Engine cooling thermosats

[John Quilter]

I am wanting to change the thermostat in my S Type. The variety out there is a bit confusing. Looking for one that is 74C and I believe it should have a feature that blocks off the bypass passage when it hot and open. Here is one offered by Barretts and one offered by Welsh Jaguar. Which works properly? The link shows even more choices.

https://www.sngbarratt.com/English/#/us ... Down=false

[NigelW]

You will need the stat that uses a shield to block off the bypass slot.

[Glyn Ruck]

This is the correct thermostat. When open closes the bypass port and forces 100% of coolant via radiator. See 2nd item genuine Waxstat from Barratts.

Huey Thermostat.JPG (86.85 KiB) Viewed 3320 times

[John Quilter]

Well, back to my thermostat issue. I have ordered the type shown above in the photo with C3731 and pulled my thermo cover finding I already have that type fitted! But poking around with my finger I could not see how that small ring at the bottom of the thermostat, even when hot and extended, closes off any passage to the bypass hose that attaches at the bottom of the thermo housing. There does not seem to be any passage accessible with fingers at all.
I think I read somewhere, long ago, that some 3.8 engine folks have put a restrictor of some sort in the bypass hose to reduce the flow, thus forcing more coolant to the radiator. Ever heard of that? I guess I could experiment with a temporary clamping pliers on the hose and see if there is any difference. Thoughts?

[Glyn Ruck]

For racing the bypass was blocked ~ engines were seldom cold and frequently dismantled. This is the bypass slot the sleeve closes. Excuse my filthy spare engine.

IMG_20180317_095758 - Copy.jpg (3 MiB) Viewed 3236 times

[John Quilter]

Thanks, I was expecting more of a port like in the center of your photo. I did finally locate it. Some on another Jaguar forum, advocate for fitting some type of restriction inside the bypass hose with only a 1/4 inch hole in it. May try that.

[Glyn Ruck]

Don't unless you are racing it. You will cause uneven warming of the block & head. This can lead to cracked blocks & blown head gaskets. Ensure your radiator is in good nick or have it recored. Preferably with a tropical core if the engine is running too hot. I run a new uprated radiator & the thermostat keeps the engine UP to required operating temperature. i.e. I have excess cooling capacity. The radiator looks identical to the original. There is a lot of nonsense spoken on the internet. Sorting the wheat from the chaff can be a challenge.

IMG_20180308_180430 - Copy (2).jpg (655.44 KiB) Viewed 3207 times