Engine temperature going up & down, bad thermosta?

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orlando,FL
2002 Honda Odyssey 421k

I installed the new thermostat (not OEM). Both fans are coming on at 235F then it will goes back to normal temperature which is 180F until the fans turn off. Is this normal? I did changed the coolant and bleed the air so many time. Yes, I did the combustion leak test and the results was negative.

Parts that been changed;
Thermostat
Thermostic switch A (on thermostat housing)
Thermostic switch B ( NEVER been changed, located somewhere on passenger side of the engine)
Upper & Lower Radiator hose
 
Is this new behavior or newly noticed? Is this per the dash gauge or a scan gauge?
 
It is indeed possible to have a "lazy" or "weak" thermostat. I've had a cheap aftermarket one fail like this in short order.
 
Originally Posted By: Trav
235 sounds high, did you get the system bled properly?


yes sir, with the cap off and let it run until I see it about to start boiling so right there I go ahead and put the cap back on there. Heater control all the way to full setting. I bled the system so many times. I was thinking about buying the new thermostat motorad 302-180.
 
Originally Posted By: eljefino
Is this new behavior or newly noticed? Is this per the dash gauge or a scan gauge?


It been doing this since we installed the thermostat but then I didn't drive the car for one year because I also had a cel on this car that I had to fix it. I already fix the cel now trying to fix the overheating problem. I'm looking at both. I have scan tool. When I see temperature guage on the car going up at 230F that's when the both fans is coming on after 5 seconds it will drop down to normal temperature 180F.
 
How about that water pump. Does temperature come back down when you rev it up? Could be failing.

Look for small puddles, they usually have weep holes...

*FWIW: I speak from experience. You can have changed everything and if the water pump is failing, either the impeller has disintegrated or its spinning on the belt but not at the impeller or whatever, its not going to cool as effectively and this is possibly indicative of a failing water pump, not just a possible stuck or sticky or cheap stat. You seem to have listed every part changed BUT the water pump.

Aside from radiator cap itself, check that out too.
 
When the fans come on are they throwing serious heat? I suspect your thermostat is a dud and not letting hot water to the radiator, so the fans will blow air over lukewarm if not cold water until the t-stat lets a glug of engine super-heated coolant out to the rad.

If a car is nearly overheating the driver should be able to stand by his door with the fan going nuts and feeling the heat coming from the firewall area.

No fan I've ever seen can suck 40 degrees out in 5 seconds. Takes a minute or two if the thermostat is wide open.
 
The first thing I'd do if the system is properly bled is put an OE thermostat in. Aftermarket thermostats in my experience are hit or miss at best. Hopefully that fixes your problem. 235 is high for the fans to kick in I wonder if they can be programmed to come on sooner?
 
Originally Posted By: Carbuff
Like Ethan, I've had new non-Honda t-stats do what yours is doing.

I've learned to stick with Honda thermostats on Hondas.


The reason I was thinking about installing motorad 302-180 is because on odyfamily forum had a great result on the motorad 302-180 thermostat. Gave them more heat in the cabin. Here's the link; http://www.odyclub.com/forums/24-1999-20...cs/31696?page=7
 
Originally Posted By: Prune_Juice
How about that water pump. Does temperature come back down when you rev it up? Could be failing.

Look for small puddles, they usually have weep holes...

*FWIW: I speak from experience. You can have changed everything and if the water pump is failing, either the impeller has disintegrated or its spinning on the belt but not at the impeller or whatever, its not going to cool as effectively and this is possibly indicative of a failing water pump, not just a possible stuck or sticky or cheap stat. You seem to have listed every part changed BUT the water pump.

Aside from radiator cap itself, check that out too.


This car belong to my father so I don't know when last time he changed the water pump but I do know that when he does it is when he's doing the timing belt job. I do not see any coolant on the ground or on the timing belt cover underneath. I don't hear any noise on the startup so I didn't bother about the water pump. I did put new radiator cap OEM sorry forgot to mention that here. Let me look into it more on the car again.
 
Okay I'm going to put the OEM thermostat in and see what will happen. If this doesn't solve my problem then water pump will go in. How will I know if I'm getting up to date on the thermostat and not older model like old stock?
 
Originally Posted By: WobblyElvis
Bad thermostat.
Cracked head letting air into the system.
Plugged heater core circuit.


How I can see if there is crack head? You mean crack headgasket?
I just flushed the heater core first time.
 
There is absolutely no effin way the temperature drops 50 degrees in 5 seconds when the fan(s) come on especially if the car is stationary. Physics does NOT allow that. I take it back. If the thermostat stays stuck until it reached 230 and then suddenly open up, I could see temperature dropping very fast because now the cold water and the very hot water will mix. You can verify this theory by feeling the hoses and see when they transition from being soft cold to hard hot. That tells you that the thermostat has now opened up. Looks like you should just get a new OEM thermostat from the dealer if you are going to do the job again.

Is dash board gauge mirroring the numbers you are seeing on the scanner?

On the related topic, I need to know the steps involved in replacing the thermostat. If you don't mind, can you take some picture during the procedure?

I am presuming you replaced the FPR regulator and that problem has been now taken care of?
 
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