Overheating Gremlins

Ok, I'm an idiot and quite a bit embarrassed...

First of all, thank you all for your feedback and I hope this thread was at least somewhat educational for all involved.

Remember when I said that the fan was blowing in the right direction? Well, I was mistaken. I took a closer look at the blades before I fired my car up the other day and verified what direction it should be turning. After I warmed the car up and the cooling fan came on, I could immediately tell it was moving in the wrong direction. I swapped the leads and it now works beautifully. I took a drive last night in and around my subdivision in 85+ degree temperature and the gauge barely went over 70C.

I was fooled by the amount of air that must have been blasting off the radiator and coming back toward the engine. Putting my hand in front of the radiator was the key as I could feel the air pushing forward. Maybe this is a testament for staying away from pusher fans because they must be far less efficient than pullers.

For those of you who thought this was an airflow problem, you get a gold star! I have a new found appreciation for the "Keep It Simple, Stupid" principle.

Revcor makes three or four different motors which mount to the same blade and guard. I think that with the 16" set up, they range from 1500-1900 CFM. Even the one with the small motor should be adequate. I really wouldn't expect a CoolCat to solve this problem.

Revcor fans can definitely be configured for pusher or puller service. Make sure that the concave side of the blade faces the direction of rotation. If this isn't the case, flip the blade around.

A slipping belt or damaged impeller, or mismatched timing case cover would result in lower water flow rates, which would cause heat to build at higher RPMs. When you slow down after a hot run, heat retained in the head and block can't scrub off fast enough to cool down. (Contrary to what you may read on the web, higher water flow rates are better) This is not an unheard of failure mode.

Removing the pump would also give you the opportunity to restrict the bypass passage. Although I

Thanks for the response Michael.

I finally identified my fan as a 16" puller from Revcor. Getting performance stats on this fan took a few phone calls. I cannot tell if my fan is the regular or high performance model, but both seem to pull less than 2000cfm. The CoolCat would provide a 25% increase in airflow over the Revcor fan with the standard motor.

I also pulled each spark plug the other day to "read" them as advised by my mechanic. Each plug had a very dry, thin, powdery black coating. This is consistent with either slight richness or excessive idling. The good news is that there was no damage to the plugs, evidence of a combusion leak, running lean, or oil fouling. I cleaned the front two, checked the gap and reinstalled them since the mechanic just replaced them last week. I replaced the four rear plugs and gapped them at .025". My mechanic also verified that he did set the timing and adjusted the fuel mixture.

I do have a question regarding the water pump theory. If the water pump was bad and needed to be replaced, wouldn't the car overheat all the time? Even at idle in my garage or on the highway?

A full shroud would be more efficient that an integral shroud, but nevertheless, a 16" flat fan should be sufficient. Many people run set ups just like yours, and report excellent temperature control. I don't see any need to change your fan.

There is no summer version of the Otter switch, AFAIK. The stock Otter switches weren't especially accurate, but I think the design temperature was around 78C.

At this point, my suggestion would be to go back and check your idle mixture and timing. If these are ok, I think you're headed for a new pump.

Thanks for the feedback.

The fan is definitely pulling air through the radiator toward the engine and seems to be fairly powerful. Although this particular fan may not require a full shroud (or cowl), I believe it would be much more efficient with one. If this particular fan isn't designed to work with a full shroud, I may consider switching to the CoolCat. The current fan is only forcing air through 70% of the radiator at best. This may not be the root of my problem, but I think it would help.

I did buy an infared thermometer a couple of months ago and tested the radiator again at idle in my garage just yesterday. The difference in temperature between the inlet and outlet pipes was at least 10-12C, which leads me to believe it is working fine. I let it run for about 15-20 minutes and it never got above 70C. The mechanic installed a summer thermostat. The radiator got hot and the fan came on. I assume there is a summer fan switch too.

Which led me back to my trusty official workshop manual. The factory summer thermostat you mention is supposed to start opening at 70.5 and fully open at 75.5. The factory winter thermostat is 73.9 and 86.1 respectively. The factory fan switch is supposed to come on at approximately 80 and shut off when the temp has fallen to approximately 72. The fan I have is coming on way before 80.

I'll get back shortly with more info.

I just thought of another potential issue that may have an impact on my problem. My car does not have a fan shroud for the radiator.

I also just realized that there are excellent photos of my car online. Just go to xkedata.com and search for my car number 880644. These were photos that the dealer I bought it from took. I just received my heritage certificate and will update the site in a few days.

Anyway, check out the picture of the fan and radiator and let me know what you think.

Edited on 2005-06-24 8:35:58

Patrick - I've heard both stories on aluminum radiators. The mechanic tested the radiator flow before I picked it up. He said it was fine. The radiator is only a couple of years old and has no apparent external damage. I'm using a 15lb radiator cap and it has been replaced with a new one. I have Prestone 50/50 in the radiator with a bottle of Water Wetter. I checked out their website and it is ok to use it with plain water, ethelyne, or glycol-based systems. It does perform best with just water.

I'm sure my temp gauge isn't 100% accurate, but it has been checked vs. a infared thermometer and the sending unit was replaced. The only two times I've overheated is when the gauge hit 110. I'm pretty sure the gauge has either been replaced or refurbished.

Does your car overheat often? I have read stories that say Jaguar owners should expect their cars to periodically overheat and I've read stories that say if your car ever overheats something is definitely broken.

I also checked the lower hose and it does have a metal pipe in the center section as I described above. I guess the guys who rebuilt or restored this car knew about this weak spot and compensated for it. I am planning on calling the previous owner to see if he replaced the water pump and have a few other questions for him. I will also take it on a few short trips near my home to see how it performs.

I have read numerous times that having an aluminum radiator does very little in regards to doing a better job of removing heat over the conventional. Sure hope you don't have a crimped line in it somewhere!
Also, check the instructions on the wetter water; I don't think it's supposed to be used with anti-freeze in the radiator, should just be water with the stuff (I think). As mentioned above, there is now way to tell the actual temp. of the water except with expensive test equipment. The gages on an e-type are highly inaccurate, and there is really nothing you can do about it. The only time I know that I'm over-heating is when the gage pegs or when I'm blowing out water. What rating rad. cap are you using? I guess I'd have the pump reworked as well, but its a PITA (like all water pumps). Good luck and let us know what it was.

Patrick McLoad
1966 E-Type, Right-hand Drive Roadster
#1E1445

Thanks Steve, I will keep Terry's in mind.

I have a follow-up question. What is the "normal" operating temperature of my car anyway? I read something on this site that said a XJ6's normal operating temperature was 88-90 degrees and should never exceed 100 degrees on even the hottest day (unless something is wrong). I assume this means on the road in traffic, etc. This makes sense because 90 is in the center of the temp gauge on this car. However, 70 is in the center of the Series 1. I understand that my climate is hotter than England, but shouldn't the increased efficiency of my aluminum radiator more than compensate for the increase in ambient temperature? This is assuming everything is working correctly of course.

Nick,

If you pull the pump and it needs a rebuild, consider sending it to Terry's Jaguar in Illinois. (NAYYY, just love what they did to my pump). Quick turn-around, and as I recall, they use an improved impeller on the pumps that increases efficiency.

Let us know what you find.

Steve

Thanks for the response Patrick. My car does not have the original fan. It had been replaced with a multi-bladed after-market fan. I'm not sure if it is a CoolCat, but it looks very similar. The header tank and radiator were also recently replaced. The aluminum radiator is top of the line from XK's Unlimited. The fan consistently comes on around 72 degrees and is blowing in the correct direction. I do know that the fan has an impact on the temp when I let the car idle in my garage. It reduces the temp from 72 to about 65.

I agree with your assumption though that there is some type of problem here. Maybe the highway speed was forcing enough air through the radiator and engine compartment to mask the problem until I got off the highway. This leads me back to Steve's suggestion that something is up with the water pump. It seems plausible that the pump was working good enough to keep it at 90 degrees with significant airflow, but not efficient enough to keep it cool at slower speeds. Curiously, I have not found a receipt for a new water pump from the previous owner.

Nick: It has been my experience down here in Texas that on hot days, the slight pitch on the original radiator fan blade does little to pull enough air through the radiator. I assume you are using the original fan motor and blade. I swapped mine out and installed a CoolCat unit. It attaches to the same mount using 4 studs as the original. There are no wires to cut as it uses original wiring connectors. This fan pulls a huge amount of air through your radiator and should solve your problem. You can install it yourself. However, if you show at concours (champ division)and are in the hunt for points, then you'll have to swap back to original fan. Here is their website:

http://coolcatcorp.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=CS

Although timing, hoses, thermostat and other stuff can have an effect, I believe that its fundamentally and ultimately a problem of air movement through the radiator. When you're at speed, there is plenty of air entering the nose and radiator; when you slow to a stop, there is not enough. If you install a CoolCat, all of your cooling problems will go away.
My 2 cents

Patrick McLoad
1966 E-Type, Right-hand Drive Roadster
#1E1445

Thanks for the quick response Steve!

I have heard stories about the lower water hose collapsing and will check that out. I will also verify whether or not the mechanic replaced that hose. I do know that the hose originally on the car when I bought it had a metal pipe in the center. In other words, hose/clamp/pipe/clamp/hose. I'm not sure if this is stock, but I assume this was done to prevent collapse.

The thermostat was replaced by the mechanic. I assume he used the correct one since he specializes in XK's and XKE's, but I will double check. The mechanic also replaced the temp sending unit and verified the gauge accuracy with an infared thermometer. My car definitly overheated due to the amount of coolant that was expelled through the overflow pipe.

The car doesn't pop when I take my foot off the gas, so I wouldn't think the fuel mixture is an issue. I asked the mechanic to check the fuel mixture and adjust it if necessary. I'm pretty sure he did this but will double check.

Your water pump idea is interesting. The mechanic actually brought this up too when I called him back. I would assume that if the previous owner would have gone through all the trouble and cost of rebuilding a Jaguar engine, he would have replaced the water pump too. It seems like such a trivial cost compared to everything else. I will check on this too.

Edited on 2005-06-23 10:22:15

Nick,

I've had some experience with overheating Jaguars, so just a few thoughts. Perhaps some of the real experts can chime in.

I had a similar problem with my old V-12 Jaguar. Turned out, it was the return hose from the radiator to the water pump. The hose was old and soft. It's easy to forget about that hose, down on the bottom there, but what happens is, at highway speeds the suction from the water pump can suck the hose closed, causing a lost of flow through the block. The engine heats up, and then when you slow down and stop, the "heat sink" effect causes the engine to overheat and boil over. Check that hose and if it is old or soft, change it. Old hoses can also delaminate on the inside and cause flap that makes a blockage that you might not otherwise see. (Some car companies actually installed stainless steel springs inside the return hoses to prevent this kind of collapse, but not Jaguar.)

On my '70 FHC when I got it, I had the same sort of problem. So, of course, I checked the hose. Not the problem. I checked everything out and found nothing. Then the water pump started leaking. So I pulled it out to have it rebuilt. Well, to my surprise, the impeller on the pump was a mess, badly corroded and not moving much water. I sent it out, had it rebuilt and a new impeller installed. Put it back in, and no more overheating problem.

A couple of other thoughts. The gauges on these cars are notorious for not being accurate. Check the actual temperatures with an infrared thermometer under the hood.

Have you checked and changed the thermostat? Depending on which temperature thermostat you are running, the "normal" operating termperature will be higher or lower. Also, you MUST have a thermostat that has the by-pass cutoff. Otherwise, too much water recirculates through the water pump without going through the radiator and you will tend to overheat.

Last, even though the cooling system is working right, overheating can be caused by running too lean. Check your carbs and have the exhaust emissions checked to be sure that you are not running really lean. When you take your foot off the gas under load, do you get popping out the exhaust? That is often a symptom of running lean, but best to adjust the carbs and check emissions.

Hope that helps.

Regards,
Steve Weinstein, JTC-NJ
'70 XKE FHC, '69 XKE OTS