026

Age: 45
Loc: West Michigan
Reg: 02-18-12
11-29-18 11:26 AM - Post#2752799    
    In response to go_hercules

  • go_hercules Said:
Okay, maybe I'm not describing this just right: with the cap off and the truck idling AND thermostat open, when you look into the radiator fill hole, the coolant level goes up and down a good three to four inches. It does this rhythmically, about one surge every couple of seconds. Then when I shut it off, it pukes out a couple of cups or so of coolant. So we are not talking simple heat expansion on this scale. And the reservoir is not in play with this scenario.



I don't know, I've never looked at mine that closely... for one, my heater core return is right under the cap, so I can't see much with the truck running. My guess is that the thermostat is opening and closing with slight temperature changes in the system. It's not like it slams and open and slams closed, it's probably continually moving to some degree, which changes the level.


99 K3500 RCLB


 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
11-29-18 12:04 PM - Post#2752803    
    In response to 454cid

Now that's a thought. Maybe the thermostat is opening and closing, especially at idle just after coming to temperature. Now, if I can figure out how to verify that???



 
bowtie44s 
Valued Contributor
Posts: 4093
bowtie44s
Age: 35
Loc: wv
Reg: 08-29-12
11-29-18 12:13 PM - Post#2752805    
    In response to go_hercules

The cap is the highest point in the cooling system of our trucks. A bleed screw is not needed. A lot of cars have bleed screws at the highest point.

Like already stated, you're thinking too much into it. If it's killing you to know, it's expensive, but you can get this. https://coolviewthermosta t.com

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
11-29-18 03:27 PM - Post#2752823    
    In response to bowtie44s

I'm not trying to overthink it, just want to understand it and make sure it's done right. I mean if it's puking out a bunch of coolant, I'm just wondering if there is still a lot of air in the system, etc.. I think a lot of us like to understand why things happen. And like I mentioned, other cars I have had did not do this, so that's why it got my attention in the first place. Thanks.



 
454cid 
Valued Contributor
Posts: 3026

Age: 45
Loc: West Michigan
Reg: 02-18-12
11-29-18 03:47 PM - Post#2752825    
    In response to go_hercules

  • Quote:
..if it's puking out a bunch of coolant, I'm just wondering if there is still a lot of air in the system, etc..



It wouldn't puke out coolant, if you'd put the cap back on. The overflow bottle captures that coolant, and allows the air to escape the system if it's present.

Check the level in the coolant bottle over the next couple of days when cold. Maybe check the radiator after several days.


99 K3500 RCLB


Edited by 454cid on 11-29-18 04:27 PM. Reason for edit: No reason given.

 
marsmann 
Poster
Posts: 11

Reg: 10-25-18
11-29-18 08:03 PM - Post#2752849    
    In response to go_hercules

I can see why you would question this, as it is not normal behavior. Generally speaking, at warm operating temps and idle, it should not surge as violently as you describe. The theory of a thermostat opening and closing is plausible, but once warmed up it should not surge. What temp thermostat do you have in place? A standard 195 degree or cooler? And what temp does your gauge show? Check those too to help correlate this theory.

All that said, it should not fluctuate but just like the others have said simply top off your coolant, let it cycle for a bit, run the heater on high to aid in bleeding any air and you should be fine. You can optionally squeeze the lower radiator hose to aid in any bleeding if desired. The rest will cycle up to the coolant overflow bottle and bleed out if necessary.

While you had the hoses disconnected from the heater core lines, it would have been opportune to flush the system and the heater core. When doing this you can just take a garden hose and force water through the inlet line and then switch and force water backwards through the system. You'd be surprised how much gunk can come out and your heating system will run more efficiently after flushing the core.



Edited by marsmann on 11-29-18 08:08 PM. Reason for edit: No reason given.

 
wagonman100 
Super Senior Member
Posts: 14086
wagonman100
Loc: Baltimore, MD
Reg: 11-27-04
11-29-18 08:25 PM - Post#2752853    
    In response to marsmann

Yes, I flush my heater core on my new body style ‘99 Silverado at least once a year and still get gunk from general use and the Dexcool that used to reside in there.

The fluctuation you were witnessing was probably due to air in the system, maybe even in combination with the thermostat opening and closing.

Jay
Friends don’t let friends drive Fords.

1999 Silverado Z71 4X4 extra-cab short bed
1983 Malibu Fauxmad - tubbed
1978 El Camino Kustomized
1972 Monte Carlo
1957 210 handyman wagon
1957 Nomad sport wagon
1957 Cameo Carrier


 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
11-29-18 08:39 PM - Post#2752854    
    In response to wagonman100

I have the standard 195 thermostat. Changed the heater core about a year and a half ago. Like I mentioned at the top, everything is sorted out. Radiator is topped off as well as reservoir. If you re-read my initial question, I simply ask why this truck acts this way. I have never had another vehicle do this. So I understand what you guys are saying, and again everything is sorted out, I just want to know why it does this. I'm sure someone out there has seen this and figured it out.



 
TAT_2 
"17th Year" Silver Supporting Member, and Official CT Grim Reaper
Posts: 35454
TAT_2
Age: 65
Loc: "UNDER THE BOARDWALK"
Reg: 10-29-00
11-30-18 05:25 AM - Post#2752870    
    In response to go_hercules

WHEN THE THERMOSTAT FINALLY OPENS THE COOLANT FLOWS.WHEN THE THERMO CLOSES IT STOPS THE FLOW SO YOU SEE IT OVERFLOWING OUT THE RADIATOR FILL.THATS WHY WITH THE CAP OFF YOU NOTICE THE VARIATION IN THE LEVEL.THE CAP KEEPS THE PRESSURE CONSTANT.IF YA HAD A OLDER CAR/TRUCK YOU WOULD SEE HOT LEVEL,COLD LEVEL MARKED ON THE SIDE OF THE RAD.I HAD THIS PROBLEM WITH MY 68 VETTE,NO OVER FLOW TANK FROM THE FACTORY,HAD TO ADD 1 OR THE COOLANT WOULD BLOW OUT THE OVERFLOW IF I TOTALLY FILLED IT.

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go_hercules 
Poster
Posts: 89

Reg: 10-27-16
12-01-18 06:50 PM - Post#2753038    
    In response to TAT_2

Thanks for the help everyone. One final question - the overflow reservoir cap has never fit very well. The reservoir is the original GM, and I have tried an aftermarket replacement cap. When you screw it on, you have to do so carefully, a little too much and it gets loose again, like it's skipping over the plastic threads. Before swapping out to an aftermarket reservoir, is there a better cap or something I could try? Thanks.



 
CowboyTrukr 
"7th Year" Silver Supporting Member
Posts: 4093
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-01-18 10:08 PM - Post#2753053    
    In response to go_hercules

Didn’t know the ‘90 had a screw on cap. Both of mine had/have snap on caps with overflow tubes.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
12-02-18 06:00 AM - Post#2753067    
    In response to CowboyTrukr

Yeah, it has the screw-on on this 1990. Like this:

https://www.autozone.com/cooling-heating-and-c lima...

Thanks



 
someotherguy 
Senior Moderator
Posts: 28799
someotherguy
Age: 48
Loc: Texas
Reg: 08-01-03
12-02-18 06:52 AM - Post#2753072    
    In response to go_hercules

That cap isn't retaining any pressure so there's no need to screw it on tightly.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
bowtie44s 
Valued Contributor
Posts: 4093
bowtie44s
Age: 35
Loc: wv
Reg: 08-29-12
12-02-18 07:26 AM - Post#2753077    
    In response to go_hercules

My 88 is the same way. It has never fallen off so I haven't worried about it.

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Don A 
Poster
Posts: 3

Reg: 06-10-12
12-03-18 09:01 AM - Post#2753177    
    In response to go_hercules

I suspect the surge you saw at start up after the thermostat opened was a combination of the system running at or near opening and closing of the stat and the cooling system gradually re-filling the crevasse's in the water jackets in the block at idle. Because the system is a "sealed system" it will sort itself out (as you stated) after test driving and bringing the RPM's up at speed. A good way to test your overflow system would be to drive the truck or bring the RPM's up to about 2000 for a minute (200-210 degree's) and then shut the motor off and watch for the expansion in the overflow bottle. The engine coolant is now absorbing the remaining heat without moving the coolant through the radiator and due to hot coolant expansion should puke past the cap into the bottle for a period of time. At this time it will also push trapped air out into the bottle so you may see some bubbles in the expansion tank as well. To match the size of the bottle to your engine needs you can now place a box fan in front of the radiator to cool it down rapidly (which contracts the coolant as opposed to the expansion that happened when the coolant was heated) and you should see the coolant level drop in the bottle as it replaces the discharged coolant through the vacuum valve. If you don't use a box fan it could take hours for all this to happen. The important part is the capacity of the overflow bottle. If it goes empty during this process the bottle is too small for the system and will allow air to enter your cooling system and in time result in low coolant levels.



 
65_Impala 
Very Senior Member
Posts: 4139

Reg: 12-29-02
12-03-18 11:43 AM - Post#2753205    
    In response to go_hercules

I wouldn't think much of it. If you were doing it as the thermostat first opened the thermostat likely cycled open and closed a bit as it worked towards being at the correct part opening for the operating conditions.

Even with the thermostat open, revving the engine will usually show a drop in coolant. That's unless the fill cap is on the return hose tank then it'll puke a bunch of coolant. Either way, the volume observed can easily change.



 
bigalturk1 
Poster
Posts: 13

Reg: 09-20-13
12-03-18 04:13 PM - Post#2753243    
    In response to go_hercules

I always drilled a 1/8"hole in the thermostat, to bleed the system



 
go_hercules 
Poster
Posts: 89

Reg: 10-27-16
12-03-18 07:12 PM - Post#2753265    
    In response to bigalturk1

OP here: What you guys are saying makes sense. After driving several cycles, the fluid in the overflow stabilized so all is good. After looking at this for a while, I am convinced that with the upper radiator hose being the highest point in the system, there is just no way to ever get all the air out. When the radiator cap is off, as in initially filling and burping, then the cap will always be lower than the hose so no fluid could ever be in the hose with the cap off. Therefore, you can only hope that going through several drive cycles will purge air via the overflow tank. I guess if you jacked the front end high enough that might work but we are talking about 45 degrees minimum with the height of that hose.



 
G. Baker 
Poster
Posts: 34

Loc: Ontario Canada
Reg: 12-18-15
12-03-18 07:53 PM - Post#2753274    
    In response to 454cid

Just drive it and keep an eye on the level. Surging could be some trapped air but it happens in all vehicles as RPM changes or not.
My 96 Corvette LS4 had a bleeder screw at the thermostat housing. Often necessary if the heater is above top of rad. In that case it is sometimes necessary to put a piece of pipe or hose that is higher than the heater to get all the air out when filling/refilling system.



 
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