Classic cars forum & vehicle restoration.

RogerB · Posted: Thu May 10, 2018 8:30 am Post subject: Thermostat testing.

I have a 4lb pressure thermostat in my 1957 Standard 8. Going out last Saturday in the hot weather the car got very hot and stopped. How do I test the thermostat to see whether it is working properly?

RogerB

Rick · Site Admin Joined: 27 Apr 2005 Posts: 22437 Location: UK

An initial test would be to pop it into a pan of water and bring it to the boil, and see whether it opens up or not.

It may be worth checking that the rad's not blocked too, I recently had to replace the rad in my Minor as with the engine up to temperature, only the central third of the core was getting warm, the rest was stone cold. The problem hadn't manifested itself before, but during a journey on a hot day things got too warm under the bonnet.

RJ
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alastairq · Joined: 14 Oct 2016 Posts: 1950 Location: East Yorkshire

Remove thermostat, pop into saucepan of cold water....heat up & bring to boil, watch for thermostat opening.

Recently had thermostat issues with a neighbour's vehicle....turns out there are two sorts.
One sort remains closed when they fail....the other sort opens when they fail.

So if a stat is seen to open in pan, don't assume it's actually OK.......place in cool water, see if it closes again?

This issue raised another one....not sure if there's any way of telling [from photos, etc] if a stat is a closer, or an opener, when it fails?

Thus, many cheap stats [on ebay, amongst other places] may simply be old stock?

In the meantime, to keep running, cut out a [triangular? Only three cuts then?]....bit of flat steel.....drill holes to match thermostat cover...and also drill two or three smaller holes in the centre....
Couple of gaskets, and bolt in place....engine will take a bit longer to warm through.
[I did that decades ago on my Sprite...and forgot about it...it was sold like that....]

47Jag · Posted: Thu May 10, 2018 10:04 am Post subject:

Alisrair,

The t/stats that fail closed are the wax pellet ones, the older ether filled bellows type fail open.

Art

alastairq · Joined: 14 Oct 2016 Posts: 1950 Location: East Yorkshire

MikeEdwards · Joined: 25 May 2011 Posts: 2467 Location: South Cheshire

Am I reading that correctly? A thermostat that opens based on pressure rather than temperature?

If so, then this is one of the reasons I browse around forums like this one to learn about stuff that's different to what I'm used to. I still don't really know how a magneto-based ignition system works in comparison to a points / coil system (and many might argue that I don't know all that much about the latter) but I bet I could find something on here that covers it.

If not, then as you were everyone, stick the stat in a pan and see what happens.

alastairq · Joined: 14 Oct 2016 Posts: 1950 Location: East Yorkshire

I think the stats that fail and open simply have their springs on the opposite side?

RogerB · Posted: Thu May 10, 2018 6:00 pm Post subject:

Thank you all...

I put the thermostat in a bucket and poured boiling water on it.....

The copper end poppeth out.....eventually....!

I'm assuming that it works now?

RogerB

Bitumen Boy · Posted: Thu May 10, 2018 6:55 pm Post subject:

Ideally you should test it by heating from cold with a thermometer. Just because it opens doesn't mean it's opening at the correct temperature.

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

I think the OP has thermostat confused with radiator cap -they are pressure sensitive.
jp 26 Rover 9