The 'E' Type Forum

Hi all, i’m going to be changing a core plug soon and as I've never checked to see what thermostat i have in the car, thought I’d buy a new one and replace that at the same time. Another reason for replacing is that my temp gauge shows a slightly low reading 50degs most of the time, although in hot weather and traffic it can go to 90degs, so it hardly ever sits it the mid (70) position.
I did a bit of background reading and purchased C3731/1* from SNGB (their recommended option), the other choice was C3731/1W.
As I understand it it’s important the sleeve doesn’t block the by-pass channel when cold, and the depth of the channel from the base of the housing needs to be 11mm +.
The sleeve on the thermostat I’ve received sits a few mm down from the face of the housing so the sleeve extends 13-13.5mm down from the face.
So the question is, have i got the right thermostat or is the by pass channel likely to be covered by the sleeve when the water is cold? It’s probably going to be hard for anyone to say for sure, but if it doesn’t look right I want to take this up with SNGB before i flush the old coolant out.
Thanks

The C.3731/1 is the correct one. Check out this definitive article on E-Type thermostats and hopefully it will answer your question:
3.8: https://www.coolcatcorp.com/thermostats ... ifold.html
4.2: https://www.coolcatcorp.com/thermostats ... ifold.html

Darryl...your thermostat dosnt look closed....it has a gap thus giving you 13mm if completely closed it would be more like 11mm.... Steve

Heuer wrote: ↑

Wed Apr 24, 2024 2:33 pm

The C.3731/1 is the correct one. Check out this definitive article on E-Type thermostats and hopefully it will answer your question:
3.8: https://www.coolcatcorp.com/thermostats ... ifold.html
4.2: https://www.coolcatcorp.com/thermostats ... ifold.html

What is interesting in the 3.8 link above is it refers to the overall design of the thermostat and its siting as a reason for the 4lb pressure cap. However, this was raised in March 1963 to 9lb (Service Bulletin D.8) but I can find no corresponding changes to engine thermostats apart from in Nov 1962 (SB D.5 (2nd Issue)) where a change to C.20766 took place.

That’s what I think Steve, with no gap between the sleeve and the face it would be more like 11mm. I’ll give SNGB a ring tomorrow and see what they say

The only changes I can find at the time the rad cap was increased from 4 to 9 lbs in 1963 are a new (non convoluted) top hose and a small change in the position of the top hose fitment to the header tank. As mine is a late 3.8 it would originally have come with a 9lb cap and in any case I have a larger than original rad, coolcat fan and fosseway hoses so quite a few changes to original spec.
Is there any advantage in running a lower 4 lb cap other than possibly reducing the weep from my leaking core plug (which i intend to replace anyway)?

I have SNG C3731/1* fitted and the car runs very cool. I'd prefer it to open at a little higher temp

Michael Franck (Coolcat) had available a number of NOS thermostats and offered them still recently:
https://forums.jag-lovers.com/t/group-b ... /440914/39

They are the real stuff.

Thanks for the heads up. I’m currently waiting for SNGB to get back to me on the sleeve dimensions issue (13mm v 11mm). I will find out in a week’s time which thermostat I'm currently running and be able to take a view on whether to fit the new SNGB one or not. I have the same problem as Swindler with the temperature gauge reading low.