The V8 Owners Forum -

On my first run out (see 'Have I missed Summe'r post) the temp gauge went very high at 120+. It may be the gauge / sender reading and need to check with laptop using a calibrated sender but I probably still have air in circuit.

Stupid question but how / where do I fill up the system?

I have the standard TVR swirlpot whose top is about the same height as the radiator top. I have a standard TVR header tank with blue (VW) cap. I also have a top-up plug at the top of the radiator. Finally the top hose is above radiator top so will have air in it as are the heater hoses. Water does circulate via heater.



As the top of the header tank is just about above the highest heater / top hose level do I:

1. Just ensure swirl pot does not have air in it by topping this up to full.
2. Ensure radiator top is always full of water.
3. Leave header tank half full, empty or nearly full.

If you hook up your laptop running TunerStudio, you can get a readout of the EFI coolant sensor. This may not read exactly the same as the car gauge since the sensors are in different places - but should be quite close, if the car sensor is in the usual place.

Way I use on my SD1 is to fill it up with the engine running, squeezing the top hose to try and burp out any air. When the thermostat opens, fill to the top and replace the cap. Any excess coolant will be expelled as it expands.

My top hose is the highest part of my system. I cut it and put in a short length of aluminium pipe. I then fitted to that a screw in cap and put a bike tyre valve in that. I now fill through the cap, and once the system starts to pressurise I can vent the air by pushing in the valve with an allen key.

Regards,
Dave

Dave 1:
Yes, that's what I plan to do.
Yes but one can't squeeze these pipes, I'm afraid.

Dave 2:
Yes, I should have done something like that.

Real question is should a) swirl pot be normally full (when cold), and b) how full should header tank be when cold?

With systems fitted with an expansion tank, the rad itself would normally be full even when cold. Or rather that's the way I've found it on maker's installations. In other words, they seem to size the expansion tank to allow just this.

Richard,
In the standard TVR set up, the top of the rad is lower than the swirl pot.
Consequently air in the rad would rise up to the pot and then be forced to the header tank as the coolant expands during warm up.

On my Chimaera, I use to fill the swirl pot and half fill the expansion tank.
It would take a couple of warm ups to expel all the air out through the coolant in the header tank and the level in the header tank then need topping up but never let run dry.

I think in your case the top of the rad is likely to trap air so you would need to bleed it as the engine warms up until no more air is escaping.

In the case of your top hose, you may need to introduce a bleed but a good rev may shift any air into the swirl pot and then out through the expansion tank.

Hope this helps,

Regards Denis

Thanks Denis,

Having seen a few other posts seems you're right. I cannot alter the positioning of the swirl pot and header tank but have a bleed valve on top of rad so it seems:

- Swirl pot will trap air in general circuit so can bleed that.
- Bleed plug in rad will allow bleeding of that
- Air in expansion tank can easily be removed when filling to half full.

So given a few attempts, I should solve that issue. Also pump does seem to get water passing through heater circuit so should eventually remove air from here too.

I'll give it a go. Thanks

You will find that air will always accumulate at the highest points. Even when you perfectly bleed it, air will still build up.

Therefore from each highest point you need a small pipe returning to the header tank.

The level in the header tank must be higher than all the other high points.

And the header tank must have enough headroom for expansion to occur without it
overflowing and then dropping below the highest point.

If that can't be achieved, then you need to switch your header tank to an expansion tank (i.e. run it at atmospheric pressure, not system pressure), and run a single pipe from the bottom of the expansion tank to the highest point in the system. The highest point then needs one of those clever radiator caps that allows excess pressure to expel air or water to the expansion tank, and to draw water back from the expansion tank when it cools. Thus it will self prime. This is what I do on my Land Rover as the radiator is at the highest point (touching the bottom of the bonnet), and I can't get a header tank any higher.

Chris.

Some time ago, I bought a coolant system pressure test kit off Ebay - Chinese made, but very nice and a fraction of the cost of pro garage stuff.
Mainly to find an elusive minor leak on my BMW. (With BMW labour rates you can buy quite a few expensive tools and still save money )

Not only did it work for that, it also made filling the BMW very much easier. No need for scalding hot coolant squirting out of bleed valves. Just bleed it cold, but pressurized.

Same applies with my SD1 - it seems to push out any air pockets back into the header tank in one go.

One of those tools you don't how you ever managed without it.

Does your car have a cabin heater in it?
If not are the pipes just linked together? So forming a loop with no water resistance?

If so the water will go engine round heater circuit back to engine without going via a radiator so never loose ant of the heat.

I looped mine together. But inserted a restricted with a 1.5 mm hole in it so that any air will move through and end up in the header tank.

Reduced the big swings in temperature I was seeing on mu gaugeA

ian

ChrisJC wrote: The level in the header tank must be higher than all the other high points.

Chris.

Strangely enough the header tank (If you want to call it that) on a TVR is very low down by the chassis rails. ( It has a normal pressure cap just like Richards ) This expansion tank works in combination with the swirl pot which itself is positioned high up. The theory is that air will find it's way to the swirl pot and this pot has a small bore tube at it's top which feeds into the bottom of the header tank. As the engine heats up, air is displaced via the small bore tube through the coolant in the header tank and out through the pressure cap when the design pressure it reached. On cooling down, only coolant from the header tank is sucked back into the swirl pot, provided the header tank is not dry.

On Richards set up the top of the rad would appear from the photos to be a likely trap for air as air will not want to drop through the rad nor will it be able to return to the swirl pot due to the loop down from the rad.

Bleeding the air out of the rad may work ok but a better solution would be to have a small bore tube connected between the top of the rads and teed into the smal bore tube which currently run between the swirl pot and the header tank.



Regards Denis

The crux of the matter being that the air all collects at the highest point, and has a way to be expelled through a volume of water which will be sucked back in when the engine cools down.

Chris.

Well thanks and Denis's explanation is about it.

To my slight surprise all air seems to have gone out of system by first bleeding / filling the swirl pot so it is full to top. Then bleed / fill rad so it is too. Then fill header / expansion tank half full. As Denis says, air eventually gets from swirl pot to expansion tank via the rubber tube from top of swirl pot to bottom of expansion tank. So now I seem to have an air free system.

BTW, I do have a cabin heater but I also have an H pipe with the H link a small bore so when heater water tap is off, water can by-pass but when on, most water goes via heater.

I've been away for weekend. However I managed to spend a short time and it now seems as though I did not have temp gauges the wrong way around so 90 is about right for water and a relief. The oil went to 120 max within a mile or two from home so it's not the actual oil temp. I seem to have several funnies with wiring and engine will not always start so need to sort out these items. Probably all related to each other but at the moment a needle in a hay stack comes to mind.

Yet more hours before I can really get out on the road!