Topic: GM 3.8 running hot

I've got a BOP 3.8, probably from an 80's G-body. Recently rebuilt and runs great, but seems to run hot. My old 70's 231 ran at 180 all the time, and this one dropped into the same car will easily go over 210 if we push it too hard. We had to back off at CMP to keep it under 210. We sealed up all gaps around the radiator and built a shroud in front of it to make sure all air that comes in the front goes through it, and that let us go faster before it got too hot, but I can still run it up past 210 if I push too hard. Managing our pace (keep laps over 2:20 at CMP), it will easily go all weekend without issues, and it uses no water or oil or otherwise acts broken, although the exhaust does pop loudly under deceleration, which our old engine didn't do.

Details:
big new aluminum radiator with fans
oil cooler
cleaned and flushed coolant system
timing set to 17 BTDC at 600 RPM with vacuum line removed from distributor.
distilled water with one bottle of Water Wetter
thermostat removed

Everybody grab your brooms, it's shenanigans!

Re: GM 3.8 running hot

I know in the past we would overheat on SBC with a removed thermostat. The trick was to remove the moving baffle in the thermostat but put the body of it back in for a bit of backpressure. We wouldn't get god flow through the heads otherwise.

Re: GM 3.8 running hot

did you remove the thermostat on the old one too? or is that a change? Some engines do not react kindly to completely removing the thermostat.

Any AFR gauge to see if this engine is running more lean than the old one?

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Re: GM 3.8 running hot

Engine bay pics could help spot issues.

Run with a thermostat or at least a restrictor.  Will keep radiator pressures down and prevent it from exploding.

Is there a spring in the lower radiator hose?  It may be collapsing when it gets hot, restricting flow.

Why are you running with vacuum advance disconnected?  What is total timing at ~3000rpm with the vacuum disconnected?  17 initial may put you too high under load.  May not help with cooling, though.

Re: GM 3.8 running hot

I will try the thermostat, that's a cheap/easy fix and the old engine did have a thermostat. I've removed them on so many Hondas; I think of them as a failure point on a race car.

Disconnecting the vacuum hose was just to set the timing, we run the car with it connected.

The lower hose should have a spring in it, but I can easily mash it by hand, so maybe that rusted away. I'll replace that as well.

Engine bay:
http://www.carolinahondas.com/members/roger-albums-pj-picture6830-stagbay1.jpg

http://www.carolinahondas.com/members/roger-albums-pj-picture6831-stagbay2.jpg

Everybody grab your brooms, it's shenanigans!

Re: GM 3.8 running hot

look into "running lean" or vacuum leak, intake manifold gaskets

cover over hole in hood, hood scoops can pressurize the engine compartment stopping airflow through the radiator

'ported, relieved, with bored-out arm rests, and oversize seat covers.

Re: GM 3.8 running hot

Wow, put a thermostat in it and a new lower hose on it and it goes straight to the thermostat temp and doesn't budge. I even put a 160-degree thermostat in it. It was sitting there idling at 200-210 before. The old hose didn't actually look that bad, and it ran at thermostat temp (180) on the old engine, so I'm guessing these engines must need a thermostat to work correctly.

Thanks for all the guidance, I think this one's fixed.

Everybody grab your brooms, it's shenanigans!

Re: GM 3.8 running hot

Awesome. Glad to hear its working better.