My 94 Camry V6 started overcooling last week after I topped off the coolant. (Has a small leak from the top of the radiator.) The needle barely gets off the cold line even in city driving with 100+ heat.

I replaced the thermostat, but it is still running just as cool. I'm not sure what to check next. Maybe the temperature sensor itself? If so, where is that?

Any other ideas?

Thanks in advance for the help

 

I've got the same car, same engine. Just had radiator, water pump, hoses, thermostat replaced.

My mechanic stuck an oven thermometer in the fill block when the car restarted. He didn't say why. But I would guess he wanted a verification of what the instrument panel gauge was indicating.

With the engine running for a while, would it help if you put a rag over your hand and then touched the radiator top tank? And, after replacing the thermostat, did you burp the air out of the lines?

Adding coolant to a cold system through the fill cap results in an air pocket the size of Nebraska on the engine side of the thermostat. When the thermostat is in that air pocket, it doesn't open up because it isn't in contact with hot water, so it isn't activated. Crazy, huh? And I don't know which side of the thermostat contains the temp sensor.

 

I never would have thought of that. Thanks for the tip.

...if the thermostat isn't opening up, won't it be overheating because coolant isn't allowed to flow into the engine block?

Either way, how does one go about bleeding the coolant lines of air pockets?

 

Though if the temp gauge is on the engine side, that would explain why it's reading cool... Hmm.

 

I'm not a mechanic so I don't know the definitive answer about the sensor gauge.

But, here is how my guy got rid of the air pocket. The engine tended to overheat after the radiator/thermostat install.

So, he opened the hood with the engine running ( and hot as hell ) and open the thermostat cap with a big towel over it to protect his hands. Scary stuff, I thought.

He began to add Antifreeze. The engine would burp it back at him. He added more. He kept repeating this until the level was at the top of the filler block (the aluminum water manifold where the cap attaches). The level seem to stabilize.

The geysers were cause by steam pockets, not merely the hot coolant. Things settled down, and the temps have been stabile since April.

A final thought. If you can be sure your entire system is full of coolant, and free of air pockets, then and only then can you get a correct temp reading. If it's full and the panel gauge reads cold, you know you have a bad temp sensor.

 

fixed it for you. try to keep 50:50 mix of antifreeze and de-ionized water,
which is what pre-diluted is. same cost per gallon in auto parts store, looks like same jug.

 

Yup. Mechanic used 50/50 antifreeze, straight from the jug. I didn't know that stuff was de-ionized. Does that have the same effect as distilled water in preventing corrosion?

I know the Ferrari owners insist on distilled water for their engines. Snobs, just like my wife who want eat anything that isn't 'organic'. La-dee-da.

 

Thanks for the tip on burping the cooling system. I'll be sure to do that to make sure I'm getting an accurate reading. Though since my system is overcooling and not overheating, I'm not sure it's the root of the problem.

My hunch is it's a bad temp sensor. Time to throw some parts at the car and hope it works...

 

Yes, kinda, it has the same effect in preventing scale deposits.

 

So, the plot thickens.

Replaced the temp sensor today, and sure enough, it started reading true. The engine was definitely not overcooling. It was overheating for the last week and a half.

Driving around a bit, I noticed two things. First, it got up to about the 2/3 to 3/4 mark during the drive (bad), but did not reach above that (good). Second, it ran cooler at idle (about the half mark) than during acceleration and highway cruising, telling me that the coolant system is not circulating the coolant properly.

I have not heard any squeaky or grinding noises while driving, implying hopefully that the water pump is operating properly. The radiator has been leaking slowly from the top since I bought it a year ago, so I'm inclined to think it's a bad/clogged radiator. O'Reilly has one listed online for $114.

Any insights? Is there a definitive test I can do or get done to determine if it is in fact the radiator before I buy a new part?