I am experiencing a severe overheating problem and have tried just about everything. 1994 LT1 134,000 miles.
- Water pump, radiator, thermostat, hoses, rad cap all new.
- Temperature rises from ambient to 260 within 6 minutes, oil/tranny temp hardly have time to rise above 150, coolant temp gauge works also.
- Fans are on manual control switch and both work/turning on heater makes no diff.
- System has been bled and is free of air pockets
- Coolant flow through engine block is good.
- No visible leaks
- With one spark plug wire disconnected the temp stabilizes at about 230 and finally stops increasing. Also the #2 plug looks black compared with the others which are light gray.
I hooked up one of those prestone back flush tees to the heater hose and ran fresh hose water into the system. At the same time I have a 4' section of hose diverting water out of the radiator fill neck to the ground. With this "life support" hooked up the car maintains about 170 degrees and runs great (revs smooth, sounds healthy). However after unhooking the garden hose and putting the cap back on it overheated about 2-3 minutes later.
I'm still stumped. I posted this info in a reply to baddboy1705’s post Running HOTTT!!! HELP!! But realized I have tried all the suggestions in that thread. Anyone else have any idea why the engine would stay cool with fresh water but a brand new cooling system can’t keep temperature under control. BTW the first time it overheated was on the freeway about 65, temp went from 210 to 260+ fast and all the coolant had overflowed out of the radiator. Could it be something is causing the engine to generate more heat than the cooling system is capable of handling? Thanks for any input.

 

You may have blown head gasket on #2. That could be why it is not firing. That also explains why it overheats with your system capped off. Check for combustion gas in your coolant.

 

I'm sure you've thought about a head gasket being bad, but thats about what mine was doing when it was blown. When you take off the radiator cap while it's running, does the coolant seem like it has a lot of air in it, and the level of fluid varies constantly? You said it was free of air pockets, but mine was too except only for a short amount of time.

 

WHen you bleed it are you letting the engine run? IF not quit, refill the system with the bleeders open.. then take the cap off and run the car up to temp.

How old is the radiator? I had a GM radiator get stopped up after 1 year. It drove me crazy trying to find my overheating problem.

 

I've though about the head gasket and got a block tester but the results were inconclusive. Even with the radiator drained 1/2 way the coolant level rises to the tester by the time it gets to 200 - 210 and the fluid does not change color. Any tips on using the block tester, the instructions are not very helpful but it seems rather simple. What is really wierd is that the test fluid took over 5 minutes to change color when held in the exaust stream of the truck I'm driving right now.

 

Use a leak down tester. No confusion there. You'll know instantly where the problem is.

Along with a coolant pressure tester, you'll have all your bases covered.

 

EXACT same problem with my car...waterpump drive shaft stripped out and waterpump as new but wasnt moving.,..take the cap off when cold and take the thermostat out and start the car look in the readitor cap for moving water...hopefully thats not it but then again hopefully it is...u can get her back on the road with a new timing set....
hope that helps
Daniel

 

Daniel6718
I thought about this possibility but said to myself nah that can't happen till I read your post. I was thinking about a test to find out for sure. If I take off the water pump cover and disable the PCM/Fuel so the car won't start I can crank the engine over and look for the pump to move. When this happened to your car was there a noise associated with it? I've been hearing a sound like a pump failing that is louder when the car is hot but almost non-existent when cold. If the pump drive checks out I'm back to the head gasket and since I don't have a leak down tester time to get her towed to a shop.

 

You can check for head gasket using the coolant system pressure tester. Got to autozone and borrow it(about $70 deposit you get back when returned). You can pump it up to press and then start the car. If it starts jumping up into the red, its a head gasket. Its a lot easier than a compression tester but you would have to use that to find out which cylinder.

 

I was about to start a new thread, but his one fits close enough. Anywho, I have a 89 RS and swapped out the 305 FI with a new 355 (carb). She runs hot and I can't figure out why. There's plenty of flow, doesn't seem to leak anywhere and the regular fan was replaced with an electric fan, which is wired to be on full time right now while I figure out the problem. I've also replaced the thermostat to no avail... Any ideas ??

Mescaline

 

Well I took the front cover off the water pump and was able to rotate the water pump impeller with my hand!! Also with the engine running the impeller does not turn at all. Looks like Daniel6718 was right about the drive shaft for the pump being stripped. Now I just need to tear apart the front of the car to replace it. Well it's only 100+ outside right now, should be a piece of cake... Where is the best place to get the timing set & water pump drive shaft? too bad I can't just order the LT4 kit as I have a '94.

 

I thought I had the same problem with a 93 I just bought, turned out it "was" the problems as it had a brand new water pump, water pump drive, and coupler installed. The problem was two blown head gaskets due to overheating when it had it's previous cooling issue. Hopefully everything will be great when I get it back together.

 

I have the little water pump drive shaft parts. I just converted to electric. Let me know if you want em

 

I had the same problem, only when the car was moving I would overheat, stop and the temp would come back down. It was the front spoiler my wife parked by brail too many times, broke it off. Put a new one on and presto no more heating problems.

 

joshp007
Thanks, I'll let you know once I get it all apart, I will probably need a new timing set like Daniel6718 said so I'll probably get the drive gear with that. Thanks for offering.