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Gold Miner 09-10-2013 12:19 PM

Running Too Cool All Of A Sudden
2002 4.0L, Auto, 3sp
Normally runs at 210 or just over the 210 mark.
Today she won't get warmer than 150-160 (according to the dash gauge).
No CEL, will blow heat, no other symptoms... running well.
Coolant system full, sealed, and burped.

I'd like to nip this in the bud.
Thermostat, right?

Imped 09-10-2013 12:28 PM

My first guess was the thermostat is stuck open. That sounds like about the right temp for that as well.

Gold Miner 09-10-2013 12:37 PM

That's what I'm thinkin'. Good place to start anyway... Carquest brand thermostat acceptable? Or is there a magic thermostat brand out there that we all like to use?

Holton345 09-10-2013 12:53 PM

Do not get a parts place thermostat. I have yet to see one with the bleeder hole. Go to a dealership. Mine (last week) was actually two bucks cheaper than the one I bought (and returned) to AutoZone. (The AZ one lacked the bleeder hole.)

The bleeder hole needs to be there, and it needs to be oriented at 12:00, straight up.

And it *must* be a 195 model. So if you find a parts store thermostat for our beloved 4.0L engine and it has the bleeder hole, do not get one that is "high performance" or that opens at 185 or whatever. 195 only! ;-)

This is a part of a critical engine system, so just get OEM at the dealer. It is not expensive at all. However, they might have to order it. They have to order just about everything for my 2003, of course, but actually had the thermostat in stock. Maybe the JKs use them, too? Hmm...

Big Sarge 09-10-2013 12:56 PM

a 1/8" hole can be drilled into any thermostat that does not have the burp hole. Stant is a very good choice.

Gold Miner 09-10-2013 12:58 PM

I'm about 70 miles and two mtn passes from the nearest dealership.
I guess I can have Carquest order one from a front range dealership if it's that big of a deal. They have guys that run down the mountain every day for OEM parts. Will probably cost more and have to wait a day though.

Gold Miner 09-10-2013 12:59 PM


Originally Posted by Big Sarge (Post 4449137)
a 1/8" hole can be drilled into any thermostat that does not have the burp hole. Stant is a very good choice.

thanks sarge!

Gold Miner 09-10-2013 01:48 PM

I went to the local Carquest and they had two thermostats in stock. Both Carquest brand and 195 degree. One was listed as "economy" and cost about $4. The other was listed as "premium" and cost about $8. Neither had the hole and they both looked identical.
So... their parts guy was already on the road down in the front range (Denver area) and I had them add an OEM Mopar thermostat since he'll be going by the dealership today.
$22, that's expensive. It'll be here in a few hours.

Big Sarge 09-10-2013 01:54 PM

1 Attachment(s)
yeah I would have not paid the $22. All you need is a 195 t-stat and drill the hole like this

Holton345 09-10-2013 02:47 PM


Originally Posted by Big Sarge (Post 4449137)
a 1/8" hole can be drilled into any thermostat that does not have the burp hole. Stant is a very good choice.

I had not thought about that. But I do seem to recall one of Jerry Bransford's posts showing how to do this. But that will not have the little floating "valve" piece in it. Also, the "real" t-stat was two bucks cheaper than the AutoZone one when I bought both two weeks ago. I am sure that this will never, ever happen again, the dealer having the best price. HAHAHA!!!

Holton345 09-10-2013 02:51 PM

$22? $8?

Where I live these exact same parts are dealer $13 and parts store $15. I wish they would be more consistent in their pricing...

Gold Miner 09-10-2013 04:02 PM

Pretty sure I'm paying a $10 delivery charge as part of the $22 for the OEM, I expected that.
really no big deal

Gold Miner 09-10-2013 05:04 PM

Just got the OEM in and this is what it looks like. It has the hole with a passive brass pin going through it. I'll install it here shortly.

Gold Miner 09-11-2013 10:53 AM

Just a quick follow-up.
Success! Thermostat was indeed the problem. Upon replacing it temps have returned to normal.

Vesp 10-30-2013 09:17 AM

I'm having what seems to be the same problem with my '01 Wrangler. Temps low, lukewarm air blowing.

I'm starting to teach myself how to take care of my own vehicle, and am uneducated. So the question is- How do I get to the thermostat to change it? It looks like I need to remove the fan behind the radiator, But I'm not sure. The videos I've found online conveniently skip that part...

bardb 10-30-2013 02:23 PM

How To Change the Thermostat in a Jeep Wrangler - YouTube

Pretty straight forward. The replacement in the video didn't use a bleeder hole and didn't mention torque specs other than 'tighten to mfg specs'. Not sure on your Jeep, but my 99 is spec'd for 15 ft/lb. Mine loosened after a couple of drive cycles, so check it regularly until it no longer backs off.

hYJacked 10-30-2013 02:33 PM

Also probably worth investing in a DIY repair manual if you are serious about educating yourself. Youtube is great and all, but can't always replace a professional manual.

valentine1210 10-30-2013 02:36 PM

My 2003 2.4l seems to be staying around the first smaller dot on the gauge maybe a little higher but normally she is right at 210. Now that it's winter I figured it was just the colder weather but could it be that my thermostat is stuck open

Vesp 10-30-2013 03:56 PM

Bardb- that's the video I've found. It looks like he's already taken the fan off, or there's more room than I think there is..

hYJacked- I agree! I'm on the lookout for a cheap one, but until then, gotta use what I can get to! :-)

Thanks for the response both of you!

bardb 10-31-2013 01:03 PM

I don't recall removing anything other than the hoses and the two bolts. But you'll figure it out in short order.

hambubba 10-31-2013 01:39 PM

You can overtighten the housing until it cracks. "just tight enough" is the rule here - really snug. You have to check it for leaks when you start it up, but tightening and hearing that "kkkkkk!" sound? Been there a few times.

SpaceCase 10-31-2013 07:41 PM

Haynes repair manual is the way to go. Can get them at Canadian Tire, not sure where in the states though.

Gold Miner 10-31-2013 07:47 PM


Originally Posted by bardb (Post 5788706)
I don't recall removing anything other than the hoses and the two bolts.

Correct. That's it..... easy breezy. Just make sure you get an OEM replacement thermostat (and gasket).... or drill an 1/8" hole in whatever you get to compensate as Sarge suggested earlier in this thread.
I got the OEM which already has the hole with a brass one-way valve in it.
Everything's still functioning very well with the cooling system.

Vesp 11-06-2013 04:18 PM

Thanks all for the info! Had some issue removing the old gasket, but as soon as I got that done, everything went smoothly.

And yeah, there was just enough room behind the fan to work.

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