tr3 Thermostats

[Lebro]

Having just read in full the "TR Basic Maintenance" section in the latest TRaction, there is one area I was not happy about.

The bellows type water thermostat with the shielding ring.

As I understand it the function of the ring is not to allow faster warm up, but to shut off the bypass circuit when the temperature becomes above "normal" in order to make sure that all the pumped water then passes through the radiator, thus ensuring maximum cooling effect. In practice, as the engine warms up, the thermostat will shunt water either through the bypass, or, the rad, or both depending on the exact temperature.

 

In every other area of the article I congratulate the authors on a job well done. It is a document of great use to both novice owners, & those who have done it all before - to act as a check list.

 

Bob.

[peejay4A]

That's my understanding too Bob.

[bigmalcy]

On a related subject, I have gone down the route of inserting a restrictor into the bi-pass line because I am using a non-bellows 'stat. Last year I found that (even in frigid Scotland) it wouldn't take much to send the temp up high enough to trigger the Kenlowe (slow crawls through villages / traffic lights etc).

 

Having fitted the restrictor and also the radiator cowl, I now find that the temp gauge sticks like glue to the '1' in 185, only rising to the middle of the temp gauge when stopped for a prolonged period. The 'stat in the car is the standard (not cold but not hot climate) version.

 

So have I made the cooling too effective, or is the temp I am running at ok?

[Lebro]

It sounds like everything is as it should be. The restrictor will speed the warming up, & improve the cooling once the thermostat has opened.

These guage's are not particularly accurate, but the fact that it goes to the "1" of 185 & stays there suggests that the thermostat is doing it's job very well.

 

I had two capilliary gauges to choose from on my recent re-build, I decided to test them off the car using a jug, & a kettle. They both were considerably in error, & in different directions ! I then chose the better one of the two condition wise, & re-calibrated it. This consists of getting the water in the jug to 185°C using a digital thermometer to check, then tweaking the needle on the guage till it read the same. Unit is now in car, & with a NOS bellows thermostat (with shield) the car comes fairly quickly up to approx 183° which I am quite happy with.

 

Bob.

[ianc]

Bob

I don't have a shield-type thermostat, but I understand the logic of what you have said, and I have a feeling that you are correct - I will check and, if necessary, will issue a correction as soon as possible.

It just proves that, however hard one tries and however much checking is done, something will get through!

 

Thanks very much for your kind words all of us (Tony, Roger and I) have been very pleased at the reception given to this Pull-Out.

 

Might you be the Bob Lebrocq (sorry if spelling incorrect) who was a member of the TVG some 40 years ago?

 

Ian Cornish

[Lebro]

Yep, that's me.

 

Got re-united with my old car 2 years ago, total re-build last year, on the road since September.

 

Bob.

[RAHTR4]

Something I think worth noting in relation to the original bellows type thermostat.

 

Quoting from a period AC technical publication - "if a bellows thermostat should fail in use, it will do so in the open position" - therefore the engine will still have water flow and thus not overheat.

 

It further states - "A wax pellet type thermostat will fail in the closed position" - not so good as with no or restricted water flow, the engine will definitely be at risk

 

Regards, Richard

[RogerH]

Hi Richard,

I can vouch for that.

Last year my Saab 9.5 had a thermostat failure and indeed it was in the closed position.

This then lead to a mass exodus of pound notes form my wallet (plus some moths).

If the temp gauge says aarrrgghhhh then stop immediately.

 

Roger