On a related topic; my 1985 car came from the factory with a rather old-fashioned oil cooler (the item under the condenser in front of the rad). It was a tube about 1 inch diameter with loops of thin wire welded to it looking like a long thin hedgehog. The more modern cars have a conventional looking cooler, as does mine now.
The point is this: the older style of cooler did not, repeat not, fill the gap below the condenser. There was loads of free space top and bottom of it for air to directly hit the radiator fins. In my mind there is no doubt that the older cooler allowed better radiator cooling than the modern style oil cooler does, purely because of better airflow.
As soon as I fitted a new modern OEM oil cooler, my car ran hotter; not overheating mind, but hotter. I did not like this much, so I removed the bumper and tested the car. INCREDIBLE! coolant temps were far lower. Anyone who does not believe it, just try it.
So, bumper back on, I cleared the air path as much as I could with a slot in the bumper about 18 x 3 inches and I moved the horns and the auxiliary coil out of the airflow. In total these mods gave over 100 square inches of clean airflow (rather than turbulent airflow) hitting the stack. Moving the coil and the horns alone gave about 40. These mods made a huge difference, particularly to the speed with which coolant temps reduced after a traffic stop, once the car got moving. "Clean" air hitting the rad stack is the absolute key to improved cooling, once all the basics are fixed.

 

Would I be correct in assuming that the facelifts, without the front coil to get in the way, would offer better cooling?

Also, with the better airflow, is that just air getting rammed into the rad, or does the fan actually pull enough even at a stop for opening up the front (bumper holes, etc.) to make a difference?

 

Presumably, slightly; but the front bodywork of the later facelifts is different, so I cannot say.

The bumper slot makes a huge difference once moving. None or not much at rest, I would think.

 

Thanks for your replies. Mine's an early facelift, before the bloated bumper, so I assume it's essentially the same as the pre-facelifts, with the only difference being the grille design. There's quite a large, open space in front of the... aircon cooler? Oil cooler? Can't remember what the large rad in front of the main rad is. At any rate, there's a fair bit of room for air to move in there.

 

Can you post close up pics of the bumper mod? I've wanted to do the same thing.

 

The one in front of the coolant radiator is the condenser for the air conditioning system, the oil cooler is much smaller and mounted lower down. I'm assuming by open space you mean deck space, like what the coil rests on? This is just part of the design of the front end, the rads are fitted as close to the engine as possible to maximize space, so you are left with some blank space up front.

As long as everything is up to factory spec, the XJS should cool just fine. I've driven in stop and go traffic in Miami as well as 130+mph for stretches on the highway without any cooling issues. Nowadays you can buy a beast of a radiator for only $200-300 bucks. I would definitely pick that first over cutting holes or adding dual electric fans, if you want to go past factory spec.

 

Condenser, that was it. Thanks. I'm not sure where the coil in a pre-facelift is, but probably, yes. Seems they could have shifted the condenser cooler a little further forward, made it easier to check the main rad condition, but perhaps they had their reasons.

The first thing I did for my car was order an aluminium radiator from Wizard, along with new 88-degree thermostats, hoses, and a new main fan. So long as there's enough coolant in the system, stopped in summer traffic the car will reach a needle's width past the middle, but stop there (generally!). These days, as it's only very early spring, she drives along distinctly on the cool side.

 

Is there any downside performance wise to this running 'cool' ? You'd think 90-degrees would be where you'd want it at regardless. I know my car has an entirely different personality once warmed up its not like modern vehicles that just GO from dead cold.

 

I should add that when I say "on the cool side" it's only a couple of needle-widths at most to to the cold side of the middle. If you go by the later facelift gauge, with just one single "normal" zone flanked by "cold" and "hot" it's still firmly in that "normal" range. It's just a reflection of the fact that the engine is getting cooled more by the colder air we have now than the hot muggy air we get in summer. And generally after about 30 minutes of town driving she's up to precisely halfway anyway (though drops back a little at speed).
But it is more reassuring than having it running on the other side of the middle mark....

 

Broadly speaking, 180-200şF (82-93şC) is where most modern (post 1950s, let's say) engines like to run in terms of overall efficiency and longevity. Jaguar used both 82şC and 88şC thermostats in the V12s.

The main thing to avoid is the 'cold enrichment' for any long period of time. The cold enrich tapers down quite a bit as the engine begins to warm up and is pretty much all done by the time coolant reaches 150şF or so (70şC). Even with an 82şC thermostat you're well out of that territory

Cheers
DD

 

i use a standalone engine temp gage,Digital readout in 2 degree increments, most important coolant sensor mounted on left /rear cylinder heads(tossed out the sticky AAR valve), 180 stats, and use outside trans cooler,.

never in 24 yrs have temps beyond 195F even in 100+ ambient!

average is 185F 95% of time.

you can flip the pic !!!!Grr.

 

Where is your sensor located and the readoutscreen ? I've been debating what engine related mods to do on the car now that I've got the rear end parts sorted (shop time pending) and I was thinking of fitting a series of digital gauges to a LCD screen either inside the center console/armrest or in the same location as the trip computer which naturally doesn't work anymore.

 

Here is the closeup, rubber cover over bumper off at this experimental stage. In the end I slightly reduced the width so I could get the license plate up on the LHS side of the bumper, as when I first slung it below it ruined the stability as it affected the airflow to the spoiler.

 

Ruined stability how?

I've thought of either having a shop fabricate a slightly larger front spoiler or your method with the a vent in the bumper, didn't the race cars (twr) have larger spoilers?

 

Because I had the license plat fixed below the bumper to start with. It interfered with the airflow to the spoiler. Once I moved it up so it was on the bumper, but to one side so the slot was unblocked, all good. If you look at the photo in post 33, you can just see the plate hanging below the bumper.