Hi All,
I am in the process of swapping engines in my '89 XJS convert. About ready to
drop the "new" engine in. After reading Kirby's book, it seems the oil cooler is kind of inefficient. I noticed the large line that is in my car that attaches to the oil pan is shot. Needs replaced. Is this cooler really necessary?? Would like your
thoughts, as if I can do without the cooler and save room and hassle, I will.
Otherwise I will need to figure out a source for the line, or have one made.
Thanks everyone!!

 

These cars run hot. Hot oil is thin oil and very hot oil breaks down. I think its necessary.

 

Right.

I can't remember the details but two versions of the oil cooler were used. The USA cars, and perhaps some other markets as well, got the oil cooling system that only cooled half the oil half the time.....or something like that. Other markets got the 'full cooling' oil cooler arrangement.

Unless the car was subjected to heavy use I'd be tempted to discard the entire system OR convert it to the full cooling type. The 'half cooling' system....or whatever it is....hardly seems worth the trouble

Cheers
DD

 

Yeah, no.

The designed operating (coolant) temp is 185º-200ºF just like virtually every other car out there in the world.

If the cooling system is working properly then the 12 quarts of engine oil really isn't at much risk of breaking down from heat.

If the cooling system isn't working properly then a V12 owner has much more urgent problems to contend with than oil temperature

Cheers
DD

 

yeah, yes. Anyone who's ever had a car with an oil temp gauge and coolant temp gauge knows they run at very different temperatures depending on many factors even on the street. For example on the track its common to see coolant temps in the low 200's and oil temps in the 300's for extended periods of time. Coolant and oil primarily come in contact with totally different engine components and their temperature relationship is not linear. 1/2 cooled oil is better than no cooled oil. It's typical on may engines including race engines to have about 1/2 of the oil flow through the cooler for safety with a bypass valve. If the cooler ever became dented by road debris and restricted then engine would still have plenty of oil flow to survive.

 

I say absolutely essential ! Oil takes a huge amount of heat out of the engine and without that the coolant is under even more load. If you take the old hoses to a hydraulic hose repair place they will redo them for about 20 quid. Which is about a 200 quid saving on the jaguar price!

greg

 

Yes, we know

What does that have to do with your assertion of "these cars run hot" ?



Yes, we know.




Yes, we know



Yes, yes, yes. Thanks for general discussion about oil coolers, with emphasis on track use.

Let me put it this way...

Is there something about the V12 Jag ("these cars", in your words) that makes an oil cooler particularly important versus other types cars? Does the oil typically get hotter on a V12 Jag than most other cars?

Cheers
DD

 

Absolutely great as an optional thing, I say .

Heck, even Jaguar didn't think it was very important, as they intentionally reduced the function of the oil cooler on tens of thousands of the V12s.


Cheers
DD

 

My opinion is, that the only places these oil coolers really are required are either on German autobahns when exceeding 125 mph (nearly every car has one here) or on a race track. Under normal load and purpose use (long distance cruise) they are neglectable...

 

Yes, I believe so


Large engine + tight space = needs all the cooling help it can get.


The Jag V12 suffers from marginal cooling as designed and it had a oil cooler as designed for a reason.


Older designed engines tend to have more hot combustion gasses get past the rings and into the crank case which heats the oil. The large PCV system on the jag v12 suggests this is the case.


The oil pump on the Jag V12 is a racing design and superior in every way except efficiency. That inherent inefficiency shows up as drag and heat transferred to the oil.


The oil pan is flat and doesn't hang down in the air stream so little convective cooling occurs.

 

I do not entirely agree. What you say about 125MPH runs is true, but not the whole truth, I believe. At a steady 85 MPH (about the continental Europe 'you will not get stopped' speed) on a day when the sun temperature is well over 100°F, and you are driving (say) 200 miles, then the entire engine and gearbox assembly gets VERY hot throughout. Mine takes ages to cool so you can touch it after such a run, and I always open the bonnet under these conditions when I stop.

Without the oil cooler, the heat it would have removed either has to be removed somehow else, or else the system runs hotter still. One or the other. I believe that this would place an extra load on the water cooling system, which IS marginal in these circumstances, even if everything is in A1 shape.

As regular readers may recall; I believe I have proved that the marginality is a function of airflow through the rad stack, not the actual capacity of the system, given adequate airflow.. After my rebuild I thought the car was taking too long to cool down after a hot stop, and a restart to cruising speeds. I had the identical system that I had in the UK, but it is hotter here. The electric main fan stayed on far too long when, had airflow been adequate, it should have stopped; and the gauge stayed higher for longer. The car was NOT overheating mind, just that the coolant temp was not responding to the increased airflow as it should have.

As a test I unbolted the front bumper: 'voilà' as they say round here, as soon as the car got up to speed after a hot stop such as traffic lights, down came the temps VERY fast indeed. My solution has been to do the following (Lucas car): i) move the secondary coil out of the airflow to the side; ii) move the horns out of the airflow to each side; iii) move the number plate to one side of the bumper and cut an oblong hole in the bumper centre (about 12 inches by 4 inches, covered in go faster stainless mesh). You hardly notice it now it is dirty and the cooling is utterly transformed. I calculated this gave the rad stack an extra 60 square inches of uninterrupted direct clean airflow.

So I take away from all this that on a standard car the cooling needs every bit of help it can get, and the oil cooler is a very big contributor. I recall that tests show about 40% of the engine heat gets dealt with by the oil circulating, but I cannot recall the source, maybe Roger Bywater's book?

And I have fitted an extra transmission cooler too!

Greg

 

I'm considering the additional tranny oil cooler, as I know from other cars (mainly Volvos) that a combined water/ATF cooler is prone to damage and is less effective.

My problem here in D is, that I can't modify the front end, without losing my "Historic Car" plate status (will have it in 5 years). So I'm left with accepting the water and oil system as it is... It worked 25 years to date, so why not another 25?

 

Greg and ICS, I'm not convinced that the V12 Jag *requires* an oil cooler more urgently than other cars. However, if/when framed as a 'can't hurt and can only help type' of thing, I certainly agree.

Personallly, I stand by my original thoughts of either converting the system to the full-cooling system or dumping it. The, system, as designed and installed in the car in question, really does very little. I'll try to look up the particulars....probably in Kirby's book....but it's virtually like having no cooler at all.

Cheers
DD

 

Doug
As you say, on my car and all V12s prior to the full flow cooling - the change was about 1988 I think - it is true that only the 'excess' oil from the pump goes through the cooler. I believe this means that whatever the pump delivers that does not go through the engine goes through the cooler. So as you say, it does depend upon what the 'excess' volume is compared with the total. I got to thinking and I have consulted a booklet I have, written by Walter Hassan the engine's designer, about the engine's development. On pages 47 and 48 he has graphs and text about the oil pump delivery to engine and cooler. He says that approx 50% of the total pump flow goes through the relief flow system and the cooler. We are talking total flow her at (eg) 4000 rpm of 20 gallons per minute of which about 60% is excess relief flow and 40% goes through the engine. At lower rpm (eg 2000) total flow is about 7.5 GPM again split 50/50.

The pump is hugely over specced and produces loads of excess volume (essentially by luck) because it was a Borg Warner auto gearbox pump that was used. This being because Jaguar needed the 'thinnest' available and there was a real packaging problem with a standard oil pump's gear drive etc etc. While the autobox pump used sits round the crank and takes up almost no space and needs no geardrive. Basically, by luck, the characteristics of the oil pump are that the faster you go the higher the volume of oil that goes through the cooler.

Greg

 

you could take a leaf out of the TWR race car programme - they had the bonnets jacked slightly open at the back edge, I think, and this allows the air to escape thus increasing flow and cooling.
I think the rear bonnet/hood sealing rubber could be removed to allow the bonnet to be shut, but leaving a wide small gap for exiting hot engine bay air. or cut small lengths of the rubber off and put them back on as spacers to stop the rear edge 'flapping'

 

The only problem with that of course is if you get a hose blow as water/steam/smoke or oil will instantly coat the windscreen and you will be coasting blind.
Should be entertaining if nothing else!

 

Allan Scott's book about the TWR racing XJSs (Christmas present, read by mid day Boxing day, re-read by New Year's Day) is very informative about this aspect. In racing circumstances admittedly, they found out that airflow through the engine bay was extremely poor, to the extent that it created substantial lift, and also contributed substantially to the oil cooling problems they had in racing conditions. As you mention, they rigged up some 'safety pegs' thus allowed by the ETCC regs, that in fact allowed the bonnet to rise about 2 inches and thus help the under bonnet airflow, lift and oil temp problems they faced. Even so, the air pressure differential in these circumstances was such that on one occasion one of the pins ripped out of its fasteners!

Incidentally, in some of the photos of the racing XJSs it is seems clear that the number plate slot has been cut out of the bumper to allow more airflow direct to the rad stack.

I would love to have some sort of grille or slot at the back of the bonnet to let out hot air, but I have not got either the skills to do it, or the resources to get it done well. But removing the rubber, or cutting out a bit of it, sounds a great idea, which I shall try out. Thanks.

Greg

 

Greg,
I bought my X300 18 months ago, and after a while I thought it had poor panel fit around the bonnet/hood. I didnt recall it being like that when I bought it.
Then I realised the 2 'pegs' that hold the bonnet closed are adjustable with a large pressed steel 'lock nut' and it wasnt tight. It was gradually undoing, allowing the bonnet to rise and creating a panel gap. I adjusted it flush and locked up the big nut tight, and it hasnt shifted in the past year.
I dont know if the XJS is the same or not, but if so, the locking pegs could be adjusted so the bonnet sits up a cm or so giving a gap..you'd probably get a lot of helpful comments along the lines of 'your bonnet's open mate', etc. Just tell them it's for racing!

 

I will tell you from experience to convert a passive oil cooler engine to a full flow system is a lot of work and is very pricey. If I was in your shoes I would keep the passive systmr and have your local hydraulic shop replace the rubber hoses for you. To get replacement jaguar hoses would be about $150 to $200 each last time I checked. Local hydraulic place you would be well under $100 for both.

I also think it would be more work to remove the oil cooler system as well. How are you going to block it off and block off the bottom of the oil pan?

To convert to full flow system you will need to get many second hand parts as not all are available new. All 6.0 have full flow (reason I am converting myself) however I am having to do custom lines as only 3 of the 4 lines are available and they are even more pricey ($500 I believe total) plus the oil cooler is $300 ( I purchased a great condition second hand one).

Only reason I am keepin full flow is because my 6.0 already has it. Or else in the engine you need a new pickup, oil pan, and oil filter assembly.

 

this 86 XJS has a transplanted 6.0L , added these hood louvers to vent out hot under hood
air, says it helped substantialy. also added a larger engine oil cooler than factory!

on my V12 i have tested temperatures ,and after a 1/2hr run, rear of heads are at 180-185F, but top of cam covers run over 210-220F, i am giving it serious thought about a larger cooler, already have a better trans. cooler.

admitdly i have had no engine problems, except NORMAL rear crank rope seal leaking oil.