I was surfing EBay today and saw this item:

http://m.ebay.com/itm/370969812409?nav=SEARCH&sbk=1

I was wondering in relation to lowering the temp on my 1994 XJS 2+2:

1. How much difference this would make.
2. If there is anything "special" about this as opposed to any other thermostat.
3. How difficult would this be to change.

Thanks

 

Lowering the opening temperature of the thermostats will make NO difference to the operating temperature of the engine (so long as the thermostats are working).

Engine operating (coolant) temperature can anywhere between 90 to 110°C. The only function a thermostat controls is the warm up process.

Engines these days run much warmer than older engines to reduce emissions and increase thermal efficiency. There is no problem with an engine running warm as long as it does not lose coolant, ie boil over.

 

If you are happy with the way your engine runs then I wouldn't change the temperature of the thermostat,

If you absolutely must for whatever reason then you should know that the thermostat is designed to bring the engine at operating temperature as soon as possible to achieve optimum fuel economy as soon as possible. By putting a lower temperature thermostat you are theoretically lowering the amount of time it takes the engine to reach that operating temperature, and not lowering the operating temperature, which hurts your fuel economy and performance for a short period of time.

These engines are not fuel of computers monitoring them as new cars are so I don't think you should notice a difference, unless you count mile by mile how much you spend on gas and hook it up to a dyno. Hopes this answers the question.

I edited this post i made a small mistake

 

forgot to answer your last question. Is not that hard to change, just remove two bolts, pull it out, clean the surfaces, put the new one in, and make sure you put some rtv silicone and tighten those bolts.

How hard it is to change depends on how corroded those bolts are, look at them Best of luck!

 

There is no benefit in operating an engine at 71*C (160F) or attempting to do so.

Engine efficiency increases with higher running temps, the exact opposite of common myth.

 

In theory a thermo can do more than simply establish minimum operating temperature.

IF the cooling system is good enough then the thermo will always be gradually opening and closing and the coolant temp will 'hover' at whatever temp the thermo is rated at. Many cars, including Jags, can achieve this..... in mild conditions.

In conditions of high ambient heat, city traffic, or such, the cooling system may not have the ability to keep the coolant temp within thermostat control range. In those cases the thermostat will stay wide open....and how high the temp eventually gets is entirely up to the ability of the cooling system.

If your engine wants (for whatever reason) to run at (let's say) 100ºC then it makes no difference if your thermo is rated at 70, 80, or 90ºC. Any of the three will be wide open before 100ºC and no longer controlling anything.

The Ebay listing is a bit misleading in stating that the lower rated thermo will "maximize" your cooling system. Not sure if I agree with that wording. Later the listing correctly states that the lower rated thermo will simply open sooner.


Depending on the situation there can be some advantage to a cooler thermo. It can delay the onset of the coolant getting hotter than you want. But delaying isn't the same as preventing.

I think 71ºC is too cool. It might keep your engine in the cold enrichment phase too long.

Your original thermostat is probably 88ºC or about that. If you have no problem staying reasonably close to that temp then there's no advantage to a lower rated thermo. And if you're going wayyyyyy beyond then you have A) a cooling system problem or B) your existing thermo is stuck

Cheers
DD

 

Thank you all for sharing your knowledge so freely. I bought my car because I have always lived them, but I also realized that in order to afford to own one I was going to have to try my hand at some minor mechanics. Given my very limited mechanical knowledge I have found this forum to be an invaluable place to throw out ideas and ask questions, without people pointing my ignorance. THANK YOU!!