Hey guys, I know there are a ton of threads on overheating, but PLEASE help me talk/think through this.



1989 XJS: new "Cat Cooler" Aluminum radiator, new hoses, new fan clutch, new thermostats with jiggle pins at the top, TEFBA filter, coolant flush, properly functioning electric fan, numerous bleeding sessions to make sure there is no air in the system. So, she doesn't exactly overheat, but I feel like it should run cooler. Sometimes it stays significantly below the N, but then other times it runs up to the middle of the N, and then other times it goes just above the N. What are the other obvious things that I am missing here? I don't get why it doesn't behave the same all the time. I just got an infrared thermometer, so I'm going to check the actual temperature of both banks while its running to see if the gauge is correctly indicating what is going on under the hood. Is there something obvious that I am missing?

 

Maybe the Filter has something to do with it, have you tried it without the mesh to make a comparison.

 

Are you talking about the TEBFA filters? If so I have never had any problems with them and I've hd them on the car for well over 10 years. BTW...painted the filter caps a Ford racing blue color for a little extra color under the hood. Looks good.

 

I did a similar refresh with a Wizard aluminum radiator and my needle seems to sit at the lower end of N and I've seen it nudge to the middle every so often. I'm assuming it's just the thermostats doing their thing.

One obvious (and fairly painless) thing to check would be to confirm that the the centrifugal advance isn't stuck. (Lucas Ignition (to 1989)).

Jim

 

I have a Marelli car, so I think that rules out the centrifugal advance issue. And I hadn't thought about trying to run it without the TEBFA mesh in place, but its worth a shot I suppose!

Any other ideas?

 

The movement on the needle you describe will be only about a 3 or 4 degree change in the temp that the sensor is seeing, and is entirely normal. Absolutely nothing to worry about at all. Where the needle sits is pretty arbitrary, if you changed the sensor it is damn near certain the normal needle position would change. It is a good idea to take the temps externally, but hard to get an accurate reading.
It is just remotely possible your water pump has a slightly pitted impeller, but I doubt it. If you are really worried, plumb in an accurate digital temp sensor to the gauge sensor port and see what it says.

 

+1 with Greg.

Mine had the hissy fits way back, and eventually found the radiator header tank pressure cap, NEW, was blowing off at an erratic 4lb, instead of the 13lb stamped on it.

Ratted around at work, and with my pressure tester, found a cap that actually blew off at the 13lb I wanted, duly fitted, nothing else done, problem solved.

You might be so lucky also.

 

What are the 'sometimes' conditions when this happens?

If you mean that this fluctuation occurs randomly as you drive along then it merits investigation.

If you mean the temp reading fluctuates in accordance to different conditions, there might not be anything wrong at all. For example, if it stays at the bottom of the "N" as you gently motor along on a cool-ish day but goes to the top of the "N" if stuck in gridlock traffic on a hot day...I wouldn't worry, personally....as long as it doesn't keep going up-up-up with no end in sight!



One possibility is there is absolutely nothing wrong.

What is your expectation here?



Judging by my own experiences, if the fluctuations are occurring randomly, my bet is that you still have air in the system.



Good idea on the infrared thermometer so you can get a rough idea of actual temperature. On my old XJS the bottom, middle, and top of the "N" corresponded to about 180º, 190º, and 200ºF.....all of which are perfectly safe temperatures. Others have reported significantly different results because the old barrel gauges can be flaky.

Owners of the Series III XJ sedan have a slight advantage in that the temp gauge has some numeric markings, with 90ºC dead center....and un-numbered hash marks that could mean anything. But, anyway, mine will sit happily a needle's width below 90 under most conditions. During a recent heat wave, though, I was seeing a reading 2-3 needle-widths above 90 (I'm guessing 95-100ºC) while idling in heavy traffic, going up long grades, etc. I wasn't worried, personally.

All of this sort of explains why Jaguar eventually threw in the towel and joined the ranks of others by installing heavily dampened gauges and/ or dummy gauges, that don't respond to minor temp changes, or respond verrrry slowly.


Cheers
DD

 

With your coolant flush did you use any heavy-duty cleaners? A new radiator is nice but whos to say the bowels of the engine arn't clogged with sediment? I've flushed my car at least 6 times now with a semi-truck grade spin on filter installed and it still pulls silt (or stopleak thats been ground to sand??) and this has gone on for the past year.

 

Please note that in traffic, the engine running temperature is mainly determined by the switching point of the fan switch, not the thermostats. On my XJS I fitted a lower temp switch for this reason, from a SAAB.

 

So, about a week ago, I took it for a drive on the interstate and the gauge stayed about half a cm below the N. It stayed like this for over an hour. Then, I took it out the next day and it went up to the edge of the N and then slightly over, regardless of moving or not. I guess I was under the misguided impression that it should pretty much stay in the same spot all the time like a modern car.

 

Another weird thing: last night I finally completed my Vee cleanup while replacing the plugs, wires, and dizzy cap. What a chore that was... but anyway after I started it up, it ran nicely and I let it get up to temperature. Then the cooling fan began cycling on and off. Never in my ownership has the fan turned back off after turning on, so the cycling was pretty exciting because it said to me that the car is actually properly maintaining it's temp. So, is there any reason that the car would run cooler or maintain its temperature better with new plugs, wires, and dizzy cap? I feel like the answer to that is no, but it was really weird to me that the fan started cycling on and off properly...

 

My situation is a bit similar to yours. Did what seemed sensible to ensure good cooling-new rad, thermos, hoses, main fan (fan clutch passes the standard tests so have kept it), coolant flushed and replaced properly (one hopes) by professionals who work on Bentleys and Lamborghinis and the like (not your local Pit Boys equivalent, in other words), and she still edges over the middle mark when idling at the lights (post-facelift car). On a hot day she can go as much as a needle-width gap past the middle marker when stopped in traffic. But she always drops back down when moving off.

I have, however, with assurances from people like Greg, Grant, and Doug (the Holy Trinity), accepted that this is in fact normal. I admit, it's hard to read all the warnings about Never Ever Ever Oh My God No Never Overheat the Car and then read about people driving through Death Valley in midsummer with their engine temps apparently low enough to keep their beer frosty, and panic that a millimetre or two above dead centre means your engine is about to implode, but... it doesn't.

On the early facelift cars like mine, there's a broad area marked out with three white markers at the bottom, middle, and top end, and that's the safe area. Mine's never gone beyond that. On the later facelifts, presumably to deal with heating panic issues like I suffer from, they eliminated the markings altogether in favour of a single white zone, so there's literally no mark the driver might panic once the needle passes (at least within said white zone). I kinda wish I had that and the idiot needle....

I didn't get a laser thermometer, but I did get thermal sensor stickers and attach them to the hottest parts of the engine to give a record of the peak temps it reaches. Even when the cooling system wasn't working properly and temps were more than halfway to the hot edge of the normal zone, they showed that the actual temps were still acceptable.

Still, that doesn't mean I don't keep a very close eye indeed on temperatures, especially when in traffic. At the moment, she's getting repaired as the rear starboard connector to the water rail is leaking, spilling coolant on the engine (as an aside, it's always hilarious when clouds of smoke pour out of your bonnet), but even then, the temps were fine.

 

I can't think of a good reason.

The fan thing might be a fiddle factor....a loose connection jostled while doing other work or some such.

Cheers
DD

 

"Overheat" means different things to different people.

To some you're not overheating until/unless the needle is pegged and coolant is boiling out and falling on the ground. For others, anything above thermostat rating is overheating.

My owners manual says 'normal' operating temperature for the V12 is 88ºC-125ºC. Now, although I'm nonchalant compared to many others, 125ºC is something I hope to never see. Even my somewhat broad comfort zone has limits. I think I'd get concerned at 105 and pull over at 100. That's just me. There's no magic to those numbers.

To repeat my philosophy, I think coolant *flow* to all areas of the engine is more important than temperature. If you're confident that flow is good I wouldn't worry if the temp needle ticks up a bit under some situations. I don't believe that indicates a fault to be corrected.

When you run a Jag V12 you have to worry about the cooling system. Knowing how much worry is just right, and how much is too much, is the question. Many have fretted, to the point of obsession, over keeping the needle 'at the center of the N' 24/7/365 and, IMO, have often spent tons of money (not to mention tons of effort) needlessly. The level of worry actually takes away the enjoyment of the car.

Just my 2-cents.

Cheers
DD

 

I agree very much about the level of worry affecting enjoyment of the car. I don't want to be one of those who gets obsessed with keeping it dead centre every second either. That said, if the car's specs says X to Y is normal operating range, I have to assume anything up to Y will not actually cause damage. Need looking at, oh yes, quite likely. But not fatal, which is my main worry, at least.

How one ensures every part of the engine is actually getting coolant flow, though, I am not sure about. Pity the hoses aren't transparent.....

I wonder how easy it would be to add in a device to directly read temps and send them to the cabin. Could be interesting to compare how much the needle moves with how much the actual temps change.

 

We can only ensure that the system is very clean and properly bled....and from that presume the flow is good.

The "Lutz mod" improves coolant flow. I've considered giving it a try but never felt any overwhelming need

Cheers
DD

 

Anyone who is truly worried should buy a two probe remote temp sensor such as this
6802 II Dual Channel Digital Thermometer with 2 K-Type Thermocouple Sensor Probe | eBay
and tape the probes to thermostat housing exit to the rad and from the water pump intake casting. Then run the wires to the cabin though the doorframe rubber seals and take temps on the on the move from the cabin. Assuming the cooling system has been properly serviced, I am prepared to bet that the top hose rad intake temp is never above 100 C and the rad intake temp never above 90 C, even in the most extreme conditions; while usually they will be much lower. Of course real V12 aficionados can install permanent temp sensors in both thermostat outlets and one in the water pump intake, with a switchable digital interface in the cabin that reads them as selected! But the temp probe will reassure you more cheaply and with no bother.


Re the Lutz mod, which I have done and believe in, here are my thoughts and findings:

1. The theory: The exit holes from the heads to the water manifolds (and thus to the thermostat housing and the radiator) are all the same size front and back of the head. Therefore there is a tendency for water closest to the pump to short-circuit the engine, and preferentially flow out of the front part of the engine exiting through the front part of the heads. Thus, the theory goes, the rear of the engine sees less effective coolant flow and so runs hotter than the front.
2. In racing conditions this is undoubtedly true, and all V12 racing teams paid great attention to getting water flow though to the back of the engine.
3. The theory is ALSO true in normal road engines, I believe. However, the question is: does it matter? Well I did about 100,000 miles in my car BEFORE I did the mod, with absolutely NO problems at all. So have thousands of other V12 owners; so in the real world it probably does not. However, it seems a very good idea to promote even cooling across the length of the engine, so that is why I did the mod!
4. The Mod (as invented by Norman Lutz the famous Australian engine builder, who is also helping our own Warrjon with his engine): consists of reducing the diameter of the holes allowing water to exit the head into the FRONT water manifold and thus back to the radiator. In this way pump pressure forces more water into the back of the engine, thus equalising the actual flow volume between the rear and the front water manifolds. (see attached pics of the modified front water manifolds, clearly showing the original and modified hole diameters. Norman Lutz gave the required diameters to equalise flow).
5. Gauge temps: I "proved" to my own satisfaction that water flow WAS preferentially short circuiting the engine on my car (even if, see 3 above, it may not/does not matter!) because as soon as I did the mod, the gauge temp showed a bit hotter, and the needle immediately sat almost on the N rather than below it. You would expect this, as cooler water is being forced further back rather than going straight into the front water manifold where the gauge sensor is. So one effect of the Lutz mod to improve cooling is to make the gauge run higher! Of course, were the sensor at the rear water manifold, it would show cooler!
6. Having said all that, someone on the forum, and I have forgotten who to my shame, actually did install proper gauges in both back and front water manifolds, with no Lutz mod, and found the water temps within a degree or two the same!

Greg

 

I am properly Paranoid about my Car overheating, so every time before I go out I always Top up the Coolant in the Rad and in the Header Tank,

till they are overflowing.

So far so good but I always carry a couple of gallons of Coolant just in case.

But that's just me.

 

Interesting. This certainly reinforces the idea that the needle moves quite noticeably with just a few degrees of temperature change....