Radiator recommendation for California Weather

One point that everyone seems to miss is obvious only if you bought one new or got an unmolested example. On both sides and the top of the radiator the cars came with a foam soft seal that conforms to the radiator and the bonnet and side bulkheads. This forms a seal that direct the airflow through the Rad and not around it. In racing I made a solid bulkhead to fit and gave it room to flex into the rad and reduce the fire risk. No flow thru Rad equal hot cat!

Also try water wetter basically a glycern additive reduces surface tension and results in more cooling potential!

Cheers

Robert

Various Models and Years
writer/ Photographer for Jaguar Magazine / Racecar Engineering

Michael, Obviously, as you say, it makes no sense to change a perfectly good thermostat, thats why we test every one we take out AND PUT IN, we do this on every car on which we do cooling system service. In this particular case he did not report "overheating" just that his "kenlowe" fan was on a lot. nor did he mention "unusually" high temperatures. In hot climates any electric fan system is going to work a lot particularly the older ones. In such climates it is essential to use a summer thermostat of 74C or 160 F. If a winter thermostat is used say an 88C/ 194F, the temperature gets too close to the threshhold for the fans to easily bring it down, a consequence is THE FANS WILL STAY ACTIVATED LONGER! As you obviously know any car cooling system gets hotter much faster than it cools. When, -in order to comply with US EPA regulations- many manufacturers made the engines run hotter by using an 88C thermostat. At the time I was with a Jaguar Dealer service department in Los Angeles. Once we were aware of the dangers associated with this higher temperature we advised owners to revert to the cooler 74C. Furthermore, on any jag V12 engine it is essential to test both thermostats, especially on the XJ series. Many an engine was lost because of a faulty left thermostat/weak fan motor, and the lack of a temperature sensor in that side of the engine, The thermostat is, argueably, the most important part of the cooling system and should never be ignored. BTW, the main reason mopdern cars use aluminium/plastic radiators is weight, they were not designed to make the car run cooler that would conflict with the aforementioned EPA targets! Regards, Jaguar affectionado and etc.

Dear Michael,

Thanks for all the advice which I will look into when the car goes in for Service at DeLongs. If it needs a new radiator I'll go for the Aluminium one. It already has an updated Kenlow Fan for cooling.

Thanks

David

Ok. Let's see if I can rephrase. There's no point in replacing a perfectly good thermostat with a "cooler" thermostat in an attempt to lower unusually high temperatures. Switching from a 180 to a 170 won't matter if you're running at 190.

Checking the thermostat has always been my first step when ferreting out an overheating problem !

I think Michael just used a poor choice of words. A few lines later did include "....unless its defective....".

Assuming its verified that the thermo does open fully Micahel's remarks make sense. If the car is running at 95??C it hardly matters if you have a 74??, 80??, or 82?? thermo, as in all cases the thermo would be running fully open and no longer a factor in the problem....so don't bother changing it.

Doug Dwyer
Longview Washington USA
1995 XJR

Michael, I was going to respond yesterday, but I thought I should wait and see what "outpouring" of response there would be to your statement, "dont waste any time examining your thermostat". I wish I had been told that 45 years ago, I could have save thousands of hours of testing, time I could have put to good use changing cylinder head gaskets! Jaguar affectionado and etc.

First a disclaimer: I am the proprietor of CoolCat, and I design and build fans and radiators.

A few points:

First of all, don't waste any time examining your thermostat. It's fairly unusual for the car to run "on the stat" with the stock components. This would mean that the gauge always reads around the center of the band. If you're experiencing overheating, then changing the thermostat won't make a bit of difference because the thermostat(unless it's out and out defective) will be fully open in any overheating condition.

Just about every car built today has an aluminum radiator, and radiator shops are quite familiar with repair techniques. Aluminum cores really can't be welded, the only possible repair is an epoxy patch: this is also true of the early 3.8 E-Type radiators, which were made of brazed aluminum plates. The difference between the aftermarket aluminum E-Type radiators and those used in modern cars is that the tanks are welded. Your local rad shop would be familiar with the radiators made for modern cars: aluminum cores with glued-on tanks. They won't have the welding skills to replace a welded on tank for an aftermarket E-Type radiator. So if a core replacement is ever needed, you would have to return the radiator either to the manufacturer, or another manufacturer of welded-tank radiators. There are several of these in the US. Another possibility is to buy a core from a rad shop, and deliver radiator and tank to a competent welder.

The stock E-Type cooling systems were far better than people give credit, and I always encourage customers to attempt repair if possible. I am especially fond of the early E-Type stacked plate aluminum radiators, which was unfortunately abandoned by Jaguar by 1963. But if you have to replace the radiator with something new, modern aluminum radiators sold for this purpose are going to give you much better performance than stock. There are technical reasons why this is the case, which I would be glad to explain if you like, but I don't want you to confuse this post with an advertisement.

There are many simple, easily overlooked areas that can cause problems with E-Type cooling. The first two things on your list should be the belts and hoses, especially the lower radiator hose. Just on principle, these should be replaced every five years or so.

Other things that can cause overheating are a blasted thermostat housing. This is a very common problem. It happens because the bypass is at both the highest temperature and lowest pressure point in the cooling system. As a result, there is a tendency to cavitate as the thermostat closes. Once the housing starts to deteriorate, hot water can circulate around the motor without passing through the radiator (http://tinyurl.com/ggqnd). The photo is a 4.2 housing, as found on late S1 and all S2 cars. On your car, the bypass will be a slot. The odds are it never sealed well, and if it's a bit blasted, it's almost a wide open shortcut between the water pump and the motor. Another problem is that the correct thermostat has a sleeve that covers the slot when open. Unfortunately, many later replacements don't incorporate the sleeve. Some folks have installed a restrictor in the bypass hose to limit flow. This may be the best solution.

The bad news is that if you have cavitation damage in your thermostat housing, you may have the same type of damage in your pump involute. Repairing this would require removing the timing case cover and having it welded and machined.

Next, your coolant matters. Contrary to the endless bad advice you will find on the web, pure water isn't a solution for your problem. The reason is that while the heat transfer characteristics of water are better, the vapor pressure is lower. In other words, it boils at lower temperatures. That's what causes the sort of cavitation damage seen in the photo. A 50/50 antifreeze mix not only raises the boiling point, it reduces surface tension. This will both reduce the tendency to premature boiling, and it will make the coolant more efficient. Summer or winter, 50/50. Long life antifreezes have better solubility than your grandfather's green stuff, so you won't get much sludge deposit. If it hasn't been done for a while, have your system chemically flushed and refilled.

Other things that affect cooling include all the usual tuning issues: timing, carburetion, wheel alignment. Anything that makes your car run less than optimally. And don't forget silly things like dragging hand brakes.

Dear William

You're probably right, I'll check it out this weekend to make sure its a 74 degree one.

David

Andrew, are you sure you have a 70 deg? I have never seen one so low. Ordinarily three were available; 74; 82 & 88. Even if you have a 70 I would test it just make sure it does work properly, this is easily done in a pot on the stove using a small thermometer. Regards Jaguar affectionado and etc.

Thanks for the advice, I have not changed the thermostat to a 74 degree one (current one 70). I'll see if that helps first, then upgrade the fan followed by the Al radiator if there is still a problem.

It might be worth doing a little more research. Most often the cooling problems are related to weak fans, not the radiator. That being said the original radiator is excellent and here in the San Fernando valley it gets quite warm -yesterday was 109! The biggest problem with alum radiators is getting them repaired, they are not something many rad shops will work on. By the way did you change the thermostat to a summer one? 74 deg. Regards Jaguar affectionado and etc.

Dear Brian,

Thanks for the advice, I'll switch to a SNG Barrat Aluminium Radiator and further update my Kenko Fan to a Cool Cat if needed.

Thanks

David

having lived through several iterations in San Antonio, TX with an air conditioned Series II E Type, the only panacea is an aluminum radiator. Better fans are also desirable. I have two Cool Cat fans and another larger fan on the stone shield pushing air in. A match held near a bonnet louver is immediately blown out by the fans coming on. At a dead stop in a traffic jam, the aftermarket A/C blows cool and the water temp never goes above the M in NORMAL.

Brian