I'm going to be replacing the radiator with a single-pass unit in the near future.

An inspection from the bottom shows the support that the radiator sits on is rusting away. Is there anything particular about this support that would prevent me from fabricating something myself without much difficulity? I can't get a good look at it unless I pull the radiator, and I'd like not to have to do that twice.

Thanks,

John
1987 XJ-S V12, 62000 miles

 

I think that this may be the part that you are looking for, the front cross member.

 

Be aware that the lower radiator support is a structural member ans is welded into the chassis rails.
It wouldn't be hard to fabricate one, but ensure the chassis is braced well before removal and that the car is properly squared.
I replaced the lower rad support on my car, cut another good one out of another car, not a difficult job.

 

No, this bit is just a trim piece, essentially, that goes between the rad and the bumper, not the cross beam under the rad. As Typhoon says, the rad sits on a structural beam that ties the two lower chassis rails together. A new one can be bought. Often (not always!), it rusts out in the middle, and the ends that attach to the lower chassis rails are often fine. In this case, some decent properly welded patches or strips of heavy gauge steel will be a good repair.

Greg

 

Hey J_C_R,

Just curious what brand of radiator you're going to use when you replace the old one. I'm leaning in the same direction.

Thanks, Terry

 

Terry...I should be receiving this week the BeCool 62082 radiator. There seem to be several schools of thought on the issue, Kirby coming down on replacing the dual pass scheme, Emden saying just maintain it and all will be well, but my gut tells me to go with a single pass system.

It'll probably be a month or so until I put it in, as I'll want to replace the crossover pipe (got the copper, just need to get to work on it) and ditch the engine-driven fan for something electric.

So, we shall see how it all turns out...

John
1987 XJ-S V12, 62,000 miles

 

Crossmember not fitted:

Crossmember fitted:

Seriously, it's pretty simple to remove one for your car, drill spotwelds on outer ends of crossmember outside of chassis rails and cut donor car chassis rail above crossmember and in front/behind crossmember to remove it. Then simply grind off all remaining chassis rail off donor crossmember.
Then remove your old one by trimming back close to chassis and grinding the rest back to a nice clean chassis.

 

Can I ask why you want to go with single pass when ALL of the F1, V8 Supercar and NASCAR teams run multiple pass.

It makes the install messy with the need for a cross pipe in front of the engine. There is a guy here in Australia with a twin turbo XJS race car and he runs a STOCK XJS radiator (yes you read that right STOCK) after much experimenting with alloy single pass etc etc the car would overheat on the way up mountain straight at Bathurst. Now with the stock radiator he can do multpile lap with no overheating issues,, just my 2c

 

FWIW, my experience is that it is much more about airflow through, rather than than the type of radiator itself.

I am not surprised that the stock cooling is adequate for a racer, as if you remove the aircon condenser, and have adequate fans (mechanical or electric) no V12 XJS will overheat. Having said that, my experience is that with the aircon condenser in, the airflow in a standard HE is only just adequate in hot conditions and slow moving traffic after a 'hot stop'.

On my car (which has never overheated but which I wished to improve to give me more of a margin of safety) I moved the horns to each side, and moved the secondary coil under the headlight. This alone gave 20 more square inches of uninterrupted airflow to the rad stack. After this it was better after a hot stop, but still not as good as my Mondeo, as it took ages to cool back down to 'electric fan off' mode in the traffic crawl after a hot stop. Often not going into 'fan off' until the car speeded up.

So I did something else, having tested my theory with the front bumper off the car, I moved the plate to the side, alfa romeo style, and cut a slot in the front bumper about 17" by 3". Cooling absolutely transformed. back down to 'under the N' in no time after a hot stop, and almost instantaneously on speed up.



Now I am not suggesting anyone copies my slot, as it does change the look of the car, but believe it or not, in real life nobody notices or remarks on it, and I do not notice it when returning to the car. But I am suggesting that getting airflow to the stack and through the stack is crucial.

My car has the mechanical fan replaced by an electric that is triggered by the standard thermostatic switch in the water pump inlet (a Grant Francis modification). The standard electric is replaced by a more efficient aftermarket one, and is wired to come on with the aircon. No foam round the rad, as I believe the leakage is practically zero at speed, and obviously nothing at standstill with the fans on, and the flow round the rad keeps the engine bay cooler. Anyone who does not believe the 'zero leakage at speed theory' should think about the huge amount of 'excess air' that is NOT going through the rad stack at 30 mph and above, basically most of the air is being pushed aside by the car, not pushed through the rad. The main benefit of replacing the mechanical fan is 1.5 to 2 MPG, plus better cooling in traffic.

The extra airflow from the slot was proved when immediately the slot was done, the fan warning light illuminated at speed, because the fan's electric motor was "windmilling" and so generating enough current to light the LED warning light wired to earth!

Greg

 

Makes perfect sense, the XJS was not designed around the massive rubber bumpers it was forced to wear.

 

I am a new member but my 88 had overheating issues as well. After reading all the options I chose to go with an aluminum radiator in the stock configuration that I think I got from Johns Cars. It is a Wizzard unit. From that point forward I never had even the tiniest problem. I also installed filters in the cooling system. The stock setup works well as long as it is maintained. Of course this is just my opinion.

Rob

88/90 XJS

 

Warren..my car is much more likley to be sitting in traffic with the A/C on, which is not a state that I imagine many race cars find themselves in...I'm much more concerned about it staying cool at low (or no) speed than at high speeds. Without rehashing all the arguments Palm makes, I'll just say that they make sense to me, and that I think a simple solution (granted, not easy to implement, but I only have to do it once), i.e. running the coolant through the entire radiator once is better than a multi-pass scheme.

I'm not all that concerned about the plumbing, as I said it's a one-time task and I'll learn a lot along the way. And the stock fans will go away to be replaced by electrics which I may mount out front, which will give some room for the extra plumbing.

I really like Greg's cut-out bumper idea.

Regards,

John

 

My car with the stock radiator ( re-cored ) stayed cool in 40°C heat when stuck in traffic when I lived in Perth.

With regards to cooling the more passes (within reason) through the radiator the better the cooling, also flow has a lot to do with cooling do not run the flow too slow you want more flow for better cooling.

The radiator should be black as this will improve the heat transfer to air from the fins. I know most radiators these days are alloy and not painted this is because its cheaper to not paint them.

BTW that race car runs two massive intercoolers in front of the radiator. It's up to you if you want to go down the single pass route it will work. In my experiance if the stock system is up to par you will have no issues with temperature.

I just think it's a lot of work for little or no gain. A better area to modify would be the water outlets from the engine. This can alleviate the hot spots that can happen in the rear cylinders.