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Username Post: Burping an engine 350 cu.in.        (Topic#348212)
rls8836 
Member
Posts: 372

Loc: North La.
Reg: 01-30-02
11-14-17 07:54 PM - Post#2714409    

How do you do this? Why would you need to do this? Have problem where my car heats up first time in the day to 220-230 and drops back down to 180 and then up again two to three times. After that it stays around 180 unless I run at a higher speed for a ways. The radiator sets in the 6 cylinder position.



 

Rick_L 
Honored Member
Posts: 27306
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-14-17 08:30 PM - Post#2714423    
    In response to rls8836

Your symptoms indicate an air or steam pocket. This causes wild indicated temperature swings during warm up.

Do you have a Vortec engine or heads?

The Vortec engines don't have an internal bypass like other SBC engines, which leads to this problem unless you install a bypass hose between the thermostat area on the intake manifold and the top of the water pump.

If it's not a Vortec, you can "burp" the cooling system by elevating the front of the car and running the engine from cold start through warm up with the radiator cap off. Actually on a trifive you shouldn't have to do this, as the top of the radiator is so far above the engine.





 
rls8836 
Member
Posts: 372

Loc: North La.
Reg: 01-30-02
11-15-17 07:20 AM - Post#2714451    
    In response to Rick_L

Rick L, no I have a stock 84 350. I had never heard of “burbing” the engine till here. I could change my thermostat I suppose and then try it again just to rule out the thermostat. My car will run warm with the original radiator that is in there, especially if I run the ac. Been fluctuating like this for many years. Owned it so long now I don’t recall doing anything to it except perhaps I may have drained and changed antifreeze before. Don’t recall that starting this fluctuation in temp. Just jack up the front end or park overnite on an incline.next morning remove the radiator cap and crank it up and run till normal operating temp. Checking the fullness of coolant and that’s it!!



 
models916 
Valued Contributor
Posts: 4774

Age: 67
Loc: Addison, IL
Reg: 05-28-10
11-15-17 09:36 AM - Post#2714478    
    In response to rls8836

Drill a tiny hole in the flat spot on the thermostat and replace it. Bleeds the air and prevents cavitation of the pump impeller.



 
rls8836 
Member
Posts: 372

Loc: North La.
Reg: 01-30-02
11-15-17 08:45 PM - Post#2714570    
    In response to models916

Models916, I don’t catch what your saying. Drill a tiny hole in the flat spot on the thermostat I get. Then “replace “ it, I don’t get. Please repeat how to go about this again because if it will work I will be grateful to you.



 
55 Shaker 
Member
Posts: 1419

Age: 68
Loc: north central IL.
Reg: 03-13-06
11-15-17 09:06 PM - Post#2714576    
    In response to rls8836

I think he means, after you drill the hole in the thermostat, then reinstall the thermostat.

The older I get, the more dangerous, I am !!!!


 
YOUNG57 
Frequent Contributor
Posts: 1021

Loc: Tennessee
Reg: 12-06-10
11-16-17 07:02 AM - Post#2714606    
    In response to Rick_L

Mine started acting that way awhile back, every time I started it up cold it would heat right-up to 220⁰ plus then cool down to 180⁰ and settle there in moderate traffic. But when I got out on the interstate it would start heating up again and over heat. Turns out the thermostat was slow to open and would not open all the way. Installed another thermostat that opens sooner and farther, problem solved, now it hardly gets to 180⁰.

I put three 180⁰ Robert Shaw thermostats in a pan of water with a thermometer on the stove and watched their operations as the water heated up. I installed the one that started opening first (around 160⁰) and all the way (around 200⁰). They all opened and closed as water temperatures went up and down, just at different amounts and rates.

Robert Shaw thermostats (and most others) have a tiny vent hole on the edge of the valve to allow air/coolant to escape past it when closed. But I drilled three 1/16” holes around the perimeter just to speed the flow of warm coolant to it while it’s close during warm-up.



Edited by YOUNG57 on 11-16-17 07:04 AM. Reason for edit: No reason given.

 
rls8836 
Member
Posts: 372

Loc: North La.
Reg: 01-30-02
11-16-17 08:54 PM - Post#2714713    
    In response to YOUNG57

Thanks YOUNG57, I think I will try another thermastat



 
Rick_L 
Honored Member
Posts: 27306
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-16-17 09:29 PM - Post#2714717    
    In response to YOUNG57

Young57, I've had a thermostat that didn't open all the way, b it didn't have the temperature swing problem. Rather, the engine temperature operated very normally until the road speed was about 70 mph, then the temperature would start climbing in proportion to speed. Drop back below 70 mph and the temp would come back down. Maybe there would be variations in that depending on how far the thermostat opens, or whether changing engine speed could "self-close" a faulty thermostat in some circumstances.

If you have an operational internal bypass, you should not need the holes in the thermostat. But if you didn't have a proper bypass, the holes would serve that function. Thing is, too big or too many holes plus a functional bypass will mean slow warmups.

Regardless of all the above, it's all about the bypass and/or thermostat - the only two places to look.



 
YOUNG57 
Frequent Contributor
Posts: 1021

Loc: Tennessee
Reg: 12-06-10
11-19-17 09:32 PM - Post#2715014    
    In response to Rick_L

Rick L, thanks for your reply.

That’s when mine would only start over heating too, when I got on the interstate and drive at 70 mph.

I have a 1970 block and heads with a 1985 intake so the only by-pass is the third 3/8” (0.110 in ²) hole in the passenger side water pump mounting. But I don’t think it circulates much warming coolant under the thermostat but mostly prevents water pump cavitation. Warming coolant migrating up out of the heads effect the thermostat more.

I didn’t think the three 1/16” holes (0.0367 in²) I put in the thermostat would be big enough (only 1/3 the size of the 3/8” hole) to serve as coolant by-pass but just allows some warming coolant from the heads to pass by the thermostat to start opening sooner. At least that was my thinking.




 
rls8836 
Member
Posts: 372

Loc: North La.
Reg: 01-30-02
11-20-17 06:44 PM - Post#2715131    
    In response to Rick_L

RickL what is a operational bypass. I Don’t know.



 
Rick_L 
Honored Member
Posts: 27306
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-20-17 07:58 PM - Post#2715144    
    In response to rls8836

All I meant was that the engine should have the bypass holes in the water pump, block, head gasket, and head - and not be blocked by rust, sludge, etc.



 

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