Overheating Issues with 96 STS

[Jamdub]

I have a 1996 STS. 173K miles. The engine is solid, and over the last year I started having overheating issues. My mechanic said I had air in my system. So he bled the cooling system. He was working hard on bleeding the system. Too hard I felt. These cars are supposed to be self bleeding. So I was suspicious. We replaced the thermostat, twice. Car still ran hotter than it should. In stop and go traffic it would run up to 250--with the blower on full blast!! And going up hill it would actually hit red if I didn't turn the blower on. Long story short, after replacing the thermostat, checking the purge line repeatedly, replacing the water pump, my car still ran hotter than it should. One day I read about the heater core busting and coolant showing on the floor of another car. So I asked my mechanic to check out my heater core. We saw a little drip underneath the car, but there was nothing on my floor board. I told him to replace it anyway. Once that was replaced, the cooling system is running tip top! And when he go inside the dashboard and saw the core, he told me it was leaking. Now, my car never goes past the 195-220 mark in normal conditions. In traffic, without the blower on, it doesn't go past the 235 mark, and usually doesn't quote hit the 235 mark. In severe traffic, stop and go, and sitting, it doesn't go past 240ish - no blower on.

I am writing this, because I expected to see coolant on the passenger side floor with a bad heater core. The fact is, your core could be compromised and not show signs, and that could be the cause of your overheating. Anyone with overheating issues, solid engine and cant solve their problems, take a look at your core.

Adios

[Cadillac Jim]

Thanks for sharing. This is a valuable tip.

[BodybyFisher]

This is good info. There is a hose at the bottom of the hvac unit that exhausts to the street, you were losing coolant and it was going into the street. Oddly however, you should have smelled coolant coming through the vents or from the heater. Its a very distinct sweet smell, I am shocked you didn't smell it over the last year. Even more surprising is that a leak in the heater core will cause condensation on the inside of the windshield under certain conditions.. very odd indeed

[rockfangd]

Excellent. Thanks for posting this. Also heatercore is not bad at all to do on this setup

[joeb]

Well, OP said car was running hot. 250f is hot. BUT, turning on heat to tweak engine operating temp is sketchy at best. I understand the concept but no heater core is going to regulate an overheating motor. He never mentioned h was losing a LOT of coolant. Or he was 1 gal low or so on. He replaced core and all is good? Not buying his theory of bad core, hot motor.

[Cadillac Jim]

If the bypass is clogged, turning on the heater will take up some or all of its function. Other than needing the heater on for the cooling system to function normally, everything seemed OK. This was a symptom of a recently-worked-on 1959 Chevrolet six once that led us to pull the head and find a shop rag stuffed into the cooling passages that blocked the bypass.

The cooling system on this car was overdone, hence the nickname of the 235 cid Chevrolet sixes, "cold-water six." Once I used second gear to lay off the brakes while descending from a mountain pass and the temperature gauge eventually pegged to cold, just like it had been parked overnight on a cool evening, just on the water that passed a closed thermostat through the bypass.

[BodybyFisher]

Well, OP said car was running hot. 250f is hot. BUT, turning on heat to tweak engine operating temp is sketchy at best. I understand the concept but no heater core is going to regulate an overheating motor. He never mentioned h was losing a LOT of coolant. Or he was 1 gal low or so on. He replaced core and all is good? Not buying his theory of bad core, hot motor.

I hear ya, that is what I was getting at above.... Something tells me that its possible that a clog in the bolt with a hole in it might have been cleared allowing air out and the heater core was just something else wrong...

[adallak]

I do not think heater core plays significant role in cooling the engine. Leaky core could depressurize the system and ,make it boil over, which did not happen. Very strange.

[Cadillac Jim]

The heater core isn't supposed to have much effect on the cooling system. If it does, the bypass is probably clogged.

[Jamdub]

I never saw condensation on windshield, but I did smell coolant from time to time; I also did run low on coolant - often. I have another car, so I didn't have my nose, eyes and ears tuned to the car as if it was my only vehicle. Also, the purge line could have been plugged as well. My mechanic said he needed to purge the air out, which I found strange. When he purged the system, that may have cleared a clog. That's the problem with working on several issues, you never know where the problem actually occurred. But after purging, new thermostat and water pump, the car still ran hot in traffic. Once the heater core was changed, I haven't had any issues.

[Cadillac Jim]

If you smell coolant inside the car, your heater core is probably leaking. Note that if you have coolant leaking under the hood, you may be able to smell it through the cowl vent. The way to tell for sure is to get down and check the carpet near the center of the car in the footwell on the passenger side. If it's damp, or if you can smell coolant, the heater core is very likely leaking.