Hi Folks,

I had my radiator rodded out. In removing it the foam bits at the edges broke up. Any ideas on how to get or make replacements? Thanks!

 

Forget about it. leaving it out does absolutely nothing to the cooling, and keeps the engine compartment cooler.

 

I got mine directly from JCP in the UK for a reasonable price. On this instance , I personally think they where put there to improve cooling and since I don’t have their testing capabilities, I differ to Jaguar on this instance. This is arbitrary on my part, however, as I do not follow all “factory recommendations” on other topics, for example, as the “lifetime” durability of fluids on my X type.

 

Jaguar Classic Parts gave me the part numbers (CAC2321 and CAC3129) but looks like they are no longer available, from them or anyone. Looks like they only recently ran out too. Darn.

-mB

 

I myself question the necessity of the foam. Still, I wanted to include it when I did my engine conversion a few years ago. As it happened I had a radiator foam kit for a Corvette and found that it would work with some minor trimming. I think the specific kit was for a 1970 model with a 454 engine.

Anyhow, just throwing this out there as a possible alternative source for the foam

Cheers
DD

 

when I cleaned up my engine compartment and engine, along with checking the wiring, I removed my radiator, condenser and oil cooler (to clean them out) Upon reassembly. I left the foam out as it was no good, and had no problem with overheating even on our HOT Nebraska day running the ac

 

100% correct. Omitting the foam keeps the engine bay cooler and does not adversely affect the cooling. Once the car is moving at 30/40 mph, there is a huge (but invisible) "pillow" of air being pushed in front of the car and trying desperately to get round it. This air mass is vastly greater than the amount of air that can get through the radiator, or past it down the radiator sides between the rad and the body. Therefore, the foam (the only justification for which is to dam up the air so that more goes through the rad) is unnecessary.

 

I too got rid of foam after re-coring the radiator. (The foam was crumbling in parts anyway.)

Though the improvement in cooling (which by the way was huge!) most likely came from re-coring and cleaning, leaving foam out does not appear to have any negative consequences. So, I agree with most — just leave it out

 

I don't have the foam either, and haven't had any problems. I mean, the gap's pretty narrow really.
In fact, I think leaving the foam off means it's easier for cold (relatively) air to get into the air intakes. Which in my early facelift at least, are pointed pretty much directly at the gaps.

 

Idk, but even in modern cars with electric fans, there is foam insulation around the radiator. The current F type has radiator foam insulation, look up the diagrams if you’d like....... There must be a reason why engineers are still doing this today. I won’t pretend like I know the exact details, but clearly, 25 years after the last XJS was made they still view this as a critical component in the cooling system. I would think twice before parting with it.

 

Perhaps there is a sweet spot between standing still, where no air is pushed through the rad, and moving fast enough to push a ton of air through the rad, where the foam can help push that 10% more air through the rad to keep temps cool...?

 

I suspect it is because modern cars are so concerned about efficient airflow and weight that: (a) their radiator entrances are as tiny as they dare make them, (b) their radiators are as small as they dare make them, (c) they want to control the airflow though the engine bay from an efficiency and silencing viewpoint, and (d) the amount of coolant in a modern engine is tiny. All this adding up to a need for ultra efficient airflow through the radiator.
I am not saying that under these circumstances, sealing off the radiator is pointless. I am saying on the XJS it is!

 

Like I said earlier, I do not have the knowledge, nor the testing capabilities that Jaguar has to be able to refute or agree with any of these points. All I can say is that cars before the XJS where putting foam around their radiators, and cars today continue to do so, even with all modern advances available, such as extremely powerful electric fans.. Perhaps on the the XJS it is simply there as an anti-rattle device, perhaps not. But I still maintain that the best option is to have the foam in place.

 

There is very little information out there on how foam seals help, mostly just flat statements that they do, by forcing air through the rad. Which, at any decent speed, would appear to happen by ram force, as Greg et al. have noted.
I did, however, find this:
(Source: RX8 Help)
So, if I follow that, having the foam doesn't prevent air going through the gap into the engine bay so much as prevent it coming back out. Again, I wouldn't imagine this would be easy at speed, but around town, stopped perhaps, I can imagine how the fan pulls in all this air through the rad, trying to create an area of lower pressure inside the engine bay, which fails as it keeps leaking out the sides. What I don't see is how the fan can create that lower pressure. It's pulling air in, I assume, based on the gale I feel when opening the bonnet while it's spinning, which would seem to create an area of higher pressure inside the engine bay. How much forward movement do we need to create a low pressure area under the car to suck that air out? And how much air actually does escape around the rad?

 

SD
At rest, fan blowing, air pressure is higher in the engine bay than outside; just as it is higher at the outlet of Madame's hair dryer than at the intake.
Once moving, the "bow wave" of air in front of the car creates higher pressure in front than behind the radiator. Allowing air to escape from the engine bay is crucial, obviously, or there would be no flow through the rad, just as there is no flow into a full bottle of water held under a tap. On the XJS air escapes from the engine bay under the car. In fact, as I have proved by measuring my own car's air temperatures all over the engine bay, radiator air mainly goes downwards between the rear of the radiator and the engine. This is because the air dam and undertray creates a low pressure area under that spot.
Grant advised me when I changed my gearbox recently to ensure the maximum gap between the box and the tunnel, as this also allows air to more easily escape the rear of the engine bay and thus create airflow through the engine bay.
The key is getting air out and in"! As long as it can get out, no serious "blocking pressure" will exist in the engine bay. As long as it can get in, no pools of hot air will be in the engine bay. As for your quotation (and I do not accuse you of believing it) "but then the air packs up the engine bay after flowing through the radiator, which limits how big of a pressure difference you can really achieve" the idea that the engine bay is so sealed that a gap by the radiator an inch wide all round will overcome the huge exit gaps all round the engine is fanciful, the idea that a 30 to 70 mph gale will be held back by this even moreso.
But, as i mentioned before, on modern engines with very little coolant in the system, and very little extra capacity in the system to absorb any sub-optimal system faults, the point made in the quotation may be apposite. On our cars, in my opinion anyway, the cooling/engine bay heat problems are all about:

• radiator airflow (blockages and poor intake configuration to the radiator)
• coolant leaks from poor hoses
• cooked wiring from closed bonnets after a hot stop

that is why i have addressed the first point by creating an extra air intake slot in my front bumper, moving the horns out of the airflow and moving (on Lucas cars only, like mine) the secondary coil out of the airflow. Together these mods give more than 100 square inches of extra clean airflow into the radiator. After a traffic stop in hot weather, my coolant temperature gauge starts to fall as soon as I get moving, whereas before these mods it took over two miles to start doing so.

 

At this stage I am searching for answers, or at least clues. Because my car has no foam, and in normal driving it's fine, so I'm curious as to why foam would be so all-fired important. But it can go over the halfway mark in heavy traffic with a/c on, or climbing a hill, and while it always goes down again, and while I've been told and now know that only a few degrees difference can cause the needle to move quite a bit, I'm never complacent and anything I can do to help cooling is better. I mean, I can prove my cooling works well because after filling up, the needle goes a fair bit to the right thanks to heat soak, but as soon as I move off and the water's circulating, it drops right back again. And when stopping the car after a run, if you get out before turning the engine off, there's an impressive amount of heat pouring up from the sides under the engine. So the hot air's being pushed out all right. I do wonder how much gap I have over the transmission, mind. If it has to come out again, I'm going to use Grant's suggestion of modern high-efficiency thin insulation.
The same RX8 site also said lifting the rear of the bonnet won't help cool the engine and could even make it worse due to that being the highest-pressure area under the bonnet, and so vents/grilles should be at the front, but even I could tell that sounded bogus. I've seen the temp gauge in my car drop when cracking the bonnet on a long slow uphill drive.

I do wonder about cooking wires under the bonnet. Like I posted a couple of years ago, I applied heat-sensitive stickers to various parts of my engine to measure how hot it got both during a run and afterwards, and the stickers I put on places that weren't directed contacting coolant (water pipes, basically) like, for example, the aircon compressor, showed no significant rise. So I think any wires that aren't actually running alongside the engine block--i.e. that are in the air or along the engine bay sides--will be fine.

 

Enjoying the debate, especially the thoughts on how to keep a low pressure environment on the engine side of the rad and whether the foams play an important role or not. I do remember on my Triumph TR6 how it had a series of cardboard panels between the inside of the external grille and the front of the rad which I guess was to funnel as much of the external air to force it to pass through the rad. The concept of trying to funnel air from a large surface area to the smaller surface are of the rad seemed a good idea, rather than just trying to seal the engine bay per se,

I haven't done enough mileage in my pre-HE to fully appreciate the principles of the cooling system, but what I have noticed is the heat soak that is still coming off the engine hours after I've turned off the engine. The V12 does seem to generate and hold the heat more than any other engine I've seen.

What I have seen on my AJ16 and other six-cylinder XJS is the importance of the cooling fins on the rad and their ability to control the temperature of the coolant. It seems that all of the cars can manage to keep themselves cool when they are moving, as the air flowing through the rad can dissipate the heat successfully. The issue seems to be when the cars are stationary, especially with aircon running. Then the only way that the heat can dissipate from the rad is via the huge total surface area of all the cooling fins. But so many cars have lost much of the cooling fins in the lower third of the rad due to rad debris etc being thrown at them. And then the car can't lose it's rad heat when at rest. In my case a new rad was the only answer and immediately resolved the problem.

Paul

 

I always thought the foam was to prevent the hot air from the engine side 'short circuiting' and being drawn back to the front of the rad (which needs to be cool fresh air) when the car is stationary. Many cars seem to have sealing panels around the rad between the front and rear of the rad and I always assumed this was the reason for it.
Whether a small bit of foam in quite a small gap is going to make that much difference is another thing...

 

Paul
One of the most spectacular bad rad pics I have seen!
As to airflow at stationary tickover: it is important to remember that the car does not know it is at tickover. The only difference as far as the engine cooling system is concerned is airflow. At above 30/40 mph the fan does very little, the cooling flow through the radiator is all about ram-air. At tickover, the fan has to do it all, and by definition an engine-driven fan will not be turning very fast and thus not pulling much air through the radiator. The fins can only dissipate heat if the air flowing over them is cooler than the coolant, gets heated and gets immediately replaced by more unheated air. So not much airflow = the air flowing over the fins getting heated by the coolant and staying in place. Thus not causing as much heat transfer as would happen if that hot air by the fin was immediately removed.
The reasons why modern cars all have electric fans are numerous: Cheapness, simplicity, weight, but also, most importantly, their ability to control temperatures independently of engine rpm. My ford Mondeo will tickover all day long, aircon on, because it has an electric fan pulling air through the aircon condenser and the radiator.
And so will my XJS. Years ago I fitted the biggest SPAL I could find in place of the engine driven fan, and mounted it half an inch from the radiator. This is in addition to the largest SPAL I could fit in afterwards to replace the OEM electric fan. It will hold a piece of A4 paper on the front side of the condenser when running at tickover, fan-on. If I stop in traffic and the main fan comes on (either by its thermostat or manually by cabin switch) I can watch the temperature gauge drop.
So airflow is the key, and anyone who really wants modern levels of coolant control at rest or in traffic, has to go for electric fans. Not that, I hasten to add, the OEM setup is not perfectly good and quite capable of ensuuring the engine stays cool enough. It just is that in modern conditions, with hot traffic stops, etc etc if anyone wants their engine coolant temperature to remain as controlled as a modern vehicle's is, and want their aircon to remain at top efficiency in the process, it has to be (for the V12) very powerful electric fans. (And a gismo to raise the tickover a tad when they are on so as to keep the charge up!).