strange temperature fault

[Aussie John]

Had the Griff for 12 years; driving to Burghley and temp sitting on its usual 80, it suddenly went to over 90 and fans came on [while sitting on a steady 70mph on m62]. I pulled over and checked for coolant leaks [none] so continued on my way and the temp. returned to normal and never changed again. Could a thermostat cause this strange behaviour? Any thoughts guys? cheers, John.

[TVR Beaver]

not if the fans came on... the whole system must have been up there?... were you following something that could have taken your air flow?.. it wasn't that hot at weekend, but I've been on the motorway before, sat at 70 and seen the temp gaugue go up?... Did a bit of plastic or something cover your rad for a period of time?.....

[Aussie John]

Thanks for the reply John, I was not behind anyone and didn't see anything blocking the rad. If the thermostat had partially closed is it possible that the by-passed water would be hot enough to trigger the otter switch?

[gruffalo]

I the otter switch on the rad on a Griff, if so then not the thermostat.

[Aussie John]

It's a pre-serp with the otter switch in the swirl tank, I replaced the switch 2 years ago and it has been working at 90c, if the fans switched on when the temp gauge reached 90c then I'm assuming the water temp. at the otter was hot; I am puzzled by this, maybe I should bleed the rad. and see if an airlock is there?

[TVR Beaver]

same thing if its on the swirl pot or rad (I think)... once the stat closes it keeps it within the engine to warm it up instead of letting it go around the cooling system... if the fans came on it's all hot?.. may sound a silly question but how do you know the fans were on?... not sure I could hear mine at 70mph?

Is the level correct in the fill tank now its all cooled down or have you lost any coolant?

[TVR Beaver]

Aussie John said:

I changed the coolant today but after removing the lower rad hose and undoing the bleed bolt on the rad I only needed about 6 litres to refill, book says 11-12 litres, what is going on? cheers, John.

Mmmmm.. this is interesting... how much running have you done since you did this?.. could it be air-locked or a big bubble??

[Oldred_V8S]

I find after having drained the system it takes a couple of weeks for the car to burp every last bit of air out and for tthings to settle down to normal . It sounds like you had some air in the system still.

[Aussie John]

Hi John, when I saw the temp. go up I opened the bonnet and fans were on. A good call about my coolant change, I've probably done 600 miles since, the car hasn't used any coolant but could have been burping the last of the air.

[TVR Beaver]

Could be... my fans are quick to come on, but the flow on a cool day on the motorway can result in them running too cold if anything (and you have a 75 deg stat in)... could be air collecting in the pump so no movement for a bit although if the air has now gone, your level should have dropped?

when you did the change you say the car was facing down hill... is this true on re-fill also... as I tend to do mine facing up hill to get the last bits out of the heads etc....?....

but as said above.. air coming out should result on a level drop.?.

How did you re-fill the system?.. through the bottle?.. if so the small pipe is obviously open (they can block easy and show a constant level when it's atualy all over the place in the engine)... is the pipe working okey?

I always take the heater pipes off.. fill that... the blead in the head (screw in pipe).. and the rad... all of them a few times to make sure its all gone... I've never had issues with air trapped but I know a lot do?...

Strange one... see how it goes

[Aussie John]

I managed to bleed a bit of air out of the rad so I guess we will see how it goes, thanks to all on the forum for the advice, what a great bunch of blokes.

[carsy]

Has to be air or maybe dirt of some sort that momentarily blocked water flow somewhere. If there is dirt going round though i would have thought you`d have seen the same problem again over a long journey, so my bet is an air lock.

Out of interest what level do you keep the coolant in the swirl pot. ( being a pre serp ).

[Aussie John]

Hi Ian, it runs at about 2/3rds full when cold, never needs a top-up, I wonder if the rad. bleed plug could suck in air but not blow water out.

[carsy]

When cold my coolant is just level with the bottom of the inlet tube from the thermostat. So quite a bit higher than yours. It never throws water out at this level either.

[TVR Beaver]

Oooops.. pre-serp... so forget the small pipe comments

[stevesprint]

carsy said:

When cold my coolant is just level with the bottom of the inlet tube from the thermostat. So quite a bit higher than yours. It never throws water out at this level either.

Ditto.

While re-filling I disconnect the small 5/16 hose near injector 1 to allow the trapped air to escape, as I'm impatient I also blow in the top of the swirl pot which soon pushes the trapped air out of the engine via the disconnect 5/16 hose.

[Aussie John]

I pulled the thermostat to day and did a rough check in a pan of water; opened just before the water boiled. I have ordered a new thermostat in just case.