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Discussion Starter #1
I'm a new member with an issue and looking for guidance please.

I have a 2000 Honda Odyssey with 200K+ on the odometer. It is overheating on the road. When started for cold it will slowly read hot on the temp gauge, then pass normal operating temp and push to hot.

I have changed the themostat, thinking that was the issue. That has not fixed the issue. The top coolant hose is hot, the lower hose that goes to the thermostat is not. No heat in the van through the vents. When the lower hose is pumped agressively by hand I can make the temp gauge return to close to normal.

It is possible that there is a small head gasket leak, but not enough to see coolant pouring out and no milky residue in the oil either. The head gasket was confirmed by a dye test.

I was leaning towards the water pump being the issue, but wanted some experieced opinions before getting into a job of that size. I also read something about the temp sensor or a temp valve near the thermostat being a possible issue. Any thoughts or suggestions on how to further troubleshoot or repair are very appreciated.
 

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Few things to rule out before thinking about water pump or head gasket:-

1) Air pocket in the cooling system
2) Blockage in the cooling system
3) Hoses collapsing under suction
4) Bad thermostat (your new one could still be bad)

- Since your engine is getting hot but you are not getting any heat, most likely you have an air in the system. You need to bleed it or use the special funnel (spill-proof?) to fill the system. If you can get to the hoses, replace them anyway. Verify that thermostat is opening by putting in a pot of boiling water and checking that it opens up. I have a 150K waterpump in my basement and that looks as good as new. It is highly unlikely that your waterpump has lost its fins unless there was wrong coolant in the system. My coolant was changed at 10yrs/150K miles.
 

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We did have a guy with a similar issue...and he found that the water pump impeller was starting to "free wheel". In short, it was not pumping like it should have. This was a brand new water pump, too!

OF
 

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Did you check the coolant level in the reservoir? If it's okay there, check the level in the radiator when the engine is COLD. It should be right up to the neck. A faulty radiator cap might cause the coolant to purge from the engine when hot but not pull it back when cold.
 

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Discussion Starter #6
This is our second thermostat installed, both brand new and both had a very easy push. I will verify that the one we removed was functional with the hot water test.

The system was functioning fine until the initial overheat. The cap seems to be holding pressure, no collapsed hoses are visable. There did not appear to be any coolant draw or return from the overflow while it was running, but the overflow is properly filled when cool.

I will effort the spill proof funnel. It just seems as if there is no flow or pressure to the system that would allow it to cycle. If the head gasket leak were that bad I would expect a puddle of coolant to be leaking from the lack of pressure, but its just a small amount of steam under revving load.

Is there any way to confirm the pump is functioning properly without removing it?

Thanks guys. This is our delivery vehicle at work and I already had to go buy a replacement, but I much prefer this vehicle.
 

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Is this the original water pump at 200K miles? If so, it very well could be a faulty water pump causing the overheating. Not sure on testing the pump except for removing the pump for inspection or checking the flow through the engine and radiator. The next timing belt service is at 210 K miles so you are very close to it and generally it is cost effective to replace the water pump at the same time.
 

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Discussion Starter #8
I confirmed that the thermostat we removed from the vehicle was functional, so its not the thermostat 100%.

Its looking more and more likely that the water pump is the culprit here. I will see what is needed to replace the pump and timing belt(s). I will remove the rear timing cover first to see if the pump is showing any overt signs of failure.
 

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Couldn't you take one of hose off and just crank the engine to see if the water starts pouring out? I am not sure if that is the correct test. Otherwise, you could try it at idle for couple of seconds.
 
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