I installed a TTO in-line temperature gauge in the Cherokee this weekend. My question is does anyone have info on the difference between coolant temperature coming out of the thermostat heater hose and actual engine temperature? I installed the in-line sensor in the heater hose about a foot after the thermostat housing.

I've noted temperatures between 185 - 201 during normal around town driving. I assume there is a bit of heat loss with the sensor being a foot or so after the thermostat housing, but I'm wondering how those temperatures correlate with the actual temperature of the engine?

For what it's worth, I installed this sensor / gauge because I just have a dummy light, which I'm still not convinced works after replacing the sender - saga detailed here. My placement of the sensor ~12" along the hose had more to do with the 3 foot cord TTO gives you than anything else.

Thanks for any info!

 

The computer uses the coolant coming out of the thermostat housing to take it's own temperature.
I don't think you would see any heat loss in the foot or so of heater hose, before your sensor. The coolant is constantly flowing through that hose while the engine is running.
Your temps are probably right on.

 

What temp t-stat r u running? What ambient temps? Running the heater? Got pics of your install?

 

I recently put in a 195* t-stat and new water pump. Ambient temp of about 55* outside today when I drove - I had the heat on "middle", so not really pumping, but it works quite well. I'll try to post some pics perhaps over the holidays (my camera, unfortunately, took a plunge to the bottom of a harbor in Spain).

Fire - thanks for the feedback. I know I do need a fan shield (mine cracked into a few pieces) as well as possibly a new fan clutch (though the fan doesn't free-spin when the engine's off). However, it'd be good to know it's at least hovering supposedly where it's supposed to (~210*-ish from what I've read).

 

In 55* ambient and the sender located where it is, 185-201 sounds about right to me with a 195 stat. This time of year, our ScanGauge displays 175-185 (180 stat) while using the heater. U may not see 210 'til next next summer when running the a/c. I never have understood the statement "it's supposed to run 210". Why would it run 210 under the driving conditions u described. Sounds like all is good to me.....right where it should be.

One thing u must remember "Coolant vs Engine Temp".......different areas of both the block and the head will have "hot" spots and "cold" spots and what the gauge is displaying is the temp of the coolant after those "hot/cold" spots of coolant have mixed together and coolant exits the motor. The coolest part of the motor will be the front of the block as that's where cooled coolant enters the block. Coolant then travels to the rear of the block (picking up heat) and exits the rear of the block. From the rear of the block, coolant travels up entering the rear of the head (picking up more heat) and exiting the motor out the front of the head. On average, the coolant exiting the head will be the warmest/hottest. T o complicate matters even more, the XJ (and virtually all water cooled motors) have 2 coolant flow "loops"......the bypass loop and the radiator loop. Coolant always flows thru the bypass loop (motor running) and coolant may or may not flow thru the radiator loop and when it does flow thru the radiator loop, it flows at variable rates.

 

I would make sure and get at least a used fan shroud, if you are not running one.
Is it just cracked? or is it gone completely?


You need that shroud on there to properly pull the air through the radiator.

 

Thanks for all the info - I suppose I've read somewhere that the 2.5 XJ engine is "most efficient" at 210* somewhere and that's what was behind my "supposed to" comment. I wasn't sure if the variability I was seeing (185 - 202) was normal, as I haven't known the engine / coolant temp on my cherokee in the 10 years I've owned it - but it makes sense given how the thermostat works and all. It's good piece of mind the temp isn't shooting way up, after my replacing the water pump and thermostat (i.e., glad I got it right). Oh, and no A/C. Now, if I could just solve that damn serpentine belt chirp (new belt & tensioner since the WP / T-stat change and still chirping)!

 

Thanks - yeah - the top 1/3 of the shroud is basically gone, but the whole bottom and side is still intact. It's on the short list.

 

With regard to the 2.5L being so called "most efficient" at 210*, I'd bet that is just someone's opinion on a forum with nothing to back it up.

It will be interesting to see your numbers next summer, even without a/c. Keep us posted with your observations. It's always interesting to see/hear how a aftermarket gauge, especially a digital gauge, shows what's really going on.

 

As far as the chirping belt................
You should have a manual tension adjustment on there.
Probably just needs a bit more tension.
I always "run-in" a new belt, and go back and re-tension after a day or two.
They have to wear in to the pulleys for a short time before they will settle into the grooves.

 

Thanks - started a new thread about it here, but the sucker is tight. I may try tightening up a bit more, but I'm somewhat concerned about too much tension on the belt. Pushing hard right by the tensioner I can get it to deflect about 1/4 - 1/2".

 

I think the rule of thumb is 1/2" of deflection per foot of belt length......

on your 4 cylinder, the longest section should be from the alternator, down to the crank..........That section should deflect about 1/2"-3/4"

 

There's really no single "actual engine temperature" with which to compare. Parts of the engine itself will be considerably hotter than your coolant, and the temperatures within the engine will fluctuate. We monitor coolant temp because it's the easiest and most reliable measure of whether the engine is operating within the normal temperature range.

You can also monitor oil temperature and exhaust gas temperature to get an idea of what your engine is doing. I monitor oil temperature in my Subaru using Torque (and will probably do the same with my XJ if I ever get it back from the body shop). Depending on the kind of driving I'm doing, the oil temps in the Subaru can vary from 200° to 225°, while the coolant temp sits rock solid at a nice, comfortable 190°. I would expect a similar range of oil temps in the XJ.

I'm not sure if your year has an oil temperature sender, but I think the OBDII trucks do. EGT is something you have to add aftermarket to most naturally aspirated vehicles, and there's a lot less reason to do that unless you're adding a turbo.

The "normal" temp on the dash gauge for the later model years, where the needle is straight up, is 210°. My 2000 normally runs at 210°, but if I'm not mistaken there is variation in what is "normal" for the various years of manufacture.

 

U've got the "best of both worlds" set-up now.....an accurate aftermarket digital temp gauge displaying in 1 degree increments that's not "rigged" by the factory to point at 210 AND a bright red light that will really get your attention should something go wrong.

I've seen several posts over the years saying something like "I did not notice the needle was in the red"......I've never seen a post saying "I did not see the bright red light". LOL