Correct thermostats

(V12 Dave) #1

I am in the process of sourcing thermostats for my 87 xj12 Cdn.
ordered and received 2 from a supplier that have a rubber gasket around the outer circumference, however the originals don’t have the gaskets. Checked out a couple of other suppliers and they quote the one with the gasket.
The gasket does not fit in the recess in the housing.
Without the gasket I am not certain the thermostat will seat and seal in the housing recess.
Has anyone run into this?


(DavetheLimey) #2

Yes, I have. I ordered a pair of 'stats from a popular supplier, and one came with a rubber gasket, and one came without.(Different diameters,too.) My originals had no rubber ring, so both went back, and I bought the correct units from another supplier.

(Aristides Balanos) #3

Mine have no gaskets either, 86 XJ12 Cdn.
It’s a tight fit and even if it’s not a complete seal the effect would be minimal.
More importantly, make sure that they have the jiggle pins and that the small plate extends far enough to actually close the bypass, if I remember correctly it must be +40mm when the thermostat is fully open.


(Doug Dwyer) #4

Age old problem. Lots of incorrect thermostats being sold for V12s, sometimes even sold by Jaguar specialists. Catalog errors and/or not understanding that the importance of getting it right.

IMO buy Jaguar-packaged EBC3576 (82º) or EBC3577 (88º) from a Jag dealer or specialist…which you might have to actually speak to over the phone to ensure you’re getting what you want and not an almost-close-enough-to-work substitution.


(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #5

Perhaps you’re supposed to cut the rubber seal off for this application?

(V12 Dave) #6

Thanks everyone, glad to hear I didn’t invent this problem.
The ones I am fussing with came from a reputable Jag parts supplier, but the confusion is still there.
The rubber gasket slides off and I checked the fit of the stat without it and it is verrrrry close.
My read is that by the time I add the paper gasket it should seal up.
It is 88deg with the jiggle pin and of very nice construction, better than the original.
I am inclined to believe it will get the job done.
Any other thoughts welcome.

Rewiring my injection harness today, good fun. I was able to source correct Bosch connectors and sleeves, high temp wire, insulated loom. Had injectors cleaned and tested by a local guy who did a great job. New seals for them as well.

To anyone who hasn’t rewired their injector harness on their V12 yet, I was appalled at how brittle my wiring was on a low mile car. Worst spot was mid way along the harness where the wires are joined in a connector and are doubled back on themselves in a 180 bend. Wouldn’t take much of a disturbance to crack the cover. So far not that bad of a job, although its not fired up yet!

Might have got a little carried away with it all but it’s quite rewarding to get this deep into it and see it all cleaned up and coming back together.
Gotta love this hobby!

(V12 Dave) #7

Oh ya, it is an EBC3577

(Doug Dwyer) #8

What’s the length?

The problem with many replacement is that they’re too short and/or offer incorrect length of travel. As a result the rear disc does not close-off the bypass port.

From memory the magic number is 41 mm from the rear disc to the backside of the main body.


(Doug Dwyer) #9

In Jaguar packaging?

Many suppliers use the factory part number for listings and invoicing…even if supplying a non-factory part.

If it IS in Jaguar packaging then it appears that Jaguar has ‘rationalized’ their offerings, condensing 2 or more different part numbers into one. Sometimes it doesn’t work out, sometimes it does!

AFAIK the thermostats with the rubber seal are for the AJ6 six cylinder cars…but don’t hold me to that.


(V12 Dave) #10

Thanks Doug, good info, and I’ll check on the length

(V12 Dave) #11

Back again with my thermostat challenge and attached is a picture of the old and new.
Old appears to be about 31mm long, new about 41mm.
As an aside I checked another well known supplier’s website and looks like they list the new one for my '87 XJ12 as well.
Black ring is the gasket that just comes off.

If I could find a supplier that shows something like the old I would just go with that.


(Doug Dwyer) #12

Since the thermostat is out, look into the hole and you’ll see the coolant passageway that needed to be blocked-off by the rear disc when the thermostat opens. Measure the distance from the surface that the thermostat sits and the passageway.

Now heat thermostat and when it is fully opened, measure the length. The rear disc needs to travel far enough to close-off the passageway


(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #13

I dunno where you’re measuring, but in the pic the distance from the mount flange to the disc that closes off the bypass looks exactly the same. The new thermostat looks to be significantly heavier duty.

(MarekH) #14

The presence of a jiggle pin or the lack a gasket if loose fitting will have the same effect. In any case, the gap around the perimeter where the gasket is would soon be silted up, so the gasket is almost certainly trivial.

For everything you need to know about thermostats, just enter the search terms “thermostat @marekh” into the search function. There are also pictures in my old photo albums which cover this ground.

kind regards

(V12 Dave) #15

Thanks Doug, good approach. I’ll do that today.

(V12 Dave) #16

Hi Kirby, the photo angle is not the best, measuring leads to the two measurements I quoted.

(V12 Dave) #17

So after following Doug’s suggestion, both stats extend far enough to comfortably seal the bypass and both appear to have the same flow area once the full temp is reached. Pictures attached.

The other perhaps obvious question is why do I feel the need to replace the old ones on a low mileage car that didn’t exhibit any problems with the stats?

Only reasons are they are 32 years old and I have everything apart
Barring any other thoughts I am inclined to use the new ones?
Thanks guys

(Aristides Balanos) #18

I would for sure use the new ones, you bought them, they work, they seem to have a larger opening, the are heavier duty and they are new!


(Paul) #19

? Why
The newer one appears far more robust…

…and the coolant passage diameter appears larger as well.

I would much prefer the new model.

Personally I’d do whatever it took within reason to make the new style work… But that’s me.

Edit: Excuse me, responded without viewing other replies.
Didn’t intend to pile on!