oil cooler problem contributing to higher running temperature?

[landlocked]

Lately, my 94 Camry occasionally runs a few degrees hotter after leaving the highway and driving home on country roads (speed reduced from 60 to 25 mph). We just noticed a 'slight' fluid (not sure if oil or coolant) leak coming from under the oil cooler and wondered if that would cause our problem? No noticeable drop in coolant or oil level. Outside air temp is cool.

History:
Mar 2005 - premature water pump failure on highway - engine overheated- towed car to shop and had 180k mile service (including new water pump)
Nov 2005 - after 10k miles without problems - overheating began
Dec 2005 - we (wife and I) replaced thermostat, fan sensor, radiator cap with OEM parts - replaced radiator with after market - tested new parts
Mar 2006 - mechanic replaced leaking head gasket and two radiator hoses - overheating seemed to be 99% resolved

Our mechanic (a good one) thinks our problem is more likely related to malfunctioning thermostat even though we used OEM parts and installed in accordance with manual. Fans automatically come when temp is high enough.

Has anyone had this kind of problem? Any suggestions?

[Toysrme]

It's possible, but extremely unlikely.
As in, I've never heard of the oil cooler cracking on any modern Toyota engine. *Any*.

If you see a stain directly under it, it's probably spilled oil from changing the filter. Toyota oil coolers are nearly universally located directly behind the oil-filter mount.

Mar 2006 - mechanic replaced leaking head gasket and two radiator hoses - overheating seemed to be 99% resolved

Ya warped the head<s> when overheating.

I tend to agree with the mechanic. While Toyota thermostats are way better than most it is fairly common for them to be defective when bought. It's also very common for them to be installed incorrectly.


Replace the thermostat again & if you continue to have an overheating problem. Check that the coolant temp sensor isn't lieing & check the radiator. It came with Toyota red coolant & if you ditched that for a normal coolant without flushing it well... That will cause a hard gel to form. Clogging the cooling system.

[landlocked]

Thanks for the advice.

You were correct about the oil cooler not failing although a very small amount of oil was leaking past either the seal or gasket between the oil cooler and the engine. I only had to buy a larger metric socket to do the repair by replacing a seal and a gasket.

I was chasing a phantom heating problem since it turned out to be a faulty engine coolant sendor that was sending bogus info to the gauge. My sendor failed the hot water / resistance test.

Both the Toyota parts guy and I learned that there is a big difference between a sensor and a sendor. When I showed him the failed part and we tried to order the sensor, we learned that sensors talk to the computer and sendors talk to gauges.