the only issue I have with this setup is the AU part. Im looking for something I can easily get in the states.

I have no problem making a fan shroud or having it made for me. I found some high flow fans that are 16". It would be nice to have simple wiring instructions on how to wire it all using the existing water pump switch and/ or aux fan switch. I think this is where people get stumped. Maybe there is an old thread somewhere that should get bumped? I searched through several pages with a search in the xjs forum for electric fan.

 

The Flex-a-lite 295 is a perfect fit for the stock XJS V12 radiator and can be found at the usual online go-faster-parts suppliers. I happened to find mine used for less than half the retail price.

There was a slight clearance issue in regards to the depth of the unit on my car. I had to shave off an 1/8" from under the weatherstripping side of the fan shroud. Then, I had to cut the terminals flush on the fan switch (essentially making it a plug). The wiring was dead simple using the instructions with the supplied fan controller. Thus, the original fan switch and relay were no longer needed.

Not a huge job, but it does require a bit of patience and finesse like most other jobs on the V12.

 

The goal is to produce a slight vacuum in the engine compartment, then the air is sucked through the radiator into the area of low pressure in the engine bay, and exits under the car. That's the reason cars have air dams, is to create that pressure differential.

The area at the base of the windshield is a high pressure area when the car is moving, that's why the fresh air intake for the climate control is there. The higher pressure forces the air into the cabin. The seal at the back of the hood is to keep that high pressure air out of the engine bay, where we want low pressure.

If you think about it, louvers placed in the wrong place will hinder cooling, because you will have high pressure air going into the engine bay through the louvers, instead of entering through the radiator. The net effect will be slower speed air through the radiator and inferior cooling.

If you look at how tightly packed the engine bays of modern FWD cars are, yet they don't have overheating problems. In comparison, the V12 has lots of space for airflow around the exhaust manifolds for air to flow through the radiator and out the bottom of the engine compartment.

As long as the foam seals around the radiator are present, the rad itself is clean inside and out( debris often gets sucked in between the radiator and condensor) and the fan clutch is working properly, the V12 should not overheat.

I had problems with mine over heating in stationary traffic and I finally pulled the radiator out. The previous owner must have lived near the beach, as the fins of the radiator were packed with sand. Holding it up to the sun I couldn't see any light through the fins. Once I knocked all the sand out ( I must have got 2 lbs of sand out, it covered the bottom of a 5 gallon bucket) the temp gauge never moved, no matter what the weather or traffic.

 

makes sense. cracking the hood will allow air to just flow over the engine and through the radiator, making it less effective than sealed which forces the air across the engine where it is hottest.

so you want the seal and you do not want louvres just randomly placed without taking the negative pressure into account.

I noticed the lamborgini 400 gt2, in one of Leno's episodes, also has a seal around the hood, which made me think of this.

 

also, it changes based on speed. there's negative pressure when going slow and when in standstill with the radiator fan blowing out the front. when on the freeway you have massive amounts of air blowing through the front creating positive pressure. if the fan is on on the freeway it gets pushed out the sides or underneath, with the positive pressure keeping that hotter air away from the engine bay. if your hood is not tightly sealed it screws this all up.

louvres directly above the hot areas should be ok as long as they are not too big, as it takes in account the hot air rises. as long as they are small enough to not cancel out all the negative and positive pressure.

 

Have you guys read Allan's book where the race car blew the bonnet off ripping out the pins due to the pressure under the bonnet at speed.

One modification that is needed to the XJS is better air flow through the engine bay and air MUST exit upwards through the bonnet, not under the car as happens with the sealed bonnet.

The guys who race these in the UK cut a hole in the firewall so air can exit through the wiper hole in the scuttle. You can also remove the lip infront of the scuttle that the bonnet seal sits on, or move the catches up so the back of the bonnet sits a little higher.

 

Brilliant summary of the requirements Warrjon. 100% correct. I'm saving for some louvres.
Greg

 

Wouldn't that let outside air *into* the engine bay....rather than let hot air out? As mentioned, the vicinity of the base of the windshield/firewall/scuttle is a high pressure area once the car is at speed.

Back in the day the hot rod and racer crowd would duct their carburetor air inlets to the cowl/scuttle are to take advantage of the high pressure

Cheers
DD

 

Doug
If the vents are placed at the rear of the bonnet and are faced rearward they should draw air out from the engine bay not force it inward, they actually should work like a vacuum drawing air from in to out. At speed I don’t see a huge advantage
(but a little is better then none) then when in slow situations any venting is better than none, now that’s when we can hurt our cars.

 

Doug is correct ( as usual &#128521 but the thought is outside air being forced in from top/rear will force hot engine air down/out. Either way it would be a win/win weather it is being used to port out or draw in, that hot air is going to be forced out in the end.

 

If air is being drawn out through the vents with no chance of reverse flow it will certainly help but if any flow enters, whether it is forcing hot air out or not it will not help. Any air that enters the engine bay through somewhere other than the front reduces the amount of airflow through the radiator,not a good thing.

 

Gents,
Here is my modification for using a single pass radiator and a Chevy dual fan set up. The Y pipe is part number 115590093 for ford Taurus SHO upper. Works very well.

 

This is a great site for XJS mods. These guys have been racing these things for ages and have heaps of experience.

Jaguar XJS Racing Hire Car build Stage 2.3

 

Please excuse the question but the orientation of the Y looks to be wrong for direction of flow, was there a reason you went with that layout?

 

What radiator is that? Aluminum with plastic tanks?

Jon

 

The Y was installed using hoses I had from several projects, once I find the correct hoses the orientation will be fixed. I had to start it asap!


The radiator is a ford big block, aluminum with plastic panels. I was looking for something inexpensive to start the project.

 

You have a part number or model number on the radiator? Did you have to modify anything to make it fit?

Jon

 

Jon,
The radiator is part number CU556, purchased at the local auto parts. no modifications were needed. It is taller than the jag, so I am working on the upper radiator support.
It works very well and is keeping the jag cool here in Florida.

 

This discussion by Roger Bywater ( former Jaguar Engineer) is quite fascinating on the topic of the 1 1/2 pass radiator: JagFORUM Logon

 

I for one agree with him. V12 jags for 35 odd years running factory configuration (tweeked around the edges with electric fans and ally radiator) without an engine overheat.