Hey all, so my engine is not reaching Operating temp consistently. It is running cool particularly when it's cold out, and the heat is working so so. The thermostat is new, as are all of the cooling system parts with the exception of the heater core. The heater core was in this Jeep when I did the build, and I have no idea when it was last changed, if at all. Thinking I need to flush the heater core out, but I am still a little curious about the engine not reaching temp. Should I swap the thermostat again? This is the third thermostat that would have gone bad if that is the case....

 

What do you think operating temp is and how are you determining what temp it is running at?

Did you check the thermostat before installing?

 

Operating temp should be 195-200 I'm pretty sure. I am determining the temp using the in dash gauge, and I did not test the thermostat before installing.

 

iirc normal it is 195 - 210

And it is usually running lower than that? Does sound like a thermostat issue, maybe. You could pull it out and check it.

Heater core is easy enough to flush too. If you are not getting much heat, could also be a heater valve issue. Forgot what vacuum controls on that, but it does have a vacuum line that should be attached.

 

Yeah it is usually running around 150-160, but it has gotten to 195 a few times. The heat works well when it gets to temp, so that's why I was thinking of flushing the heater core, plus the body has 250K on it so probably wouldn't hurt to do it. Where is the heater valve? Under the dash? I wouldn't think that is it because it does work well when the engine gets up to temp, but I should probably have a look just to be safe.

 

Oops, if yours is a 2000 it might not have a heater valve. But trying to flush that core should tell you if it is flowing OK.

How long is it taking to get to temp?

 

Ok. Yeah thats what I figure. I may get another thermostat just to be safe, and test it in some boiling water before I install it. I have a racing thermostat I was gonna put in in case I ever wanted to chip it, but everything I have read said that running it that cool ( I think the racing thermostat is set for 180?) is horrible for you MPG, and not really necessary.

 

Yes, you need a 195 in there.

I just replaced my radiator, hoses, and thermostat and am almost always running at 195ish. Would like to check that closer with a multimeter or something, just not in the cards right now. The first thermostat I got for it failed testing, Rock Auto gave me a refund and didn't want it back either. Got another at O'Reilly and it seems to be working fine. Takes me a little over five minutes of run time to get up to thermostat opening, and it stays at 195 almost all the time. The old replacement radiator and factory installed thermostat were running about 200-205 all the time.

Note too, when I flushed and changed coolant about a month ago it all came out clean, just a little bit of scale came out of block, but that copper/brass radiator still failed.

 

Yep a 195 is standard... that's also what I put in mine when I redid my cooling system about a year and a half ago.
I don't know about on yours, but mine always indicates right about 208 at full operating temp. any time of year and I'm in Arizona at above 7,000 ft. I did a heater core flush recently was in good nic. and also pulled out the 20 yr old stock radiator and put in a nice desert rated high flow replacement....mainly to ward off the overheating issues these old XJ's are known for.
With a 195 in yours.... what do you normally get indicated on the dash? Just curious.

 

I have you checked the temp with one of those IR guns?
I am pretty sure you will shoot the thermostat housing if you do.

 

Everything I described is from reading the dash gauge. Once it gets up to 195 ish from guesstimate between the lines, and when it opened in hot water on the stove, it stays there. Only rarely does it creep up near top center.

Old radiator was a replacement in 2003 or so. Brass/copper and iirc, 3 core, and factory thermostat. New one is 2 core brass/copper. Has been so long since last replacement, I don't remember what it was reading new.

 

What brand t-stat are you using? Cruiser is pretty adamant that you should be using a Mopar for best results. Also did you replace the radiator cap with the new cooling system parts?? It's an important functional component of the system.

Also, you shouldn't trust the gauge alone - hit it with an IR temp gun and see if it's in line with the gauge. 150 is real low and would result in really poor engine performance. On a 2000 the CTS feeds the gauge and also the computer. I would definitely test the CTS to make sure it's reading correctly.

A perfectly running Jeep I6 should warm up pretty quickly and read a steady temp around 205-210 when fully up-to-temp. Visually, this presents as the gauge needle a hair to the left of the 210 mark. Again though, that assumes everything is working perfectly and readings are accurate.

 

your gauge reading may be reading inaccurately is one thing... but not getting any heat out of the vents may as simple as the heater core needing a flush. there are lots of videos of how to do this on youtube and it's a super simple process. One caveat is to be very careful about the pressure of water you are shooting through the hoses and core. If it's an the original heater core, too much PSI can cause it to fail during a flush. Not a problem you want to create if you know what I mean....

Other issue is the gauge reading correctly... you can 1.) test it with an IR gun to get an accurate reading, and 2.) you may need to change the engine coolant temperature sensor, as well. Super cheap and simple fix that may get your gauge on the dash to read more accurately.

 

Yeah I have watched a few videos on it, think I will turn the regulator way down on my compressor when I do it. I have already swapped the coolant temp sensor when I went through the cooling system so I am pretty confident it is working as it should

 

I'm having a similar problem but my temp (at least the dash gauge) seems to be fine as it's around 200. My issue is it seems to take longer than it once did to heat up and once it does it's okay but if I stop at an intersection and have to sit for awhile it starts blowing cool air. Once I start moving again it begins to blow warm air.