Series 3 E Type V12 Overheating Fix(es)

They’re also designed to have some hysteresis, meaning they don’t react instantly to changing temperature. Otherwise, the thermostats would be snapping open and shut and regulation would be poor. Most of the travel should happen just after initial open, but max may not happen for ten or twelve degrees.

Something is still off here. Flow is proportional unless the the thermostat is fully open or closed, so even if your thermostats were a little off, it doesn’t explain why your radiator is cold. Waxstat is usually a reliable brand, and even if one failed, you should be getting flow through the other side. Even if the thermostats were only partially open, you would still have flow to the radiator. But it sounds like you are getting almost none.

Modifying the thermostat is not a solution. The two poppets are driven by the same wax motor. If you end up jamming the bypass, the main valve will also be restrained. Many of these cars end up with single poppet thermostats for one reason or another, and still manage to run reasonably well, even though the bypass is unrestricted.

Rick I think you’ve checked everything. There could have been air in the system for the initial boil over or too much coolant.

Those infrared thermometers are very handy but they do have two sources of error. One is the infrared heat signature, emissivity, varies mostly according to the color of the object being measured. I think black radiates the most heat at a given temperature and white or shiny silver the least. The other is they measure average temperature over a window which increases in size as you get farther away from an object. The laser is just a pointer that shows you the center of that window. (Except it is offset as you get closer. so maybe that’s a third source of error. )

I’m just trying to be encouraging. I think you have less problem than you think you have.

Rick here’s what I would do.

I would run tests with 100% distilled water. $0.89/gal nontoxic. The boiling point is a little lower and the latent heat is higher than coolant mix so you get a little more warning. Put a few extra gallons in the boot.

I would have 2 independent temperature gauges measuring the water outlet temperatures. Depending on your pressure cap you don’t want to go over 230 F. But start a little lower say 210.

Then drive it and try and get it to boil over. Boil over is defined by water hitting the pavement. If a little water comes out it might be slightly over full. If a lot comes out but only once it was probably air. Obviously if it boils over every time something is wrong.

I think you are very close to working this out.

It wasn’t on a Jag, but the one time I struggled with overheating was when the distributor advance wasn’t working.

Great info folks. I’m working on it. Will verify the mechanical advance is working and will set timing at a more advanced setting. I have disconnected the vacuum pot, for now. The car has the SN Barrett dizzy. I will run it on water to do some more tests. Cheaper, non polluting. I have been bailing out before full boil as I see the temp suddenly moving to the hot end of the guage. I’ll let it go to see what happens. Rick


Rick, I hate to sound like a broken record. You said you flushed water through the radiator, and it appears free flowing. Did you also flush through the block and all hoses to see they are clear and free flowing? If you did, sorry I missed it. If you did not, I am not insisting that is the problem, but it is a possibility.

This sounds like a prime candidate for the Lutz mod. Highly recommended!

I have not seen specific info on the “Lutz” mod. I would be interested, except…. When I advanced the timing on the new distributor, the temps dropped. More, the “modified” thermostats do work and redirected the coolant through the radiator. Now, with the fan on, the temps remain in the normal range. I drove around doing errands in 80 degree weather, no overheat. Until…… the fans quit. This did not result in a boil over. Just higher temps. I have chased down the fan relay problem and Am making appropriate adjustments. These new fans spike about 37 amps when they start. Then drop down yo-yo about 24. The cycling of this circuit burned the relay. I have checked. The relays are rated at 30 amps. I am seeking a higher rated relay for this circuit that will retain original wiring configuration and appearance.

I have learned a lot about this cooling system. Soon, I will feel like an “ expert”. Experience is the greatest teacher. Driving around in this beauty was quite rewarding. Rick

So your “upgraded” fans were not necessary and are in fact, a problem. I would stick with fans that draw less current.

There is plenty about the Lutz modifications in the archives. There are pros and cons to it.

kind regards

Can you post a photo of the fans? You can use a DIN-style (“Bosch”) relay in place of the Lucas relays. These are available in high amperage ratings. Is your otter switch working?

I replaced the original fans with high output modern ones many years ago. I believe the brand was Scotts bought from XK’s IIRC. I wired them using the original relays which failed twice, once causing a boil over. Replaced with a solid state relay and never had another problem

A place to start.