Rising and Falling of Coolant Temp

[gizzardio]

Hi All

Coming back from Silverstone classic yesterday. All is well until I notice coolant temp rising towards 100degC at a steady 70mph without having previous ragged it or sat in traffic. Normally it sits about 87degC just under the white mark at 90degC.

Then after a few miles more, it came down so I thought great, just a strange quirk. But then it bounced right back up to near 100 again, then a few more miles dropped and repeat.

Pulled off at services, coolant had definitely left the cap on the swirl pot as it was dried on underside of bonnet and all down the pot itself. After cooling down for while, I take cap off and surprised to see almost full coolant, and expansion tank is also at OK level. Thinking maybe its misleading, I run engine with cap off and rad bleed valve open to burp it in case of air lock and loads off coolant starts tipping out after a few mins. So it may have been air in there so I keep topping up after it flows over until it eventually stops flowing over and I can see coolant level is fine just an inch below swirl pot top.

I also get coolant fan sensor switch spades and short them so fan is on permanently just as extra precaution to get me home. All way home the temp never gets above 90 which is good, but it keeps fluctating up and down all the way quite wildly. Its 90 then falls to say 80 for a few mins, then shoots up to 90 again then repeat.

Any thoughts? Is my swirl pot pressure cap had it? Anyone else had these weird symptoms?

[Niiige]

I had the same symptoms in the spring.

I checked my coolant levels - slightly low. But only slightly.

Fan came on as required - so it wasn't that.

Swirl pot valve cap had perished - so got a new one.

I was worried about my radiator - looked okay, but popped Radweld in just in case.

Checked all pipes for possible leakes.

Got a really strong cup of tea.

Followed the topping up of coolant/burping procedure from Steve Heaths bible - both methods.

Been right as rain since - and has been all around Europe.

[gizzardio]

Hi

Thanks, so I suppose all I can try that I haven't already done is to replace my pressure cap and more burping if its a really stubborn air lock. The V8 has a top hose which is actually higher than the swirl pot top and is upside down U shape so a perfect design for trapping air in this. It did get pretty hard to squeeze when running at working temp though so lots of water was getting through it.

Anyone recommend the pressure cap for the swirl pot I need?

[Niiige]

I got mine form the TVR Parts website - but be warned their delivery costs are high unless you order several items

That said - I'm sure Philpott will be along shortly with a clicky thing......

[greyhulk]

gizzardio said:

Hi

Thanks, so I suppose all I can try that I haven't already done is to replace my pressure cap and more burping if its a really stubborn air lock. The V8 has a top hose which is actually higher than the swirl pot top and is upside down U shape so a perfect design for trapping air in this. It did get pretty hard to squeeze when running at working temp though so lots of water was getting through it.

Anyone recommend the pressure cap for the swirl pot I need?

15lbs long reach from what ive read before on here *awaits swirl pot/expansion tank cap discussion again *

[gizzardio]

Thanks. I'll take a look.

I'm leaving my arrangement as it is as its absolutely fine up til now so no need to resurrect that discussion topic..

[greyhulk]

this time last year it was me with the overheating issues! The culprit was a blockage in the rad which a recore solved

[gizzardio]

Hope its not that. I just got it re-cored in Jan!

[Rockettvr]

Just had this problem on my wedge - turned out to be an intermittent/failing thermostat.

[v8s4me]

Rockettvr said:

Just had this problem on my wedge - turned out to be an intermittent/failing thermostat.

Good shout. Also try a complete flush of the system. If that's never been done then there will be a lot of crap in the system which won't be helping.

[gizzardio]

It was flushed and refilled when I had the rad re-cored in Jan so I hope its nothing to do with that so soon.

I will purchase a new thermostat anyway and fit it for the sake of 15quid.

Any thoughts on the lower temp opening ones against the higher? 82degC v 74degC are the ones I've seen on racetech.

[v8s4me]

gizzardio said:

...I will purchase a new thermostat anyway and fit it for the sake of 15quid. ....

Why not run it without a thermostat for a few miles and see if the problem goes away. That way you'll know one way or the other if you have a faulty unit.

[phillpot]

I was told many years ago, by some one who's opinions I highly respected, that if you remove the thermostat (eg in a race engine) you should fit a restrictor plate, a disc of metal with a few holes in, as the system/pump needs a degree of restriction to pump against?

[GreenV8S]

I don't recommend running without a stat. It prolongs the warmup time, which is bad for the engine, and means the engine temperature will be constantly fluctuating as the speed and load change. That will significantly increase the strain on gaskets and seals.

[Craig Brown Photographer]

So the White line is the 90 degree mark? Not when the need needle sits at horizontal?

[magpies]

phillpot said:

I was told many years ago, by some one who's opinions I highly respected, that if you remove the thermostat (eg in a race engine) you should fit a restrictor plate, a disc of metal with a few holes in, as the system/pump needs a degree of restriction to pump against?

that's what I've been told too


my S ran with the needle horizontal most of the time 'til I went to Burghly in the frost and the needle stayed well below horizontal (came up to horizontal when I tailgaited a bus for a few minutes then dropped down when I backed away). I thought the thermostat was stuck open so when home I removed the housing only to find no thermostat - just the outer ring acting as a restrictor - the centre mechanism having been removed b y a previous owner.

[gizzardio]

Hi

So I removed my thermostat tonight and am I right in thinking that if I drop it in a jug of boiler water it should just open up?

I did that and nothing happened. But it must have been working before otherwise my engine would have just overheated, rather than just fluctuate.

Unless I've got this wrong...

[Top Gear TVR]

My experience tells me start with the correct sealing and functioning of the swirl pot cap.

[magpies]

The thermostat will open before the water boils.

[gizzardio]

Top gear - yep I've now bought a new cap and seal and will stick that on.

I was more curious than anything else to check the stat out and see it working.

Very weird then that nothing happens when sat in pan of boiling water.