1995 XJS 4.0 / my fan runs as soon as the car starts. Is it supposed to cut off at some point or always run? Is there a thermostat control on this one or is it simply direct drive. The car runs almost too cool when at highway speeds. It also takes a very long time to reach a driving temp.
I am going to buy a new thermostat as well, a 190 F.
Thanks.

 

If it is about the mechanical main fan, it always run. The fan clutch is for just adjusting the speed, it can't entirely cut the rotation.

If the thermostat is sound, the coolant can't go through the radiator until it is warmed up. So it won't be a problem whether the fan is running or not, because the fan is there for to cool the radiator.

So I think replacing the thermostat will solve the problem.

 

Thanks for that. I assume the thermostat may be stuck open, causing the long warm up time. My concern was that the fan may be running full speed at highway speeds, causing too much cooling as well as sapping engine power.

 

I recently replaced my thermostat, since it seemed to be stuck in the open position.

How did I know? My car couldn't get warmer than 170F on cold winter days. Since I've replaced it, getting to 190F is no longer a problem.

I have a 96. It's very easy to swap out the thermostat. You'll lose a little coolant, but not much.

 

Thanks Vee, I am for sure swapping out the thermostat. It seems stuck open on mine as well. If not, it is a cheap precaution nonetheless. Coventry West has the exact part for $17.50.
I am still not sure how to check if the fan is running wide open at highway speeds instead of slowing down.

 

Try to spin the fan (with the car off and keys out of the car please) and see what happens.

If you can't spin it, that's bad. It's seized.
If it spins more than two complete times, that's bad too. It's slipping.
If it spins about one to one and a half times, it's fine.

Basically if there's a fair amount of resistance to spinning the fan, you're fine. Anything else, and it's probably shot.

I'm almost positive that the problem lies within the thermostat. A failing fan clutch would lead to higher temps, not lower, since the fan isn't needed to cool the engine when you reach speed.

 

Thanks Vee, going out in a few minutes to look it over in the parking lot. Good reason to visit the Jag during a work day!

 

100% agreed with Vee.

Jimbeaux,

if the fan clutch is failed, for instance if it is seized, it will run at highest speed at all the time as you said.
But it doesn't cause overcool if the thermostat is doing its job completely. As you know, it is called "radiator cooling fan," it leads the wind through radiator and cools the radiator, not the engine itself.
So when the thermostat is completely closed and the coolant doesn't go through the radiator, the coolant won't be cooled down no matter how fast the fan runs.
So I also suspect the thermostat is out of order.

 

Napa sells the fan clutch for less than 100 dollars. This is a consumable, high wear part that should be replaced anyway IMO. If you haven't replaced it yourself go ahead and do it.

 

Check rockauto.com and you will find a clutch around $30. I once installed it without problem.

 

Evidence supports both of you here. I went out and spun the fan, about 3/4 turn and stopped. I suspect the thermostat is bad as well (stuck open actually).

 

Better stuck "open" then "closed"!

 

Oh but yes!!!

 

The XJS calls for a 190 degree F thermostat. Most available here are either 180 or 195. Which should I go for? I think the 195.

 

I found it rather easy to find 87C and 88C thermostats.

Try RockAuto, eBay, etc.

I believe I am running an 87C thermostat made by Behr. Its the OEM thermostat for a Mercedes, so I figured it would work in the Ja-a-a-a-ag.

Part# W0133-1630998

Paid less than $25 shipped.

You may require a gasket. I did. Part #NBB2217AC. I got it from eBay for $6 shipped.

 

I see Coventry West has one that is 190 F. However, I needed to get one this weekend because I have time to install it. If I am limited to 180 or 195, I think 195 is the way to go. Which would you choose?

 

I'd go 195F

 

Just found a 189 F Behr at NAPA. Getting it after work. Thanks!