Engine not getting hot enough

My recently purchased '90 XJ 4 liter does not appear to be reaching its operating temperature, even after considerable driving. Short of checking to see if it really does have a thermostat in place, I've done electrical tests on all the sender units and they seem to operating within spec. Can anyone suggest anything else I could check (apart from the thermostat)?

The only real culprit would be no thermostat or a thermostat stuck open. Even then, I think it might warm up eventually; you know the warm blooded nature of a stock 4.0. If you have checked teh sending unit, it would be a thermostat. I believe there is an old timer's trick to checking but can not remember it off the top of my head. I think you sqeeze some hoses and resistance or the lack of it will tell you if the thermostat is open. Others might know.
BSD

A 4.0L should operate with the needle on the gauge pointing striaght up -- about 210 degrees F. However, the factory gauge isn't highly accurate, so it's better to confirm before assuming there is a problem.

There are a great many people who think that the correct temperature for a 4.0L is "too hot," and they "fix" it by installing a lower temperature thermostat. The OEM t-stat is 195 degrees, and that's what should be in there. Many people use a 180 or even a 160, and then wonder why their fuel mileage is terrible.

Keep in mind that on a '90 you have two temperature senders -- one at the back of the head for the gauge (or idiot light), and one low on the driver's side of the block for sending data to the ECU. There's a third in the driver's side radiator tank to control the auxiliary fan if you have one.

Hi all, thanks for the responses received so far.I've checked all the sensors so far and they all seem to be within spec. The biggest giveaway is that even after a long run one can still hold the radiator hose in you hand quite comfortably (as opposed to if it were running at normal temps you wouldn't be able to grasp it.). I've ordered a new thermostat and will let you know of the outcome when I've had a chance to put it in.

My 93 when i got it, on a winter day, wouldent even get hot enough, even after a long drive, to make the gauge read, or the heater work. It would barly make 120 on a summer day. Finally pulled the t-stat out, and it had come apart. Amazing how cold it would run with no t-stat.

Yeah I've been keeping an eye on mine for the past six months, it warms up to the 210 then the t-stat will open and you can watch the needle go back down. I've been hoping as the weather heats up it will maintain a higher temp but even in 80 degree weather it does it, unless I'm wheeling slowly and climbing hills and whatnot.