82C/180F vs 88C/190F thermostats

I don’t think two water pumps in the top hoses is a particularly good idea. On the s3 etype, the top hoses are at the level of the bottom of the header tank and the header tank is typically half full in normal operation. Fill it up any more and the water just gets expelled. I’d place the pumps lower down, where they will be guaranteed to be underwater.

My experience is that under steady state conditions, the temperature yo-yo’s by 6’c (from the thermostat spec’ temperature as its base), so running 88’c vs 82’c thermostats isn’t particularly noteworthy. It only becomes a big deal if the radiator is faulty - then you have lost about 50 seconds reaction time, as that is roughly how long it takes to raise the coolant temperature by 6’c on a running engine (measured at idle, which is when cooling is more marginal than when the water pump is turning faster and the car is moving).

What is important is how fast the radiator can stamp any excess temperature back down, but that’s a separate point, covered many times here already in other ways.

If the O.P. is worried about spiraling hot shutdown temperatures, read my post about heatsoak. The “method” works.

kind regards

The LT1 sourced from a 94 Cadillac Fleetwood Brougham features this reverse flow concept.

Used in my 83 XJ wuzza 6. Electric water pump in my application. a solution to a near disaster…

Allows more advance in timing.


Follow up for the archives…I’ve pulled my Waxstat thermostats, testing them in boiling water, and found that they only move 1.525" instead of the required 1.625". So they were not fully closing the bypass. They were only 2 years old.

They had come in a Jaguar bag, so I never checked them new. So they may have not been up to spec.

I have switched back to 180F thermostats, Gates 33188S. They are stamped Motorad in a Gates box, but that’s for another thread.

There is some mis info in the thread about certain higher temps being bad. Not so fast: Each engine design has a factory spec optimum operating temp…higher than THAT is less optimal, and lower than that IS less optimal. Back back in time…manufacturers specified a different thermostat for summer-winter temps in places with large variation…so as to maintain closer to optimal operating temps. Owner modifications to make an engine cooling system run cooler…than the optimal, thinking this will lessen overheating, are mis-directed. If overheating in normal driving, normal temps, there is an issue somewhere in the cooling system or engine tune, or engine or any combo. Changing a thermostat to remedy is not the answer. A thermostat regulates–its job is to allow cooling when coolant temp gets to warm, and to heat when cooling temp is too low.

I agree. But the HE V12 factory spec was pretty much 180F or 190F. The US spec was 190, the European spec was 180. I believe a lot of the reason for the US spec was for emissions.

High temps can be bad after shutdown and the heatsoak that follows, that’s my remedy. If I shut down at 185F versus 195F, probably not much difference for valve seats, but it may make a difference to fuel rail, heat in the Vee, etc. Temps can easily rise by 20F after shutdown. I’ve measured.

From what I have read from Jaguar on the subject the 82 C thermostats were recommended for the carburetor versions of the V12 engine and the 88 C ones for the fuel injected engine, but both were OK to use. I have the 88 C ones in my 1991 XJS V12

After a couple weeks, my engine is running just the same at 180F vs previous 190F. About the only difference, i believe my mpg has gone down 1mpg. This summer, i will see if heat soak is improved.

It means that the engine likes the 190F better Greg…

No, it means my engine is living a richer lifestyle :wink:

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Greg’s engine is now living the Lifestyle of the Rich and Famous

You don’t sound very sure :). How carefully did you measure this? Any number of variables could account for a 1 mpg difference, if that’s what it really is.


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Only one fill up. I need more months of data. Simple miles driven / gallons added. My trip computer went out with DOS.

I prefer the 180F, even if engine runs a wee bit richer. This is mainly a winter issue. During summer months, my engine will happily creep up +15F over thermostat temp.

One additional ‘Dang, they are going so slow they might as well be parked … no traffic behind, so …’ and there goes that 1 mpg.

Doesn’t take much of a twitch on the old throttle in these cars to get around slow people.

You would basically have to set up a test course, with no traffic or other variables, to actually assure a 1 mpg difference was, in fact, a 1 mpg difference.