I have a 1988 Jaguar XJS and I live in the Dominican Republic which is a Caribbean country. My jaguar almost always maintains the temperature very very high, it reaches the top where the H is, so I don't know whether to cancel the fan clutch with an aluminum radiator or if the thermostat is opening very late, I don't know what they recommend I do to keep it very cold because I don't have air conditioning installed and I don't want to imagine the temperature it would have with air.

 

Start with the basics. When was the last time the coolant was flushed? You dont need upgraded parts, the original parts work fine. It shouldnt be that hot, something is wrong,

 

It's fairly common with older V12 Jaguars that the front of the radiator is blocked. All sorts of debris gets pulled in-between the radiator and condenser and that blocks the airflow. With the car idling and the hood closed, you should be able to stand beside the right side of the car near the front of the door and feel a strong flow of air coming from under the car. If you can't, then either the radiator is blocked or the fan isn't pulling enough air.

The only way to completely clean the front of the radiator is to remove it from the car. There are no shortcuts here, it must come out.

While the radiator is out, check the thermostats. Most of the ones specified for the XJS are wrong and don't close off the bypass. This is critical, if the bypass isn't closed when the engine warms up, then the coolant circulates with the block and never goes to the radiator. Make sure that the thermostat opens to at least 42mm when placed in a pan of boiling water. See here for a photo of the distance: https://www.jaguarforums.com/forum/x...8/#post2725628
If you don't get 42mm, replace the thermostats. There is lots of discussion here about suitable parts.

If I was wanting to keep a V12 cool, the things I would address in order are:
- Remove the radiator and make sure the fins are clean. The space between the AC condenser and the radiator can collect all sorts of leaves, grass, etc that block the radiator.
- Proper thermostats
- Proper fan clutch
- System bled completely

Then I would move on to smaller stuff, like making the sure the ignition timing is correct, fan shroud fits closely, aux fan working etc.

 

Have you verified the temp really is high by using a handheld infrared temp sensor?

Upper radiator hose, radiator inlet fitting and outlet from head would be a couple good measurement locations.

Doug

 

You fill the radiator not with the radiator cap on the radiator but the 2nd cap.
If you have been filling it at the radiator it’s not full of coolant. Typically you have to raise the car up to get the radiator completely full.
2nd. 50-50 distilled water and antifreeze ( changed every 2 years).
3rd. Check the timing on the car. It’s really hard to do because the timing marks are on the bottom.
What happens is the distributor advance weights get frozen up getting the timing off.
You can’t feel it because of how powerful that V12 is and how smooth it runs even with the timing off.
The owners manual tells you to oil the distributor. Except nobody ever does. Hence the overheating.
An easier way to check? Remove the distributor cap. Grab the rotor and twist it. If it moves smoothly and snaps back on its own , that’s not the problem. If you can’t move it or it’s really stiff that is the problem.