I got my first data collection from the temp sensors I put into each water manifold. This was as much a test of the data collection method as anything else since there is still to much snow on the ground for me to take the cat out. So this data is at idle, although I did rev it to 3K for a minute or two.

When weather permits, I take it out on the road and do the same thing.

My car has two electric fans, but the current setup has one fan always on when the engine is turning, and the other controlled by the thermal switch, so it's similar, but may not mimic exactly, what a car with an engine driven fan might do.

Cheers,

John
1987 XJ-S V12
63,000 miles

 

JCR
This is really interesting. There is so much unmeasured hearsay about the respective temps of each bank, and between the ends of each, that a proper measurement and definite data are well overdue. Congratulations for getting it done.

I am looking forward to your results once you give the car a decent hot run, as well as when outdoor temps are higher, later in the year. Thanks for sharing this stuff

Greg

 

Thanks Greg. I'm trying to compile the same sort of thing under different conditions...thermal fan only on...bonnet immediately opened after shutdown...both fans running after shutdown...and so on.

Of course the real fun will come in mid summer!

Thanks,

John
1987 XJ-S V12
63,000 miles

 

Did an actual drive yesterday (for the one day streets weren't covered in snow...got more snow today, so she stays in the garage for a bit). Graph is attached.

Observations...

1. In both this test and the earlier one I posted, the left bank runs cooler than the right bank by about 10 degrees F, which is contrary to what Kirby expects on page 173 of his book. Well, maybe :-). It's cold here, and it could be that the thermostats never fully opened, or maybe didn't say fully open for long. I'm not an engineer, and I don't have an explanation for these results. More testing, especially when it gets hot here, will maybe yield different results.

2. There seems to be not much of a difference between the front and rear temperatures overall. At extremes it runs around 5 degrees, but for the most part the fronts and rears are within a couple of degrees of each other.

3. Unmistakable, and expected, is the quick temperature rise after shutdown. Six to seven minutes seems to be where the temperature reaches its peak in the two tests I've done so far. I'm thinking that the next test will be to run both fans for 15 minutes after shutdown and see if that keeps things cooler.

Thanks,

John
1987 XJ-S V12
63,000 miles

 

Really interesting, John. The post shutdown figures are, I believe, one of the most important aspects of preserving the V12 in an XJS body. I have always popped the bonnet when I stop the car in even warm weather. I will be very interested in your bonnet open tests when the time comes.

Also, when the ambient gets to 80°, whether the running temps chnage much.

greg

 

I've never really thought about it much before but I have always seen a lot of emphasis and worry about the rising temps after shutdown.

I'm sort of thinking aloud so anyone please tell me if I am mixing something up, but it seems like it really isn't a big deal. I mean it sucks if you immediately restart the car because the cooling system has to do some extra work....but otherwise does it really matter?

So the highest temperature is in/near the combustion chamber and the coolest spots are furthest away or items that are being cooled. As soon as the engine shuts down the water pump is no longer circulating, so the coolant can no longer carry that heat away. This means the heat creeps through the rest of the engine and engine bay, heat that usually stays in one place, so the whole engine is "hotter" if you will. The coolant in the engine is no longer moving and absorbs more of the heat than it normally would, and results in a higher temperature reading in the coolant.

So there is this idea that the engine is now "overheating" in a way because the temp reading is so much higher than would be considered "normal". But the engine is NOT producing heat, it is only cooling, which involves the heat spreading to cooler areas.

Doesn't that just mean the idea that the engine is "hotter" is only because it is hotter overall? EG area 1 is 1500 degrees and area 2 is 160 degrees. Now are 2 is 210 degrees so it SEEMS like the engine is hotter, but area 1 is no longer 1500 degrees because it was transferred to area 2.

if the temps here were read on the cylinder walls or valves instead of in coolant passages wouldn't they read LOWER over time rather than having a spike that is so worrying to everyone?

 

My take has been that the this issue isn't really overall engine temperture or even coolant temperature, per se.

Rather, it's the worry that isolated areas will superheat and steam pockets will occur.....specifically in the cooling passages near the valves. Steam can't absorb the heat like liquid can....so the area near the valve seats overheats. And that's where the problems start.

This is the worry with the V12 with or without the engine running.

With the engine running we avoid a problem by ensuring good coolant *flow* . Clean radiator, clean passages, properly bled system.

With the engine off we hope that post shut-down e-fan operation will do the trick....and/or open the hood to help ventilate the heat.

<shrug>

Cheers
DD

 

Many modern cooling systems now have an auxiliary electric cooling pump. Would one of those benefit? It could come on with the fan. Where should it connect if it were to be used? There is no common place to suck from is there but any thing that pushed fluid in to the cooling side at the bottom of the radiator would help, yes?

 

There shouldn't be any steam though, it is created when the coolant boils. After shutdown the system is still under pressure, plus the right amount of antifreeze brings the boiling point way up as well.

If the heat increased significantly after shutdown it would blow the radiator cap and steam would be released there anyway

 

I'm thinking an electric cooling pump is probably "the answer". I'm trying various things with the fans, but I can't say I have much hope of them making a difference...all in all there isn't much point in running fans to cool the coolant in the radiator if there is no circulation of the coolant into the block. However, there may be some merit in running the fan(s) to get air across the top of the engine, which one would think would reduce the baking time of the wiring.

Over the weekend I did a re-calibration of all the sensors, hoping to try and understand why my results (my left bank always running cooler than my right bank) should vary from what Palm expects. I did find a calibration fault in the rear sensors, so I do now see the rears running hotter than the fronts by about 10 degrees F, but no explanation for the left-right issue.

I'm running another test as we speak, all with the bonnet down through the entire procedure. Sadly this is another "idle" test, as ONCE AGAIN, the snow is falling pretty heavily :-(

Doug could be right, it may be more of a steam pocket issue than anything else. I just have no way to measure that sort of thing, so I measure what I can.

Cheers,

John
1987 XJ-S V12
63,000 miles

 

unless there is air trapped in your system there is zero possibility of a steam pocket

either way the engine being an additional 30 degrees for 30 minutes doesn't compare to it being running temperature for 8 hours ( think roadtrip)
Engine bays live in a lot of heat and all of the components within it are stressed by them. While it is helpful to relocate the harness from the V nothing else you can do it going to vastly improve the life of any part in the engine bay by reducing 20-30 minutes of an additional 30 degrees. If it weren't much of an effort then why not.....but it sounds like you are going through a lot of effort to come up with a solution to this "problem". All cars do this, it isn't a big deal.

If you want to improve the life of the engine work on the actual cooling system to reliably bring down running temps (which expose the engine to heat for much longer periods) or find something else important to do that isn't often done, like changing your brake fluid or replacing the hoses on your fuel injectors.
Obviously you can do whatever you want, it just rattles my brain to think there is someone somewhere struggling to solve a problem that doesn't need that kind of attention

 

A lot of good points here. I'd have to think that some hot shutdowns would be a lot worse than others, for example coming right off a high speed highway run vs a leisurely city cruise.

My only real evidence on this is from my past driving a big truck, don't know if it applies directly but the main concern with a hot shutdown on that was the turbo - shutting it down hot would cook the oil in the turbo bearings which would cause it to fail a lot sooner. My truck had a pyrometer - a gauge on the dash that showed the exhaust temp. It was pretty amazing how hot it could get - the worst was pulling up hills, but highway temp was also a lot hotter than low speed. Idle temp was very low. I always tried to let it idle for a couple minutes before I shut down.

A lot of this may not translate directly - big diesel vs gas, turbo vs non and the turbo was cooled only by the oil flowing through it - but I'd have to think the basic concept is sound ie the combustion chamber gets a lot hotter when run hard. If it gets hot enough to damage anything in the Jag I don't really know. I think your idea that it will continue to cool is correct, but but it will cool faster and more evenly if the coolant is still moving. I would tend to believe that problems would arise more from from a big temp contrast when shut down since the engine can obviously handle the temps when the cooling system and oil is in motion. I normally try to let it idle for a minute or two before shutting it down.

 

I pretty much agree with you here - I don't think there is enough of a problem to warrant a special after driving cooling system. I do think it's worthwhile to let it idle for a couple minutes after coming off the highway or hammering up a mountain before shutting it down. And to keep your cooling system in good shape of course.

 

oh yeah everyone should agree there, any serious driving should be followed up by 20 minutes or so of leisurely driving to let the system cool down gently. Most owners manuals of most manufacturers state this

 

I agree that once the engine is shut off it's not producing heat, but it's also not being cooled anymore, (other than through radiation and a bit of convection through the cooling system) since the coolant flow has been shut off. So the steady "flow" of waste heat from the cylinders to the atmosphere via the radiator has been stifled. Thus the temperature rise of the coolant and the engine internals made of aluminum and iron, two metals with significantly different thermal expansion coefficients.

And remember, this is on a 27 year old engine! Maybe it only is 30 degrees hotter for an hour a day (two trips a day = two cooling periods) but over the life of the engine that amounts to nearly three YEARS of it being 30 or so degrees hotter than it really needs to be after shutdown...and heat above any beyond operating temperature is never a good thing.

Did Jaguar (or anyone else for that matter) design this engine to go through those temperature cycles for 27 years...I doubt it. After all, that's no way to sell cars!

I have a vested interest in keeping this thing running for as long as I can, and I'm talking about 10 to 15 more years. A warped block or dropped valve seat will end that plan, and assuming that it only would need a rebuild I don't know that I'd be able to throw $10K into it all at once, assuming I could find anyone to even do it.

So...at worst...reducing or eliminating the excess heat after shut down won't hurt anything. If that ends up involving an electric water pump, that will also help keep the engine cooler while it's running, especially while sitting in traffic or just creeping along, since unlike the engine driven pump (which is pumping its slowest at idle) an electric pump can vary its speed according to cooling demand. But I digress...

In the end we'll never really know if what I'm doing "helps" or not...only time will tell. But I enjoy doing it, I'm learning a lot about the engine in the process, and I do tend to like overkill. To me this is much more than a car, it's a laboratory on wheels. So, I'll continue to share what data I can and folks can do what they like to with it as they desire.

I've attached a list of some of the things I've done to it, if someone sees me missing something obvious (next project is the fuel tank and such) let me know.

Thanks,

John
1987 XJ-S V12
63,000 miles

 

Like you I wish to preserve my XJS indefinitely. That is a great list of mods you have posted. I have done almost exactly what you have on the fan system. Otherwise the biggest cooling mod I have done is this:


There is no question about it, the real problem with cooling the V12 XJS is the air path through the radiator stack. Once this is improved (and it is very easy to test, just unbolt the front bumper and go for a spin in hot weather) the temperatures drop astonishingly.

As you mentioned, on my car the 'fan on' LED I have fitted glows brightly now when the fan is NOT powered, indicating the fan is windmilling very fast, whereas before the mod it never glowed at all. All cooling stuff was brand new and completely clean after my rebuild.

I did this mod soon after my rebuild because in hot weather after a hot stop, at lights for example, it took far too long once back at road speeds for the fan to cut out and temps to reduce. Now, after a hot stop the fan comes on, but within a mile it goes off as the coolant temperature plunges. I have not measured it, but the underbonnet temps are much lower when I pop the bonnet after a run - things I could not touch before I can now. In addition I have removed the rad surrounding foams. This has had no effect at all on coolant efficiency, but has reduced the under bonnet temps I am sure. the great XJS prophet Grant Francis to thank for this last tip.

Greg

 

The engine being 30 degrees warmer after shutdown is not going to drop a valve or warp a block.

It makes more sense to say your goal is to bring down idle temps....but why are you idle temps high? If they are high, fix the cooling system. If they aren't high...why would you want to bring them down too low? The coolant being pumped is just fine at idle. The amount the coolant is cooled differs, fans are necessary at low speeds and they basically do nothing after 45mph, that's why we use electric fans and viscous clutches

If you want an unnecessary mod to lengthen engine life then go get a blanket heater so then engine is never cold at startup.

want to do more?? Plug the air injection system back in. Why did you remove it?? It allows the catalytic converters to work properly. The cats are heavily involved in the engine management and air/fuel mixture. A mixture too lean or too rich will cause wear to the engine.

 

Why would I want to put the air injection system back in??? It doesn't make anything work properly, it just gets the cats up to temp sooner...and dumps its product overboard after the engine is up to temperature. But since the air pump runs 100% of the time, the pump is always a drag on the engine, even though it may only be needs a few minutes each start-stop cycle.

Anyway, I ditched the engine driven water pump and installed an electric one. More efficient (runs only when needed), takes less power to run that the engine driven pump, and keeps the engine cool after shutdown, which was my goal, not to lower idle temperature.

Oh, for those that are interested, running the electric fan(s) after shutdown is a complete waste of effort. I know Palm et. al. spend some time talking about it, but regardless how long I let them run (and this is two big electric fans, not the stock fan) it had no effect on coolant temps. If you don't believe after shutdown heating is an issue then it's a moot point of course, but if you do then running fans only...at least in my case...made no difference at all.

Thanks,

John
1987 XJ-S V12
64,000 miles

 

John, this is very interesting indeed. I have no doubt that circulating the water after shutdown is a great thing to do as far as maintaining even engine temps are concerned. Where did you put the pump and how have you controlled it?

One question, please: what do you mean by 'only runs when needed'? Is it not running all the time the engine is running? The standard system (I believe) circulates the water though the heads via the cross pipe (but not the rad) even when cold.

REALLY interesting, John. At last you have provided us all with definite data rather than speculation. On my system I have a timer which, if the fans are on when the engine is switched off, keeps them running a minute or two. It also has the effect of protecting the fan relay from burning out from too much on/off switching in traffic for example, as the thermo switch clicks in and out too much under these conditions. So now I know that keeping the fans running does nothing for post shutdown engine temps!

Second question: does post shutdown fan running help with under-bonnet temps though? As these are pretty important as far as protecting wiring life, in my view.

Thanks again for your information and congrats on the way you have gone about getting it!

Greg

 

The pump is in the LH fender well, where the fuel vapor system would be if I could have ever gotten it to work. One day I'll revisit that as I hate the "drill a hole in the gas cap" solution, but that's what I've done. Anyway...

I've attached some photos. I had some copper elbows soldered into the lower radiator connection which direct water into the pump inlet (oh, the white pipe you see is part of the cold air inlet system). The pump attaches to the lower radiator piping, then pumps coolant back through a hole higher in the wheel well, where it goes via a 45-degree copper fitting and a radiator hose to a "blank out plate" (made in just a few hours with a Dremel tool) that fits where the mechanical water pump use to be.

Credit for this goes to Ian Hissey of Australia, who's page I came across while searching about for an electric pump solution...

XJ-SC Modifications

I used the same brand pump that he did, but with slightly larger capacity.

The way it works is pretty simple. There is a temp sensor in the RH radiator inlet (I choose that location since mine runs hotter on the right bank). It reports temperature to the controller. The controller tells the pump whether to "pulse", i.e. pump coolant 10 out of every 30 seconds, run continuously, or to run continuously AND turn the electric fans on. This seems to me an elegant and efficient way to do things.

The system will run the pump/fan combination as necessary up to 2 minutes after engine shutdown. At first I was skeptical if this would be long enough, but it seems to be. In fact I'm really surprised that it works as well as it does. I'll reserve judgement on that as our hottest months are not yet here, but I've had it installed for about a month and have yet to see the coolant temps climb even 5 degrees after shutdown!

I've not yet looked at under-the-bonnet temps, but plan on doing so in the near future. My results may not be representative, as I've pitched the stock A/C compressor and have mounted a Sanden unit where the air pump was, so there is more airflow in the V (I also drilled a huge hole in the throttle pedestal...how much it helps I don't know, but it can't hurt).

Oh..in my setup (and the one Ian uses) the cross-pipe and thermostats go completely away.