In need of a new thermostat and I see some come with a rubber seal around the perimeter and some do not. Does it matter? Does brand matter?

My car isn't getting up to temperature and I assume the thermostat has failed in the open position. I shorted out the temperature sensor wire and confirmed the gauge is working, but the needle doesn't hardly get off the 50 mark. Tried two different temp sensors and they both read the same.

Fluke meter temps:
Radiator 94 degrees
Lower radiator hose 110 degrees
Upper radiator hose 89 degrees
Thermostat inlet 125 degrees
Coolant rail 125 degrees
Top center of head in the spark plug galley 190 degrees

 

do you mean the O Ring ? yes, it is needed.

 

This.

The rubber seal that goes around the thermostat. The one I took out of the car, 1985 XJ5, did not have this seal and adding it seems to me would stop the thermostat from sitting down in the recessed groove in the thermostat housing.

 

The light area is the recessed area I am referencing.

The thermostat that came out of the car without this rubber piece could possibly be the original one as the car only has 56,000 original miles.

 

There should be a gasket on the face of that t-stat holder. The thermostat itself just nestles into that recess, and no O-ring is needed. Of course an O-ring may be needed for a different car.

 

I concur. No o-ring used in this application. I'm pretty sure some of the XJ40s and X300s used the o-ring. For an older model it can be tossed into your junk drawer :-)

Cheers
DD

 

Due to teh fact Jaguar, and others very rarely specified simple things as unique to them, stats, temp sensers, temp sensors, etc etc, are used on many nmmakes and models.

Aftermarket regularly groups things in that way, so an o/ring could be supplied, wether it fits YOUR car is another discussion all together.

AJ6 had stat o/ring
AJ16 NO stat o/ring
V12' NO o/ring, gasket only.

That ledge the stat sits on MUST BE clean, so the stat sits nice and square.

Stat length is the most critical spec, and so many replacement stats are too short. They need to be 43mm fully open, and this applies to the XK 6cyl engine (S1,2,3) and all the V12 engines (except the carby version).

 

I ended up ordering a 180-degree fail-safe Motorad from my local Napa. I will have to check the length when I get it.

Am I correct in assuming the 43mm is the overall length once open? To test just drop in some boiling water on the stove and measure it once it is fully open?

 

Disc to disc, underside of top disc to underside of bottom disc.

OR

Measure the closed length, then add 8mm, that is the travel of thermostat wax bulbs.

Have a browse of this attachment. OK, its for V12, but exactly the same stat, as yours, just the real engine has 2 of them.

 

I must have screwed up big time because I installed a new thermostat with that seal around it in my car years ago. However no ill effects.
It seemed to keep the thermostat from dancing around and the seal fit perfectly in the notched area.

 

Would a 160-degree thermostat be ok, or should I opt for the 180-degree? I thought I ordered the 180 degree one, but what was waiting on me tonight at Napa was a160 degree one.

 

You want the 180. With the 180 you'll always be running warm enough to keep the fuel injection out of "cold mode".

Cheers
DD

 

I bought my first S3 XJ6 which was a repossession with the head off (and in the trunk), I sorted it out and got it running. Timing chains, tensioner and bent inlet valves etc.
But it was not too economical only doing 16 to 17 miles per imperial gallon on the open road and seemed to run cold.
Eventually I twigged that the thermostat was keeping the engine cold, and it turned out somebody in the past had fitted a 70C/160F thermostat.
I fitted the correct 180F/80C thermostat and average fuel consumption improved to 20 to 21 MPG
Cheers

 

That is what I was worried about with the 160-degree thermostat, that the car would not get up to its correct operating temperature.
Ordered the correct 180-degree thermostat and will be here after turkey day.