LT1 tries to overheat very quickly.. about 240deg in less than a minute and it will keep going until it settles at 250-60 which is redline, but I've seen the needle go farther once and would prefer it never to do that again. So far I've replaced the thermostat (160deg installed to replace the stock 190deg), the water pump, and the coolant temp sensor on the water pump. There is pressure in the return line from the thermostat while hot, and definitely can feel fluid motion in the pipe.

I have not replaced the coolant temp sender that only talks to the PCM, but I’m curious as to whether a clogged fuel filter would cause the engine to run very lean and thus hot? Its only got water for coolant right now, but that shouldn't let it heat up so quickly, and I don't want to put in the $30 of GM Dexcool until I know the cooling system is solid.

I'm going to try reverse flushing the engine next to see if there is some type of blockage in the bottom end, but with the water I’m pulling from the radiator, and the water that purged from the water pump re-installation was all clean. Still haven't pulled the knock-sensor to properly drain the block because I need a 7/8" socket as there is no way to get a wrench in there, but look to do this next if reverse flush comes up clean.

Any thoughts or suggestions would be immensely appreciated.

Check my signature for engine details if you need them.

 

Get the proper 50/50 mix of coolant and water in there. You don't want to run straight water.

Also, have you bled the system properly?

 

sounds like a problem i had with mine is it useing any collant at all ? and have u bleed the system to? mine end up being the head gaskests never smoked or any thing but was eating collant and water and it was not even going in the oil was vapirizing by the time it got out the tail pipe

 

Have you bothered to replace the coolant temp sensor in the head? that one controls the gauge.

 

if it really got that hot, 260+ degrees chances are you did some damage to head gasket or cracked the head. Nice job. next time shut it off before it gets that hot

 

Try to bleed the system properly first, before starting.

 

Did you forget the coupler for the WP?

At those temps you probably softened the heads.

These systems do need bleeding after filling.

Straight water actually cools BETTER than 50/50mix. It just lacks lubricant for the pump and anti corrosive additives. So basically straight water will not cause overheating.


Far as $30 worth of Dexcool. Just go to the parts store or Walmart and get the yellow "mix with anything".

 

I did bleed the system, and I did install the coupling, ensuring there was no play on either the spline from the engine or the spline on the water pump.

Engine gasket failure was mentioned by someone offline, but dismissed a bit because there is no evidence of coolant leaking into the oil. Also, when there was coolant 50/50 mixed in the cooling system, I couldn't smell any burned coolant in my exhaust, but thats a somewhat subjective test of gasket failure.

And you're right about the 100% water, 96capricemgr. The only point of anti-freeze is to make the freezing point of water lower and the boiling point higher. If pure water was so bad for cooling systems cooling, you'd see overheated engines constantly at the strip because of the strict no coolant rules for track safety.

I'll update again once I get the system re-flushed and swap the cylinder head sensor. Would have done it today, but I don't have a garage, and I have t-storms overhead while trying to do all the work on the curb.