burping hot engine

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Jul 17, 2005 | 11:55 AM

kessler

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Instructor

Joined: Oct 2004

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From: kill devil hills nc

burping hot engine

I have a 71 with a 350 engine. I just rebuilt the engine and it runs hot. Put a 180 degree thermostat but it seems to run real hot,,,I have heard It might be because of air in my coolant system. "burping" the system will get rid of the air and it should run cooler. Anyone ever hear of this?? If so how do you do it?? Need some help thanks

Jul 17, 2005 | 12:11 PM

Solid LT1

Le Mans Master

Joined: Dec 2003

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From: Fremont CA

You could have a problem with the cooling system not being full enough. I wouldn't "Burp" the engine, leave that trick for babies. You should check your coolant levl when it is cold and it should only be down about 1-2" in the radiator or 2/3rds the way full if you have the Harrison remote tank. Your motor could be running hot because of wrong ignition timing (retarded timing will cause a motor to run hot), lean carb jetting, bad water pump, clogged radiator, missing radiator seals (look at the Dr Rebuild site), and air pockets/leaks in the cooling system. I would check my ignition timing first, even though your emission sticker probably says 4 degrees before TDC, I would have it at least 8 if not 10-12 degrees before TDC. Are you running a "stock" set-up or is the engine rebuilt with a bigger cam, headers and other changes? Post your specs and does it get hot after start-up, driving down the road, idling at stop lights? More information will help.

Jul 17, 2005 | 12:23 PM

Fevre

Race Director

Joined: Mar 2001

Posts: 11,322

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From: Living in the Hartland

'Burping' the system generally refers to letting the eng go through a couple heat cycles to 'burp' the air out. Just make sure your reserve is full, drive it till it gets hot and you shoud hear it purging air, let it cool down, re-check you reserve level and fill as needed.

BTW a fresh or rebuilt eng will run hotter until broken it but follow the suggested items to check from the first poster.

Jul 17, 2005 | 04:39 PM

lars

Tech Contributor

Joined: Aug 1999

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From: At my Bar drinking and wrenching in Lafayette Colorado

American-built V8 engines don't need to be "burped." That's for Mercedes and some *** engines that are so poorly designed that they encapsulate air pockets during coolant filling. On Chevy V8, you fill the radiator, run the engine until the thermostat opens and begins to circulate, and then top it off. Nothing more to do. If it's full, it's full.

Jul 17, 2005 | 06:23 PM

marshrat99

Melting Slicks

Joined: Aug 2003

Posts: 2,135

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From: Dayton Oh

Here's what I do. With the engine cold, I take off the rad cap and run the engine while observing the coolent flow thru the top of the rad. When the engine starts getting hot enough to open the themostadt, it will start burping air. I keep adding coolent until it will not take any more. As you're adding coolant and the engine is getting warmer, you'll reach a point where the rad will take no more coolant and the coolant will actually start coming back out of the rad. Replace the rad cap at this point. Now you're done.

Jul 17, 2005 | 08:03 PM

WayneLBurnham

Racer

Joined: Dec 2001

Posts: 328

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From: Dallas County Texas

Man...mine needed burping a lot! I put on a manifold

filler neck and went with a restrictor plate instead of a thermostat to make it a quick, one time deal. I also have two manual cutoffs and no heater valver for the heater core - which could be as much a source of this phenomena as the tilted, lower mounted radiator, I really don't know.

I've never had this before on any other car or engine - including plenty of other GM's and a couple of SBC's.

I have had a number of other heating problems not related to this, including several blown headgaskets on this evil engine - but this is a different and real thing seperate from those problems once corrected doesn't pop back up until the next time I dump the radiator.

Before my manifold filler neck, after emptying the radiator and refilling, I would have to let it warm up and cool down a couple of times before all the air would finally move to the radiator when I parked on a big incline, then it was easy enough.

I did notice a a rapid heating when this would happen, and it wasn't every time I would empty the radiator but a number of times.

Jul 17, 2005 | 08:18 PM

Bullyj

Burning Brakes

Joined: Oct 2002

Posts: 971

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From: Rockwood TN

I agree with Lars

Fill the radiator start it and bring it up to temp with the cap off filling it as it needs it. When it's full put the cap back on and fill the overflow to the hot level you shouldn't have to do anythig else.

Jul 17, 2005 | 08:19 PM

C3nMe

Pro

Joined: Apr 2005

Posts: 603

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From: Illinois, USA

Quote:

Originally Posted by kessler

I have actually had to do this to another vehicle of mine (non-vette) and it involved running the engine with the radiator cap off at a slightly low level of coolant with the vehicle parked on an incline (engine up). This forces the air trapped towards the back of the engine to cycle to radiator and "burp" out. Since I did this right away, I did not run it long enough to determine if it would run hot.

An engine can run hot for a lot of reasons, several mentioned here. I also know an engine will run hot of the rate of coolant circulation is either too fast or too slow. The blend of anti-freeze to water being off can affect the heat transfer. A product like "Water Wetter" is supposed to drop temps up to 30 degrees, but I have no experience with these additives. A bad fan clutch can also be a problem (or if you put a undersized pulley on the water pump).

My experience with timing is that advancing the timing makes the cyclinder run hotter, as the hot gasses stay in the cylinder longer, and there is still compression going on.

It's just my .02c, but I hope it helps.

Brian.