Jeep Grand Cherokee - No (limited) Heat From Heater

Not a clue. The only thing I've run across remotely similar is a low temp reading with a boiling hot radiator. That one turned to be a very low coolant level, but your problem seems different since you have physically verified that the engine doesn't seem hot. Might check fluid level anyhow. It's cheap.

Thermostat is either missing or stuck in the open position.

That has happened to my car (20 years old) twice now in the last two years just after the weather gets cold and they switch the petro formula back to the non summer mix. Don't know if that is a coincidence, I suspect it because so many other problems with my car also seem to be related to the change in ethanol in the mix.

Thermostat got stuck in the open position and was sucking all the available fluids dry as the engine overheated. So far I've been lucky and it has only been the replacement costs for the thermostat. I'm sure it is also shortening the life span of the engine.

Symptoms were it taking more than 20 minutes to warm up the car's heater in the morning, going through quarts of oil each month, and overheating when idling for more than a minute.

CD, the thermostat is a cheap enough part that it is worth changing out as part of your process of elimination.

Okay, all good input.

Let's see . . . yes, it's a low cost option (oops, no cost really . . .) to check the fluid levels - and we know the fluids are all solid.

I'm not going to even address the confluence of this "problem" coinciding with the seasonal change in the ethanol ratio mix in the local fuel supply - as there simply cannot be a connection between the engine fuel supply and the cooling system. This is apparently just a fun-loving extension of the correlation without causation argument (sort of like firemen can always be found to be present at fires, therefore firemen cause fires). Grade = F -

From having experienced a failed thermostat twice, I think I know what that looks like. It looks like an overheated engine when water doesn't pass from the water jacket, and back through to the radiator to be cooled. I remember my dad's advice that when the thermostat fails in the closed position, you can sometimes mitigate the overheating of the engine, by running the heater at the highest fan speed, as the heater core will actually act as an auxiliary radiator, on the engine side of the coolant loop (that was a neat tip, thanks dad - although it's not too much fun on a hot summer evening . . .).

Not sure about the origin of the speculation about a "missing thermostat", since how does the thermostat "get out" of the coolant loop (?) - and kidnapping a thermostat for ransom, seems like science fiction. All of that light-handed rhetoric aside, talking this through (more exactly, typing it through), is helpful, because I was trying to "visualize" what [harm] happens when the thermostat fails in the open position. As I thought through it - what happens may be exactly [the symptoms] we're seeing though. In that situation, the water pump circulates water almost continuously through the water jacket, and the water never really stays in the water jacket long enough to get up to a temperature that allows heat to transfer from the heater core (or to be registered on the temperature gauge). I never thought why the thermostat is really necessary, but it's actually there to make sure the water does get up to a certain temperature. I think the low-cost first step solution is to replace the thermostat - and see what happens (since it's probably the original thermostat from when the vehicle rolled out of the factory . . .).

if you have never replaced the radiator, I would start looking into it.

after 15 years it probably doesn't flow as well...

also check for a heater valve. jeep used to like using them.

Yikes . . . I was feeling optimistic about a relatively simple repair later this afternoon, and now you've tried to take me to a "dark place" regarding a radiator replacement (which can't be too much fun in an unheated garage in November/December). I think the radiator is in pretty good shape, as I've been pretty religious about coolant changes over the years - and compared to some radiators I've seen, this one looks clean enough to drink out of (exclusive of ethylene glycol being not a recommended mixer in a cocktail . . .).

Good tip on the heater (core) valve, as I was unaware of that - although the valve, if there even is one on my Jeep, is a pretty simple, vacuum actuated mechanism, that operates by default in the open position. Not sure I know/understand the purpose for the valve, but I'll keep that in mind. My spider sense is still leading me back to the thermostat, given that radiator temperature gauge is barely reading any temperature increase, and the radiator, including the metal pressure relief cap, are only perceptibly warm to the touch, after driving a fair distance - where you would assume the radiator (and cap) would be pretty hot at that point (based on past history).

Okay, a trip to a "dark place" on the replacement of the thermostat this afternoon turned out not to be necessary (thank goodness).

This turned into about a 20 minute repair - if you don't count the need to go back to the auto parts store after discovering that when you buy a replacement thermostat ($3.99), that purchase no longer automatically includes the mandatory replacement thermostat gasket (yikes!). This seems totally looney to me, since the gasket(s) on these kind of replacements are automatically assumed to be necessary, since salvaging an old one is like trying to repair a balloon that's been popped (it's hopeless). This was made all the more frustrating, since the location of the original thermostat purchase didn't stock the needed gasket (". . . that's a dealer-only part"). Ugh! Thankfully, another national auto parts chain stocked the exact right gasket ($1.99) - thank God, since the old thermostat had already been pulled, effectively destroying the old gasket . . .

Despite one other slight misstep (Note: Remember to install the new thermostat before you reassemble and bolt-in the thermostat housing). After recycling the captured coolant, and firing up the now-repaired Jeep, the temperature gauge quickly reflected the proper operating temperature - and more importantly, the heater was now circulating cozy, heated air through the passenger compartment.

An examination of the old thermostat confirmed exactly what we suspected - that the thermostat was stuck in the open position.



So for roughly $5.98 (plus tax), the problem appears to be solved - just in time too . . . since cold(er) weather is being predicted for later this week. Thanks for all the good input, and in keeping my diagnostic logic on-track.

I was reviewing estimates for what the replacement of the coolant thermostat might have cost, if the service had been performed locally by other providers, but the estimate seemed almost unbelievable.

First, I'm not sure how this could be estimated to take close to an hour to complete, since it realistically took me right around 20 minutes (not counting the "parts delay" periods). And $80-69 per hour? It makes me wonder whether I'm in the right line of work. And somehow, I even managed to beat the parts cost estimated - although I captured and recycled my still good, radiator coolant. Guess that might have boosted the cost if that had to be replaced, and I assume most repair places would have "insisted" on replacing the fluid - even if you told them you'd flushed and filled the radiator with new coolant the weekend before.

The local shop I use is maybe $10.00 higher than that. They can still get under dealer total labor by about 25%. Those flat rate manuels are sometimes good for the dealers, and sometimes not.

Like you, I am disappointed to hear that the gasket is no longer a part of the replacement thermostat. I have never once heard of the old one being reused, which is mostly academic as they are usually destroyed in the process of removing the flange.

HEY I NEED HELP I JUST REPLACED MY THERMOSTAT IN MY 1996 JEEP GRAND CHEROKEE BUT IT SEEMS THAT MY HEAT IS STILL NOT WORKING. WHAT DO U THINK THIS COULD BE AND HOW COULD I GO ABOUT FIXING IT.

Sure, I'll try.

First, a couple of diagnostic questions. When you pulled the old thermostat, did it look as though it was stuck in the open position? Additionally, after you replaced the old thermostat, did your temperature gauge reflect a coolant temperature in the range of what you would ordinarily expect to see? If the answer to both of these questions is yes, then I'm unsure what to suggest. But you say, the heater is still not putting out any heat? I think we'll need some more diagnostic "data" from you, but I'm still willing to offer other things to look at - and I'll assume others will weigh-in as well.