00_WJ_4.0

So one of my many jeeps isn't getting up to normal operating temperature. I've done alot of work to this jeep and it runs awesome and literally, aside from some odd clunking in the rear over bumps, (thinking shocks) it really runs and drives amazing. The only issue I've had is that it never gets up to normal operating temperature. Now, I had to wire the cooling fan direct to a ignition source but that shouldn't affect anything as my old daily driver was the same way and didn't have that issue. Is it possible that the thermostat I put in is faulty and not closing? Simply allowing the coolant to always circulate?

00_WJ_4.0

dave1123

Duh, yeah! The thermostat's job is to restrict flow, keeping the engine at normal operating temp, opening and closing to accomplish this. The PCM needs to see 195* for proper fuel trim. I always use Stant Superstats because they vary the flow rather the open fully and close completely. With ones that do that, you can watch the temp gauge dive toward cold when they first open, flooding the hot engine with cold coolant.

00_WJ_4.0

Okay lol thanks. Just wanted to be positive before ripping it out yet again.

dave1123

Be careful tightening the bolts on the housing. I cracked the lower flange by snugging it too much before the top one. You would think after all the stats I've replaced over the years, I would know better. Familiarity breeds contempt!

00_WJ_4.0

Okay will do and thanks. Just want to get all the little bugs worked out of it.

blueseasons

While Living in Hawaii for 24 years I experimented with various things to help keep my engine cool while driving on the sand. My personal experience is driving with and without a thermostat made absolutely no difference in the operating temperature. All the vehicles I tried this on got up to operating temp, they did not run any cooler or any hotter. I did not try this on our era jeeps, but I did it on 2 CJ-7's (with 4.0) amongst others and the result was consistent across all vehicles. I am assuming that a constantly open thermostat will act similar to no thermostat?

dave1123

The only thing I've found is in dirt track racing, it will overheat due to coolant flowing too fast thru the radiator to give off it's heat. This was solved by using a restrictor made by taking out the valve of a thermostat and using just the ring. Engines with carbs don't seem to care if they run colder than normal. As a matter of fact, they run really good on cool, damp nights. The heavy damp air kinda packs the cylinders for more power.

Today's electronically controlled engines don't like things not being within design parameters. They'll stay in open-loop mode instead of relying on sensor feedback.

Bugout4x4

You are one of the few old farts like me who understand that coolant can flow TOO FAST through a system to actually cool correctly. Yep...that is why flow restrictors are a best seller to those not running a thermostat when racing. And there are dozens of designs.

https://pitstopusa.com/c-131774-cool...strictors.html

00_WJ_4.0

What's happening is that it's not getting up to operating temperature and it's this not allowing the PCM to go through the monitors completely. I was running it prior to the old thermostat crapping out and it was fine, untill the PCM took a **** and I had to replace it with another one out of a different 2001 4.0 grand, as well as the ignition and skim module...that got it running again then it overheated...replaced the stat and then it wouldn't get to operating temperature.

00_WJ_4.0

And I've done this with various vehicles over the years and as said, no difference that really made a difference, however, prior to the wj grands, I've never owned anything newer than a 94...I used to keep the old ones because they don't have to go thru all the B's New York is pulling with the inspection

dave1123

Yeah well.... we were running inverted 8 on a shoestring, so an old gutted thermo worked fine for us! LOL! It was my introduction to dirt racing and it was a blast!

Bugout4x4

I did some dirt oval racing for a couple years. And more recently sponsored my Dad's best childhood friend with his car. He was still winning races at 80 years old!

dave1123

Up here, they decided figure 8 racing was too dangerous so started inverted 8 racing. This is a smaller circle inside a big one. That way you only have to like change lanes to miss other guys! It was a $5 entry fee and you got a $5 trophy! Cars had to be late model stock without modifications. One guy was running a Pontiac Bonneville with factory stock Positraction and everybody tried to run him off the track! We were running a 57 Chrysler Hemi, but the thing didn't want to turn! Super fast down the back straight though! I got it up to 70 on a 1/4 mile track! Then came the turn!

Bugout4x4

Man... Traffic passing through traffic would be a mess! lol