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Update :I'm thinking tstat, what do you guys think?

Still trying to figure out if my 2000 Honda Passport with 3.2 has a bad tstat or water pump, but in am strongly leaning to thermostat… This is why.

Now that I understand the cooling system on this truck better (it’s like no other I have ever seen with the tstat on the water intake side on not the pump out)… I am getting heat which tells me water is pumping. The top rad hose is getting hot (again points to water pump pushing water), radiator stays cold, as does lower radiator hose, and lower tank (fins run up and down on my rad)… Sure sounds like a closed stat…

And with the heater on the temp comes down slightly.

If it was an easy job I would just do it to be done with it, but it’s such a PITA on this truck (the intake must come off) I really don’t want to do it if its working…

Am I missing anything ?? What are your guys thoughts???

Have you checked yet to see if the radiator flows at all? You could accomplish this by simply running a garden hose into it and seeing if it drains from the lower hose port.

I drained fluid from it the other day, when I tested it for a bad head gasket with the blue fluid puffer thing… It seemed to drain from the tank just fine…

I will double check before getting to far into the job, after I drain the rad and pull the hoses. I also need to check for any plugs that may have been in the radiator when installed as someone else pointed out to me.

The thermostat is on the intake side of my Honda Accord and on my Saturn, seems to be the new way. They are on the end of the lower radiator hose.

13+ years on a thermostat? Long enough IMHO. Just change it.

Back when I changed green coolant every 2 years I’d change the thermostat & rad cap every 4 years.
Now with long life coolant I’d do coolant, thermostat & cap every 5 years on a daily driver.
Since I only drive 2-3 times a week I’m stretching the thermostat & cap to 10 years.

My gambling money is still on the thermostat.

Just my 2 cents, but I consider the T-stat a maintenance item to be changed every so many years even if it has not failed. I do realize that some of them are a pain in the neck to do.


Is the car overheating? If the ambient temperature is extremely low the water flowing through the heater may be enough to cool the engine. And if the thermostat opens only minimally the upper hose might get hot but the water gets cold as it travels slowly down the flues. What is your weather like there?

Rod, yes over heating… Takes about 5 miles air temp is in the 70’s. At idle with the heat one it does not overheat. I’m going to replace the tstat, as it’s the cheapest thing and seems most likely.

Before you drain the coolant, get the thing so it’s nice and hot, shut it off and immediately carefully feel all around the radiator for any cold spots. It should be uniformly warm and gradually cool off towards the bottom. Any sharp differences in temperature anywhere indicate a plugged radiator.

@ok4450: “Just my 2 cents, but I consider the T-stat a maintenance item to be changed every so many years even if it has not failed. I do realize that some of them are a pain in the neck to do.”

Like the V6 Audis and VWs that require removal of the timing belt to access the t-stat?

It sure sounds like a stuck-closed (maybe only partially) t-stat to me from the symptoms. The t-stat on my Corolla is sort of a double action gadget, when it activates, it opens one fluid flow path, and closes another. So I can imagine the symptoms if it didn’t work quite right could be somewhat confusing. I’m able to look inside the radiator and see when the t-stat opens, b/c I’ll see water pouring in. Are you able to see that happen? You could remove the top hose from the radiator and see if any or how much water comes out from the engine – as it heats up – maybe as a guide to how much the t-stat is opening. When mine opens, the water really pours out big time from that hose, like turning the bathtub faucet full on.

The thermostat is cheap enough that if I’d just change it first to see what happens before driving yourself crazy looking for other possibilities.

I agree that the thermostat is the likely cause of the problem and as described it sounds like a by-pass thermostat that channels coolant to flow internally when cold and as the coolant heats coolant is diverted to the radiator. When at the rated temperature the thermostat likely must totally plug off the recirculate port to force all flow to the radiator, I recall some peculiar problems with Ford V-6s that used such a system Very aggravating.

@asemaster: “Like the V6 Audis and VWs that require removal of the timing belt to access the t-stat?”

Sounds like changing the t-stat should be on the list of extras at each scheduled belt change.

I’m a little curious as to why you have to remove the upper intake manifold. Isn’t the thermostat in the goose neck of the lower radiator hose, not the upper one?

@keith, unfortunately the thermostat is buried under the intake manifold in this engine. Here’s a guy taking off the manifold to replace the tstat on a '98 Passport:


I highly recommend installing a genuine Honda thermostat. I’ve noticed that some aftermarket thermostats have the wrong temperature rating and/or don’t look anything like the original

My philosophy is this . . . if it’s a pain in the butt to replace something, install a factory part.

Especially if the cost is as low as that of a T-stat.

@circuitsmith: “Sounds like changing the t-stat should be on the list of extras at each scheduled belt change.”

Yes, of course. But auto shops are often caught in the middle when it comes to thoughtful extras at maintenance time. Often we encounter the “educated consumer” who has gained just enough knowledge to make the wrong decision. As in “I’ve read all about the add-ons you guys do to pad the bill. My owner’s manual doesn’t say anything about replacing the thermostat so I’m just going to have you do the belt and nothing else.”

Just last week I had this conversation:
“Hello Mr. Jones. We found out the cause of the steam and overheating on your Subaru. Your plastic radiator tank has split open and is leaking coolant. Your car needs a new radiator and I recommend replacing the radiator hoses as well, for a cost of $XXX. And since we’ll have all the coolant drained and the lower hose off I suggest installing a new thermostat, it’s only another $36 to do that.”

“Go ahead and do the radiator and hoses but leave the thermostat. I’ve never had any trouble with those.”

The old saying “penny wise and pound foolish” applies to many such decisions, unfortunately.

When replacement of a t-stat is that intensive it would be foolish to use anything other than the OE if one is available.