Ineffective thermoswitch

[MilesA]

Like many owners, my car suffers from a certain amount of overheating. I have applied the obvious changes to minimise this but with modern fuel and Webers it will remain a challenge. One change is an electric puller fan wired to a thermoswitch in a Moss steel down pipe which is also wired to a separate dash switch.

 

As the fan was rarely triggered by the thermoswitch and not until the gauge read 95+ I thought that changing to one rated at low temperatures, 82 on 68 off should do the trick (and may be a little extreme - but it's all trial and error). So drained the system, fitted the new switch and ran the car on the drive watching the temperature rise to 90+. Fan not triggered. Flicked the dash switch and fan started. Removed the cables to the thermo switch and held them together - again fan started. So not a wiring problem. Given that is the end of my limited understanding, time to turn to the forum.

 

Given the engine runs so hot I cannot understand how this and the previous thermoswitch (86 on, 76 off) did not trigger or not until very high temps were shown on the gauge. I understand that there is a temperature drop of the coolant between the gauge sensor and position of the thermoswitch. Could it be that even passing through the rad, the coolant exceeds 82 (or 86) and so the thermoswitch remains off?

 

I can of course switch the fan on and off from the dash but constantly checking the temp gauge and flicking the switch does detract from relaxed driving.

 

Also, who supplies thermo housing gaskets of a decent thickness? I also replaced these having checked that the bellows thermo was working and the replacements were way thinner than those in place. I now have a leaking thermo housing so any recommendations welcome.

 

Thanks

 

Miles

[RogerH]

Hi Miles,

the thermo switch may well be working within its range. Your gauge may be out, they are not accurate devices.

 

You could place the thermo switch in a pan of water and bring it up to temp whist using a thermometer to measure the temp.

Is it possible to put the gauge bulb into hot water to see the effect/temp

 

Moss sell both thick and thin thermostat housing gaskets.

 

Roger

[Lebro]

Are you sure your thermostat is opening when it shoud ? If it stays shut till a hotter temp is reached, then the switch will not have any hot water passing over it. My "Otter" switch (in the metal pipe connecting to the bottom hose) is rated at 92° on, & 87° off It come on when my gauge get to around 195°F (90.5°C)

 

Bob.

[RUBY131]

Hi Miles, the 3a I have recently purchased has been in South Africa since 1959 and interestingly has the thermoswitch to the electric fan disconnected and instead is wired to a switch on the dash which works great. I now leave the fan on all the time and have few problems even in the hot weather recently Cheers Chris

[MilesA]

Thanks all.

 

I made the schoolboy error of assuming that both old and new components will work on a 50 year old car without more (I really should know by now).

 

So back to the kitchen with a saucepan, cooking thermometer, the thermostat and the thermoswitch. If they both work at the correct temperature then the gauge must be the culprit. Bit reluctant to disconnect the temp sensor from the housing unnecessarily as I think they are a bit delicate. At least recon' temp gauges are available.

 

Thanks for the steer on gaskets Roger. Thought Moss were the source of the one I had but couldn't recall where I got my supply from.

 

Yes, Chris, it will be the dash switch for the time being it seems...

 

Thanks again.

 

Miles

[Guest ntc]

Miles

Is the bottom of the rad getting hot?

[MilesA]

Neil

 

Didn't check but had given the system a hefty flush with a couple of bottles of Wynns and coolant flowed from the drain plug and bottom hose when I took it off. Think I know where you are going though....will double check..

 

Thanks

 

Miles

[BlueTR3A-5EKT]

I bought myself an infra red thermometer from Maplin. It works a treat and gives me a more confident feel when diagnosing temp gauges that seem to be indicating too hot or cold. Just point and read.

 

Useful when checking my own fan switch. I now have the Moss supplied Revotec item that fits in the lower hose. Not cheap I hasten to add.

Peter W

[MilesA]

Peter

 

That is the luxury option of course. Think I will scrape a few more knuckles before reaching for the credit card though.

 

Miles