I've been interested in streamlining my cooling system since I started researching the car. Disabling the "bootstrap" circuit seemed like a good start, but I've also considered getting the taller V6-style hood, maybe even doing E-type styled louvers, upgrading to electric fans, and of course the electric waterpump.

The thing I worry about is that the electric waterpump will be difficult to diagnose if it starts to go bad, and electric parts make me a little more nervous than mechanical parts on average. The price is also a bit of a disconnect. I've seen one for about seven hundred dollars, conversely a mechanical water pump is substantially cheaper. No way in hell would I skimp on a cheap electric waterpump though.

Post shutdown cooling continues to interest me, so the waterpump has still got its hooks in deep...

 

Do a bit of searching on the forum, someone fairly recently did a thread on it. He posted up a few sensors in the car and recorded the shut down temps.

Interesting that some people found it condemning and some people felt just the opposite. I fall into the latter, it was really only about 20-30 degrees, nothing that would be considered overheating or anything that would be much different than exposure to 20 less degrees for hours on end on the highway or around town.

As far as the thing breaking down, I wouldn't worry too much. You realistically can't look inside a electric without taking it off anymore than you can a mechanical. The only indicator for most people is bearing noise/age/weep hole leaking, which you can pretty much get with an electric pump too.

No idea if the tend to last longer or not

 

Because of a misadventure while installing the GM LT1 v8 in my 83XJ wuzza six, I solved it by using a Meziere (sp) electric pump. It has performed perfectly. No after run feature wired in. I use Efans as well, no after run. The car runs right at spec.


And, should I lose it's serpentine belt, I am not stranded. I can limp a while. No power brakes, power streering or alternator, but cooling is still viable.


I've wondered as to making it temperature sensitive like the e fans.


But, now, I am swamped in a was a no crank to now crank but no start. Relay issue and possibly a blown fuse or worse, a fusible link.


Gonna rob the electric air pump of it's relay. None of my spares seem to fit. I thought I had more of the same Bosch types??? Gonna look in my other bins.


Carl

 

I took my '89 out for a short drive and it was running fine. I shut the car off and returned about 45 minutes later. As soon as I started it it was obvious that a seat had dropped.

So far I have not had a seat drop while I was driving but I'm sure it possible under the right conditions.I hope I never find out. One dropped seat experience is enough for me!

Mark

 

Allow me to pose the thought that it was already overheating without your knowledge and the extra heat after shutoff was too much.

 

That was underhood/coolant temps, not necessarily analogous to head or seat temps.

 

I agree that the temps were from the coolant, ambient, and I think center of the V, but the statement that a maintained XJS with a perfectly functioning cooling system will drop valve seats due to post-shutdown heat soak is pretty preposterous if you ask me. If that were the case I don't think anyone would be in this forum.

While there is some difference in heat transfer, since the fluid is no longer being pumped. The numbers still reflect a common percentage in all parts as far as increased heat. If anyone is suggesting that heat transfer to the valves suddenly changes drastically enough to drop seats, I would like to hear why you believe so.

The valves and the seats are generally being cooled by the air flow around them as the engine operates, and while they stop moving and are allowed to soak some, the engine also ceases to produce heat at precisely the same time. The sizes, metals, tolerances,shapes, every bit of engineering that goes into the engine takes this heat transfer into account, and that is exactly why you cant restart your car again and again.

sorry I just can't get my head behind the thinking that a normally operating jaguar v12 just drops seats at the tip of a hat due to inevitable post shutdown heatsoak. If you can show me the science and all the dropped valve seats, be my guest.

 

All I know for absolute certain, is that I drove this car on a fairly cool moring, about 10-11 miles to a British car club event, stayed about 3 hours, drove home, parked the car in the driveway. Not seemingly running the slightest bit hot. Parked it in the driveway. Stayed at the house for about 3 hours, and was going to a local cruise in. As soon as the car started, I heard it. All I can say, is that it dropped out, while cooling down. This isn't hearsay, its personal experience.

 

OK SS, why do you think the seats loosen and drop down?

i have my own opinion as to why!

 

Only the intake vale is being cooled by the airflow. The exhaust is being heated.

In the case of dropped seats, is it only one type of valve or could it be either?

 

What do you mean? The XJS is notorious for overheating when the cooling system isn't in good condition. They drop valves because they overheat.

I am just saying that post shut down heat soak is way different from the overheating that happens when the cooling system isn't doing its job
I don't know what he means by operating normally either. I have overheated the hell out of my XJS multiple times and the only indication was the needle, it didn't ping or do anything. It is very capable of running extremely hot with no complaints, which is part of the reason they get into so much trouble. People neglect the cooling system and keep driving it because they can, it then breaks something.

I am not saying there is no chance it dropped a valve and wasn't overheating before shut down. I am just saying the car is prone to overheating, which will cause a dropped seat, but the car gets shut down and restarted thousands of times, why would one more post shutdown heat soak cause such a failure?

my mistake, 2 am. You should see the typos I make before I edit some of these posts lol.

They are both being heated, but both are being cooled, its just the intake is getting extra cooling from the fresh air.



Let me be clear that I don't think an electric cooling pump is bad and I don't disagree that preventing post shut down heat soak by setting up a pump and fan wouldn't be beneficial to engine wear/life. I just don't think it is as significant as many claim. Hearing my dad talk about when he worked on e-types, just having the post-shutdown fan caused more trouble killing batteries than it was worth.

 

after shutdown heat soak is not from the water jackets, its from the heated oil temps that rise upward into the cooling jackets, and can start coolant boiling.(hopefully not at an exhaust seat air bubble).

oil temps can be as high as 230/260F and synthetic oil only aggravates things(much higher safe running temps for the mechanicals).

early engines had little probs with seats(unless severly overheated), BUT they also ran much cooler coolant temps, like 165/180F tops.

some may not like this,, HE heads were an afterthought for Jag V12s, they were some of the 1st engines to run 195-205F coolant temps. and the famous FIREBALL chamber.

maybe the plastic tensionor dont like hi-temps and fails the chain, maybe its the OIL thats killing them along with seat probs.

im saying a FULL FLOW OIL cooling system with a front mount core.

and cooler thermostats.

if you have any money left, an after shut down engine an electric coolant pump along
with thermo fans, if that dont make these antique engines last ,nothing will!

 

There's no oil anywhere near the valve seats nor is there oil near the cooling jackets. It's sitting in the sump.

 

simple! the heat from the oil inside the engine rises upward into block and water jackets,

the oil heat is contained inside and cant be cooled for a long period of time, V12s have a lot of very hot oil in the sump.

example; try and drain your oil imediatly after an hour drive!,, tests have shown 230/260F at the drain plug.

 

Here's a guess...

Keep in mind, a temperature differential isn't necessary, but a difference in the coefficient of expansion is.

Aluminum expands as a rate 2 to 3 times that of iron. Thus, the valve seats and heads are always in some sort of competition with each one, one always expanding/contracting faster/slower than the other. One hopes that the engineers took this into account in the design process so that when things are running at "normal" temperatures the conflict is incidental.

But suppose things get too hot??? The aluminum valve seat is expanding into the cast iron head more than expected, and of course the cast iron head is "expanding" (crushing) the aluminum valve seat more than expected. The valve seat isn't going to fail when it's hot...it's going to fail when its cooling...when it and the cast iron head are "retreating" from each other i.e., the aluminum, having lost some of its elasticity from the repeated crushing of the stronger cast iron, no longer fits snugly into its allocated space and *poof*, it gets loose and drops.

I'm more knowledgeable of physics than engineering, and it could be that the above is complete fancy.

Does it make sense?

And if it doesn't, why?

John
1987 XJ-S V12 (with electric water pump and electric fans)

 

The combustion chamber is far hotter than the oil or anything else- the heat is radiated outwards into the coolant and oil, not the other way around irrespective if the engine is running or not.

 

The seat is cast iron, the head is aluminium/aluminum.

I can see the seat losing it's tight fit during an overheat situation for the reasons you've described, but not after shutdown.

 

Huh? How is the oil being heated? The heat all originates at the explosions being harnessed for power and moves out from there. It doesn't originate in the oil and transfer from it. post shut down heat soak has zero to do with oil. It is simply the fact that even though heat is no longer being made it also isn't primarily being transferred via convection but rather mostly conduction. So all of the heat "soaks" into the rest of the engine.

Yes part of the cooling system is not only the convection from the actual coolant, but also the oil (if it has a cooler) but that is not the primary job of the oil nor does it have a considerable impact of the operating temperature.
Also, your point about synthetic oil not helping makes it seem as though synthetic oil is hotter or causes an engine to run hotter because it is capable of doing so.

If you can explain how heat soak is caused by oil I would enjoy hearing the explanation.

I also don't understand why you think it would be good for the engine to run at 165F or where you got that info. That isn't operating temperature and would cause more wear and lower efficiency.

If there is some info stating that the pre-he is less prone to dropped seats, it would most likely be attributed to there being more head to transfer heat to. The valves stay cool by transferring heat into the cylinder head in the split seconds that they make contact with it. The pre-he is probably just better at that transfer. Could e something else, like different metals used or low comp, but that would be my guess. I have never heard that though, so idk

 

exactly.

The expansion is accounted for, which is why you can restart your car everyday. Also why you can't just yank the seats out with a slide hammer.

 

Yep...got my metals mixed up. Head is aluminum, seats are iron.

Principal is the same thought, the expand and contract at different rates.

Thanks,

John