For the past several months, my Odyssey has been getting really hot (not in the red, but very close to it) when I am going uphill. It can be 65 degrees or 100 degrees, it still does it. If I put the heater on, it cools a bit, but not until I start driving downhill.

I took it to a mechanic and he tested it. He took it over several local hills here and he said that it gets hot, but doesn't overheat. He checked for leaks, coolant levels, put it under pressure, and all was okay. He also took a lot of time to check for problems with the head gasket. Not sure where to go now. I don't have a ton of money, so I don't want to spend too much time doing things that won't help.

It has 95k miles on it. Thanks!! I need some direction...

 

At what temp does the thermostat open?
Original water pump still in the car?
Any build up in the radiator/overflow?
Have you tried a flush (not drain and fill)?
What did the mechanic say, and if nothing, did you still have to pay?

 

At what temp does the thermostat open?
Not sure. The mechanic said that it seems to be working right.

Original water pump still in the car?
Yes. I need to do a timing belt with water pump replacement soon.

Any build up in the radiator/overflow?
He said it looked clean and levels were good.

Have you tried a flush (not drain and fill)?
I was thinking that would be my next step.

What did the mechanic say, and if nothing, did you still have to pay?
He just said that he couldn't get it to overheat, just that it ran hot when there was a load (going over the hills). But it doesn't do it when the A/C is on and it is over 100 degrees. Only climbing. He charged me $50 for his time for all the testing. The mechanic is very well-known here, for his good reputation, though it was the first time I took my car in...

 

When going over long hills repeatedly it would be better for you to change gears to D3 instead of D4. This will help keep your motor a bit cooler. I experienced this with my CRV a while back. In case of emergency, take your windows down and blow your heat on HIGH to relieve some pressure and that will cool down the motor too.

 

I have never had this issue with my 96 Odyssey. I would suspect a bad thermostat or old coolant. Did your mechanic check to see if the thermostat is working correctly? With 95kmiles on your Odyssey, it wouldn't hurt to replace the thermostat when you are having your timing belt and water pump replaced. I replaced my timing belt, water pump, thermostat, all belts, and radiator hoses at 100K. Everything was working fine at the time of the preventive maintenance.

 

Also check your radiator fan, I've seen them go out and owners not realize it due to air outside air cooling motor.