BRN2KL

I have a 2000 XJ. 4.0L engine.

How do I trouble shoot the temp sending unit to determine if it is working properly?

Almost immediate spike in engine temp. This happened the first time this morning.

I know I need parts, I'm just trying to determine if I need a sending unit, a clutch fan, or water pump. Good news is I have a new radiator that I can drop in, but I don't think that is the problem.

Need some help!

RTorrez1

First thing you need to do is verify the temp with a IR temp gauge aimed at the t-stat housing. Are you actually boiling over or is it just the gauge saying that it is hot?

BRN2KL

Thanks for the tip.

I don't have a IR temp gauge. Only the gauge is reading hot. It has not boiled over, that has lead me to the belief that it is the gauge, not an actual engine malfunction.

djb383

If the rad cap is good and the antifreeze/coolant is in good condition and mixed at the proper ratio, coolant shouldn't boil until +/-260F however, 260F is way past overheating.

Nobody can guess if u really are actually overheating and if u r, nobody can guess the actual cause. Until u tell us what parts u have replaced/maintained in the cooling system all we can do with any accuracy is list the various cooling system components and u start replacing them. +/-$250 in parts replaces the entire cooling system including the radiator. If u replace the radiator, water pump, t-stat and hoses at the same time, u only have to drain/refill the coolant once. If u guess at replacement parts one at a time and that one new part doesn't cure the overheat, u gotta keep draining/refilling the coolant each time a part is replaced.

As suggested, a IR temp gun ($25) is handy as a pocket on a shirt for all kinds of things.

BRN2KL

Well said!

I haven't replaced any parts in the cooling system. I have maintained it by insuring proper fluid levels, and that is all.

I'm really wanting to know how to troubleshoot the temp sending unit. If the sending unit is good or checks good, then I will bite the bullet and replace the standard cooling components, water pump, radiator, t-stat and so on all so I am no refilling the radiator 5 times.

So any help on how to check the sending unit would be sweet.

djb383

To actually test the CTS, u'll need a digital volt/ohm meter and an accurate thermometer so that u can read X ohms at X temp. The efan should turn on if the connector on the CTS is unplugged. The +/-$250 for parts also includes a new CTS (+/-$30, iirc).

Pelican

I suspect that you really, really don't want to hear another suggestion that the only practical way to check the combination of the temp sensor and gauge is with an IR thermometer....

Having said that, resistance figures are available from some source, probably the FSM, that can be used with a meter to check resistance (ohms) of the sensor in a pot of water as it is heated on a stove with a cooking thermometer. If no one on the forum comes up with the figures, you can probably find them with a search on the 'net.

As respects senders (the gauge sender, not the sensor in the thermostat housing that feeds the CPU), I had a situation where temps were rising on my '93 (not overheating) at highway speeds. The IR thermometer consistently showed that everything was well within spec. I finally replaced the aftermarket sender (BWD) with an OEM unit (not overly expensive) and the gauge now tracks perfectly. This is a different setup than what you have but if you end up having to replace the sensor, it might be worthwhile to do so with an OEM unit.

djb383

On '97 up XJs, there's only 1 sender/sensor....the 1 in the t-stat cover.

Pelican

If you are referring to my post, that was my point about the OP having a different setup. I don't know if it technically correct, but I refer to a sensor that feeds a gauge as a "sender" and a sensor -- CTS in this case -- that feeds the CPU as a "sensor".

Anyway, does anyone have the resistance figures for the OP? I've seen them but I don't remember where.

djb383

I believe on '97 up the ECU signals all needles/lights where to point/when to light up. OP, r u set up to test the CTS?

Pelican

Here are resistance values and some thoughts on testing:

http://www.jeepforum.com/forum/f11/c...r-ohms-915224/

BRN2KL

I am set up to test the CTS, I believe. I have the Ohm meter, I do not have a IR thermometer. I can and will purchase ASAP. That being said if you have a step by step method, Im all ears.

Thanks for all the input guys!

Pelican

Look at post #11 in the link I posted above. For most accurate results you remove the sensor from the vehicle and put it in a pot of hot water.

djb383

As said, put it in a pan of water on the stove and slowly bring water temp up using an accurate cooking thermometer. Obviously, u won't be able to test past 212F water temp. In the second pic, substitute the t-stat for the CTS.

BRN2KL

Thanks for the input and advice guys. On a whim I pulled the dipstick, and found the coffee with cream color indicating Anti-freeze in my oil. Since I have the 0331 head, I figured my head is cracked. Good news is I have a rebuilt head sitting in the garage. I actually started the dis-assembly last night. I was working til 10PM. Thanks again for the help guys