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Discussion Starter · #1 ·
Here's the situation. I have a '95 Roadmaster Wagon with an LT-1 engine in it. Recently, I replaced the water pump and that project went smoothly. I also replaced the thermostat, radiator hoses, and heat sensor. But--- post installation, the engine got hot. I'd start it up, allow it to come to temperature, and would get a red "hot temp" indicator on the dash. The car runs smoothly. Now, I'm no pro mechanic, but I deo know enough to troubleshoot the basic issues. Here's what I've done so far.
> There are absolutely no leaks anywhere at the front of the engine. I spotted an extremely small drip at the top of the radiator and installed Stop Leak, which fixed that.​
> I bench-tested the new thermostat and it opens nicely. I even ran the engine with no thermostat and it still gets hot.​
> I have "burped" the cooling system multiple times and have the front raised. I had the heater on to keep trapped air from that system from intruding into the main cooling channels.​
> There is no water in the oil nor water coming out of the exhaust (blown head gasket).​
So, with the coolant topped off and everything buttoned up, I start the engine and let it come to temp, which is about ten minutes. The electric fan comes on, and everything seems fine, but then I get the "hot" light and the gauge continues to rise. For the life of me, I can't figure out what's going on.

Someone give me another thing to check.
 

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History or reason why you changed so many parts would be helpful.

Did you use an OEM ACDelco temperature sending unit (switch)? If not, you may have installed a defective unit - which may why you’re getting the warning.

When you get the hot warning, does the engine seem as though it is overheating? Is coolant being forced into the coolant reservoir?

If you increase the engine RPM’s while the car is parked, with the engine running (transmission in park) - does the gauge temperature drop or the hot light turn off?
 

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Discussion Starter · #3 ·
The water pump had a small leak and was making a noise, so that decision was easy. Thermostats are cheap and the hoses showed signs of age, so I changed those at the same time. After the hot indicators appeared the first ten times I started it, I decided the temperature indicator (from NAPA) might be the problem so that was the last thing I changed just today.

No, it really doesn't SEEM particularly hot, but the system is telling me it is so I'm taking the safe route. Yes, the coolant tank is completely full at that point.
 

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I suspect you have a defective coolant temperature sending unit. Did you add any sealer or teflon tape to the threads? Many GM vehicles ground the switch where it screws in the coolant jacket, and it does not require sealant (which could prevent a good ground).

Does the temperature gauge drop (when indicating hot), when you rev the engine to about 2,000 - 2,500 RPM’s?

If I recall correctly, the LT-1 engine that you have, has a reverse-flow cooling system. May sound rude (I’m not) - but are you sure you have all the air out?
 

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Discussion Starter · #5 ·
Does the temperature gauge drop (when indicating hot), when you rev the engine to about 2,000 - 2,500 RPM’s?

If I recall correctly, the LT-1 engine that you have, has a reverse-flow cooling system. May sound rude (I’m not) - but are you sure you have all the air out?
You and I think alike. I'm thinking it's an air pocket but multiple tries haven't gotten results. I read just now that GM designed it to take the air pockets out with the engine cold. Gonna try that.
 

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Discussion Starter · #6 ·
I'm still having the same problems. No visible leaks, no blown head gasket, and still the darn engine gets hot. Gonna flush the radiator today and try again.
 

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I suspect you have a defective coolant temperature sending unit. Did you add any sealer or teflon tape to the threads? Many GM vehicles ground the switch where it screws in the coolant jacket, and it does not require sealant (which could prevent a good ground).

Does the temperature gauge drop (when indicating hot), when you rev the engine to about 2,000 - 2,500 RPM’s?

If I recall correctly, the LT-1 engine that you have, has a reverse-flow cooling system. May sound rude (I’m not) - but are you sure you have all the air out?
 

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There is a air bleed that you must remove to allow trapped air to vent. Just cycling the engine won't get it. IIRC, it looks like a small pipe plug. Had to do it when i changed the water pump on my '96 RMW.
Jim
 

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Discussion Starter · #9 ·
Yes, there's a bleeder valve on the thermostat housing and also a capped outlet at the top of the radiator tank. I've "bled" the air out through both of those countless times but somehow air is still being introduced to the cooling system. The coolant overflow tank is old and suspect, so I've ordered a new one, but that wouldn't explain how air is entering the lines. After this, I'll have the radiator iteself tested.

Andy ideas?
There is a air bleed that you must remove to allow trapped air to vent. Just cycling the engine won't get it. IIRC, it looks like a small pipe plug. Had to do it when i changed the water pump on my '96 RMW.
Jim
 

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Discussion Starter · #12 ·
So, there's undoubtedly a leak between a cylinder and the cooling system, right? Cracked head? Blown head gasket? How do I figure it out?
 

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So, there's undoubtedly a leak between a cylinder and the cooling system, right? Cracked head? Blown head gasket? How do I figure it out?



I bought ordered and bought a new 1997 Chevrolet Camaro Z-28 30th-Anniversary convertible - with the LT-1 engine.

It was later repurchased by GM under my state’s lemon law after 14 separate defects were repaired by the dealer during the car’s first 4,000 miles. I presented the case using the BBB AutoLine arbitration process (then required in my state).

One of the defects were oil and engine coolant leaking from the rear of the engine, due to a defective intake manifold gasket. The problem was diagnosed and repaired by the dealer - but, I could smell the coolant and oil burning when the vehicle was driven. The dealer said it was leaking at the back of the engine.

I did not do the repair work - but I would suspect you would have to do a pressure leak down test, and also remove one or both of the cylinder heads for inspection.
 

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Sure sounds like a bad head gasket to me. You don't always see water in the oil or white smoke coming out the tail pipe. Does the coolant bubble at all in the radiator? You can get an engine block tester to check for combustion gases present in the coolant. I would do that next.
 
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