Running Warmer than Normal - 2009 base, manual

[PalouseAveo]

I have a 2009 Aveo5, base model, no A/C. ~260,000 miles.

It is running warmer than usual, with the heat gauge just shy of the halfway mark; it normally sits just over the 1/4 mark. In addition the engine bay gives off a considerable amount of heat after driving. Here is a description of what led up to the problem and what I have done since....

A few weeks ago I was replacing the blower motor (GM 95978693) and cabin air filter because I wasn't getting any air movement from the vents. I noticed the lower radiator hose and one of the heater core hoses were starting to balloon, so I replaced them too. I also decided to flush the radiator (with distilled water) and add new coolant (DexCool). I followed the flushing procedures in the Haynes manual.

After replacing the hoses and flushing, I noticed a leak and found several cracks in the coolant expansion tank. At this point, I decided to replace the expansion tank along with the rest of the cooling system hoses.

After replacing the expansion tank and hoses and refilling the coolant, I noticed the radiator fan was not turning on after reaching operating temperature. This is the first time I noticed the temperature raising higher than normal.

I replaced the Fan Hi Relay (GM 6484304), the Fan Low Relay (GM 96590287), and the Radiator Fan Resistor (GM 94812213). The radiator fan still did not work, so I replaced the whole radiator fan assembly.

The radiator fan now works properly, but the temperature gauge still indicates the car is running hotter than normal.

I am wondering what could be causing this problem. Thermostat, water pump, something else? The water pump was replaced ~20,000 miles (6 months) ago.

Thanks

[slayerized6]

Temp gauge should normally be at the halfway mark. But you need to correctly diagnose your issue before you just throw parts at it. Did you test the coolant temp sensor to make sure it was still good? Did you use a scan tool to read the coolant temp from the OBD2 port?

[Deano]

I am not sure about the running warmer than normal issue. But by your description of the swollen hoses and the cracks in the expansion tank, those are classic signs that engine oil is mixing with your coolant via a failing engine oil cooler. The 2009-2011 Aveos have the engine oil cooler, and the internal seals harden and leak after 4-5 years. I am surprised that you managed to get so many miles on the car without yet having replaced the engine oil cooler.

Deano

[PalouseAveo]

Temp gauge should normally be at the halfway mark. But you need to correctly diagnose your issue before you just throw parts at it. Did you test the coolant temp sensor to make sure it was still good? Did you use a scan tool to read the coolant temp from the OBD2 port?

Thanks for the reply. No, I haven't tested the ECT sensor or used a scan tool to read the temp. I should be able to borrow an OBD2 scanner, but I'm not sure about testing the ECT sensor. Is that something best left for a mechanic? Could I do it with a multimeter, or would I need a specialized tool? The past few years I've been trying to as much maintenance myself as possible, but I admit there are some things a mechanic should do.

Regarding the temperature gauge. Mine has never gone to halfway in the 10+ years I've had it. It has always sat around or just below 3/8. Right now it sits exactly at halfway most of the time and goes slightly over sometimes.

[PalouseAveo]

I am not sure about the running warmer than normal issue. But by your description of the swollen hoses and the cracks in the expansion tank, those are classic signs that engine oil is mixing with your coolant via a failing engine oil cooler. The 2009-2011 Aveos have the engine oil cooler, and the internal seals harden and leak after 4-5 years. I am surprised that you managed to get so many miles on the car without yet having replaced the engine oil cooler.

Deano

Right on, thanks for input. I checked the Haynes manual and it seems like a relatively simple replacement. Would you recommend replacing the entire oil cooler unit (93186324) plus inlet/outlet seals? Or would it be OK to just dissemble the oil cooler and replace the internal seal (5199750)? Should the inlet and outlet lines also be replaced?

[Deano]

Good question. When I replaced my engine oil cooler, I had all new parts ready to go. New oil cooler, and 3 new coolant pipes. The new engine oil cooler comes with all the attaching seals. And the new pipes come with their all seals. Even though I might have been able to reuse the old cooler and dissemble it, and replace the internal seals, I didn't bother. Because i wanted to get the repair done as quick as possible with the least possibility of complications. If you have lots of time, it might be worth the bother to dissemble the old engine oil cooler and rebuild it with new internal seals. If you are careful, you can probably reuse the 3 coolant pipes if you install new seals on the old coolant pipes.

Deano

[PalouseAveo]

Thanks Deano!