Engine not warming up to 190

 We got a 95 Grand Cherokee with a 318 (what ever liter that is). With the radiator unblocked the engine temp only gets up around 130 and with it blocked the temp it gets up to 170.  Last night after driving for 50 min in 40 degree temps, we get home and I take the radiator cap off.( yes,I know don't do that but I had on a welding glove and I knew there wasn't going to be much pressure). The antifreeze temp was around 170 and when  started it up it started falling. Telling me that the water was not circulating. And this with the radiator 95% blocked off. Needless to say the cabin temps are not that great due to low engine temps.
   I have checked the thermostat by putting it in hot water on the stove and it opened at 190.  I have replaced the fan clutch thinking maybe it was locked up and spinning too much. Radiator cap also. Heater core has been flushed. Radiator and water pump less then 5 or 6 years old.

We have been dealing with this problem for a couple of winters now and its getting old being cold.
Please help, Thank you

Normally when this happens you have a thermostat that stays open too long. It’s not expensive to replace the thermostat, which will likely solve your problem. Most of the posts we get here are about engines running too hot!

If the thermostat is a loose fit between the intake and the housing enough coolant can by-pass the thermostat to prevent the engine from reaching 190*. Install a new, proper thermostat and run a thin bead of RTV around the edge of the thermostat base under the gasket.

I belive the thermostst is ok. I will give the RTV a try I guess, unless someone else has an idea.

There’s not much that can keep your engine running too cold other than a thermostat failing–opening too soon, never properly closing, opening at the prescribed temperature but not closing again if the temp drops.

Your engine should have a thermostat that opens at 195 degrees. If blocking off the radiator gives you a higher temp, then you can safely assume your t-stat is at fault. It’s letting the coolant circulate too soon/too much, not allowing the engine, and thereby the coolant, to reach proper operating temperature.

The way to test a thermostat is to replace it with a quality new one. I assume you replaced it when you had it out the first time you tested it, right? I’d hate to think that you’ve been running cold all this time for want of a $10 part.

When you test a thermostat in water and it opens at 190 degrees, that tells you it will open and not let the car overheat, it does not tell you that it will close against pressure. Don’t be an Idiot, put in a new thermostat. Won’t it be worth 10 bucks to tell me I’m wrong if it doesn’t work?

Over The last 2 yrs I have bought 3 different thermostats including on 2 weeks ago. I guess I failed to meantion that part in my first post, sorry. :frowning:
Anyway, After I put in the new thermosat and it didnt change anything. A week or so later I took it out and did the hot water test. I have been getting these from Advanced Auto. I think the first one might have been the cheep kind but the last 2 was the upgraded to their superstat. When I get a chance I will try the RTV. It might be a couple days becouse of my our work schedules. And oldtimer, what are you doin up at 211 am? lol.

I always recommend an OEM (from the dealer) thermostat.
A lot of the aftermarket ones don’t fit right or are junk.
There’s just no way an engine will run too cool with a properly working thermostat.

That would be the venerable 5.2L…Like the other guys say…I would also replace the thermostat…it is probably faulty in a way that cannot be determined on the stove. I always use my handheld infra red thermometer to check the block/rad and other areas under the hood for proper temp and compare the readings with the gauges in the vehicle… You can pick one of these up rather cheaply …I find mine EXTREMELY useful.

Again…just swap out that thermostat and see what you get…they’re cheap and you can also maybe buy two of them at different temp ranges…they probably make a 220 for that engine. so…

With that handheld infra red thermometer you can test so many things in many different ways…I’d buy one of those too…Harbor Freight has them for under 20 bucks…

SO…definitely install a new thermostat at whichever temp range you like…going up to a 220 wont hurt you…

!!! *** !!! ALSO Make CERTAIN to PROPERLY BURP YOUR RADIATOR/COOLING SYSTEM !!! *** !!! Your issue could very well lie there, if you have an air pocket in the system it will wreak HAVOC on many things in addition to driving you totally nuts… If and when you do burp the system…see what happens…everything will then work as it should with solid coolant and NO AIR…

.NOW…if after you burp the system you then develop yet another bubble in the system…then this opens the door on a new chapter of fun…Head gasket failure… I hope you don’t have to read that chapter of the DIY vehicle repair guide…but I had to at least warn you

If I were you…I’d buy a new thermostat right off the bat, install it (super cheap to do)…and BE ABSOLUTELY CERTAIN !!! to burp the system !!! PLEASE…I cannot stress this enough…You may even have an air bleed nipple on this system…if not, there are other ways to do this…but I cannot stress how important this is…its as important as having coolant in the radiator…so…make sure to get it right


After watching this post languish on, to me it boils down to two basic questions. Is the therostat isntalled correctly, not backwards, and is the sensor unit ok.

While I appreciate all the helpful info and suggestions let you tell you something about me. I have been working on cars since I was 14. I am 42 now. Never had any schooling on cars exept under the shadetree. I have a fairly good concept of cars. In my “many” years I have never had to burb the system. could you please school me on that becouse I do not have the the nipples to do it. And Yes the thermostat is in correctly, spring in the block. I will go to the dealer get the OEM thermostat. And put a thin bead of RTV on it and install it correctly then burb the system, as soon as i figure out how to do that. then I will let ya know. Sorry if I am sound like I am sounding like a dick but I am havin a very bad month. Oh and barkydog…you dont have to read it. Isnt this what its all about, people helpin people. I am goin for a beer. G nite guys

1 Like

Cancel the burbing request. I did a qiuk internet search and I got the answer

Burp, not burb.

Hey Madddawg, I’ve seen people here get annoyed at responses & act like twits. You’re not one of them. Hope you enjoyed your beer.

I’ve watched the thread being the curious type & it all does point to a thermostat, so we’d all be happy to know what the results are when you put in an OEM version.

Really? You have never heard of Burping the cooling system? Removing any trapped air pockets? Hmmm…you did an internet search and what did you learn?

My reply remains the same…install new thermostat and burp the system…Make sure you don’t have an air pocket. Some cars have a bleed nipple…some don’t…the ones that don’t require several heat up and cool down cycles to pull in the coolant an purge the air…

I started working on cars younger than you and am now 39…I’d position my skills between a Pro and High level hobbyist/Hot Rod type…

I’m just trying to help…Was that attitude I detected?


I have heard of burbing the system just never done it according to any book. I just basically kept adding antifreeze until I couldn’t add any more and checking often after doing any cooling system work. No that wasn’t attitude. Sorry if it sounded like it. and I did enjoy the beer or 2 Thanks

Ah…Yes… On a Honda…many Hondas, Toyotas many foreign vehicles…etc…Because they have convoluted cooling system routing/pathways (maybe because of their high mounted AIC valves) they leave you a nice little bleed nipple up high in the system somewhere…bec the system would be difficult if not impossible to burp without them…they work like a dream and I think every car should have one.

Like I said the ones that don’t have the bleed screw…require several heat up and cool down cycles…and not by driving the vehicle either…you would heat up the engine at an idle…driving with an air pocket is begging for trouble.

Well now that you…Check’d your temp with a new Thermostat… got all Beer’d up and Burp’d out…WHAT say you?

I am kinda at a stand still on this problem now. went to the dealer and they want $26 for an oem Thermostat! Parts store is like $7. I am not working much right now, if at all. $26 would by 2 or 3 meals worth of food. I may get some RTV and try what Rod Knox said. Thanks Guys

Ugh… At the VERY LEAST get a new $7 one then…

$26 is a half-tank of gas on that vehicle.

I’ve learned over the years that I can’t afford the cheap stuff and I don’t have time to take the shortcut.