Hi all,
I have recently completely overhauled the cooling system in my 1982 HE (new aluminium large core rad, thermostats, sender, expansion tank, water pump, aux fan etc etc). Ive noticed the viscous coupling fan coming on a lot in slow traffic since the upgrade, I am guessing the greater heat dissipation abilities of the aluminium radiator is causing higher engine bay temps and switching on the clutch- the coolant temp itself is rock solid on the move and drops quickly once I assume the stats open in traffic. Where I live the current ambient temps are still mid teens C so the viscous fan seems to me to over-reacting, is this something that can be made less sensitive, it's quite noisy around town?
Thanks,
Matt

 

I'd be grateful to know it's really working !

I can't think of any way to adjust the engagement.

Maybe find a different spec clutch?

Cheers
DD

 

Yes fair enough! It's actually very comforting to know I am really well covered by cooling (even the AC functions so much better with the upgraded Aux fan)- I will have no concern on summer trips to hotter climates. I may try a different clutch as you suggest..

 

Leave well alone!

 

Haha, sounds like the voice of experience!

 

Indeed Matts, bitter experience!
See what happens in London traffic in the summer before changing anything, is my view. Also, have you renewed your thermostats recently? If not, 82° ones I would suggest before anything else is touched. Manners have them, quite cheap too. talk to Jack Westion there.

 

I have new thermostats from about 5 months ago (I believe they are 82 as the gauge sits below N even in traffic with viscous fan cutting in). Also new sender, gauge, expansion tank, radiator, hoses, aux fan upgrade and the viscous fan clutch was changed 5 months ago. We even did the water pump and aux fan otter switch The cooling system is entirely new basically.

 

On a warmish day driving today (23c) my viscous fan is running in 30mph/40mph traffic, that cannot be right...

 

Rumor has it that in the process of the V12 turning fuel into heat and noise it loves any speed above 30 MPH. Under that and stop/start traffic for a while, the car wants to produce steam.
Mine boiled in the stop/start traffic heading up to the Gothard mountain tunnel one bad hot traffic day. Had to pull over for a while. Has got very warm a few times but the last attempt to make boiling water for tea was in NY on I95 heading to the George Washington bridge. Traffic was slower than a snail with crutches. Luckily a cut out/layby came up and i managed to wait until it cooled down and the traffic subsided. I found out that NY has a lot of tow trucks looking for business. Lol
Upgrading my system to dual Fans and so is long overdue. Florida summer starting.

 

But just to be clear, my coolant temp was well below N at all times, in other words, the engine/coolant didn't appear to have been anywhere above normal operating temp

 

I don't know any way to change this except to find a fan clutch that doesn't engage until a higher temperature is reached.....while still being the correct size and fit for your XJS.

I haven't researched the matter but I don't recall such info typically being published by vendors or manufacturers.

In any case it's better to have a clutch that engages too early than one that engages too late !

Cheers
DD

 

Why not? What is the problem?

 

Hi Greg, shouldn't there be enough air flow at those speeds to cool the radiator without the need for the viscous fan cutting in? I wasn't nailing it, just cruising along at 30/40 in traffic (the AC was on incidentally) ?

 

A suggestion, and based on actual.

Check the airflow OUT of the engine bay.

The TH400 has a thick foam pad, glued to teh tunnel, above the trans. Glue fail, pad drops, and sits ON the trans, airflow STOPS. Air may be trying to get in the front, but if it cant get out, you have an air stall situation, usually AT the radiator. The mechanical fan will force it out, sort of.

I would NOT rely on the dash gauge, too long for here, but a proper mechanical gauge is the only way to see what is actually happening.

I fitted a "new age" thin insulation pad in there on all mine. PITA with the trans in the way, but doable. I was smart, did when the engine/trans was out, I took care of a few things/.

Yes, around 30Mph is deemed more than enough to keep the beast cool. Mine are all Efan cooled, with the RH being thermo (using the OE pump Inlet switch), and the LH is AC only.

Summer here, 40c plus, and the AC is ON, the thermo NEVER cuts in.
AC off, and cooler temps outside, the thermo RARELY cuts in, and only for a few seconds at a time.

There is more in the sticky at the top.

Always ask if still uncertain, no issues from me.

 

Assuming all crud cleaned out and new rad, I would check Grant's gearbox foam point, very important. After that, I would drive the car and see what it does for a few thousand miles. I assume the chin spoiler and undertray are in place properly?

 

Thanks Greg and Grant- one more piece of information: visco fan, sender, thermostats, new gauge etc. all fitted 5 months ago, three weeks ago I had brand new large core aluminium rad and aux fan (which runs constantly), water pump, otter switch etc etc. Since the last piece of work Im getting lower readings on the coolant gauge once thermostat opens, as you would expect and it stay low even in traffic. I understand they're rubbish but the same gauge is now reading lower, which has to be good. I was thinking I ought to double check that the new aux fan is a puller (!?), but otherwise can't understand as I should have a totally functional new cooling system at this point and it does sound like the visco is over-reacting.

Tbh I just assumed that the new radiator is dissipating so much more heat than the old blocked up one and that the viscous coupling is expecting hence triggering it unnecessarily (its ambient heat rather than coolant I think that triggers it?). Thanks for the tips.

 

Yep.

I have never bothered with alternative viscous units, just went Efan.

The fact your Aux is always running is odd to me, and accept that is the way it was set up, but then the Otter would be redundant.

Too cool is bad for that engine.

Remember the HOTTEST part of that radiator is the RH side, where the B Bank joins the A Bank flow, and right there is the fan hub.

 

* sorry should have said “runs constantly with AC on” I think all the really HEs did that . It’s off when the AC is off.

 

Correct, at least on the early HE cars such as yours. Later I think some other operating schemes were used. Maybe 1990-ish ? (I'm on my first cuppa coffee)

Cheers
DD

 

The HEs, pre Marelli at least, were wired for the Aux fan to be on all the time the aircon compressor is activated.
Additionally, the aux fan would also come on if the pump inlet spout thermostatic switch closed at its set temperature.