Rover v8 dumping coolant

[dhennings]

I am recommissioning a rover v8 engined LR roadster cobra. I have fixed all the problems except one. The engine is fine when blasting along but at tickover the levels of coolant soon rises in the exspansion tank and then it pushes out the coolant. However when it does this the coollant is not at boiling point - more like about 70c. It seems like an airlock is forming - I have tried bleeding the system at the highest point and there does seem to be air in it before it happens. The pump appears to be circulating ok - when you take a hose off it sqirts suggesting the pump is ok.

When the coolant is rising if you give ita good rev you can see the level in the tank drop about a half inch and then it rises back again as the revs fall - I assume that also shows the pump is working

I cannt work out why it is doing it or where the air is getting in from. I am going to do the test on exhuast gases in the water but if it was that it would surely be worse at high speed?

If the cap on the surge tank was faulty would that do it? Could the pump still be faulty?

Any ideas gratefully recieved

[wilf]

If you leave it alone and ticking over, does it continue to puke until all the fluid has gone? Or does it stop once a somewhat lower (but possibly still OK ) level has been reached?

Probably worth changing the pressure cap anyway - they can fail.

[Big Thirsty]

Originally Posted by dhennings

I am recommissioning a rover v8 engined LR roadster cobra. I have fixed all the problems except one. The engine is fine when blasting along but at tickover the levels of coolant soon rises in the exspansion tank and then it pushes out the coolant. However when it does this the coollant is not at boiling point - more like about 70c. It seems like an airlock is forming - I have tried bleeding the system at the highest point and there does seem to be air in it before it happens. The pump appears to be circulating ok - when you take a hose off it sqirts suggesting the pump is ok.

When the coolant is rising if you give ita good rev you can see the level in the tank drop about a half inch and then it rises back again as the revs fall - I assume that also shows the pump is working

I cannt work out why it is doing it or where the air is getting in from. I am going to do the test on exhuast gases in the water but if it was that it would surely be worse at high speed?

If the cap on the surge tank was faulty would that do it? Could the pump still be faulty?

Any ideas gratefully recieved

Hello,

Can you tell us the capacity of the engine ??

[dhennings]

If i leave it ticking over the coolant does stop coming once the exspansion/header tank is completely empty - at this point the bleed valve on the top hose only lets out steam which makes it seem a huge air bubble has formed and therefore? the top of the engine is not getting any water circulation.

[dhennings]

rover 3.5 - orginally from an SDi

[KevinW]

assuming header tank is at the highest point in the system, try jacking the car up to excentuate this, then start engine and run till its hot (ie fans cutting in intermittently), then rev it up to about 4-5000 revs and hold for 10 seconds with the cap off. you should see the level rise. eventually it will spew out, and produce a plume of steam as it evaporates on the hot parts of your engine bay. try this several times, topping up each time. eventually the air lock will clear itself, assuming you havent got a leak somewhere, and it will find its own natuarl level in the system.

- based on my own experience and advise gained from others trying to get air out from an SD1 RV8 in a Sumo.

just a thought - is your header tank one with a single inlet at the bottom, or does it have tow inlets (one at top, and one at bottom)? - mine has the latter.

[dhennings]

the tank has one inlet at the bottom and the outlet at the top for when the cap releases pressure. is the other one better and if so how are both pipes plumbed into the system

[Sidecarbod]

Originally Posted by dhennings

I am recommissioning a rover v8 engined LR roadster cobra. I have fixed all the problems except one. The engine is fine when blasting along but at tickover the levels of coolant soon rises in the exspansion tank and then it pushes out the coolant. However when it does this the coollant is not at boiling point - more like about 70c. It seems like an airlock is forming - I have tried bleeding the system at the highest point and there does seem to be air in it before it happens. The pump appears to be circulating ok - when you take a hose off it sqirts suggesting the pump is ok.

Originally Posted by dhennings

When the coolant is rising if you give ita good rev you can see the level in the tank drop about a half inch and then it rises back again as the revs fall - I assume that also shows the pump is working

I cannt work out why it is doing it or where the air is getting in from. I am going to do the test on exhuast gases in the water but if it was that it would surely be worse at high speed?

If the cap on the surge tank was faulty would that do it? Could the pump still be faulty?

Any ideas gratefully recieved

The top hose is the usual cultrate for airlocks, you need to make sure that it is as straight and low as possible.

Your manifold may also be a problem depending on what type it is. The Edelbrock performer has a problem in that it can shield the thermostat from the hot coolant to the point where it does not open at the right time. If you have an Eddy manifold let us know so we can explain the simple fix. (Cue Graham and his wiki!)

Some header tanks have a filler neck that is too long, this totally messes up the blow off pressure of the rad cap, again this can be sorted.

Some thermostats don’t have any bleed holes, a lot of air can get stuck behind them. If yours does not have a hole then you can drill a 3mm hole in it. I would also run a 74 degree stat if I was you. (Assuming that you’re not running EFI). The engine will then run at about 80 odd degrees which is fine for an RV8

Like Kevin said some info on the design of the header tank would be useful. Basically the term “header” is often used when the tank is really an expansion tank, it all depends on how it’s plumbed in. For example the pilgrim setup uses an actual header tank and that is prone to problems due the size and location of the air bleed at the top.

I bleed my system by running the engine with the header tank cap off, I rev the engine whilst standing next to the tank with a supply of coolant, the level in the tank will drop as the air escapes out of the system via the open top of the header. Each time it drops I refill the tank to about 2/3rds full. When the level does not drop anymore I fit the cap back on and go for a drive. When the car is back in the garage I let it cool down then re-check the level, if it’s not at 2/3rds I top it up again. After that it won’t need any more coolant.

HTH,

Pete

[Sidecarbod]

Originally Posted by dhennings

the tank has one inlet at the bottom and the outlet at the top for when the cap releases pressure. is the other one better and if so how are both pipes plumbed into the system

You just posted as i was posting so I did not see your reply above!

Basically you have an pressurized expansion tank, it needs to be mounted higher than the rad. As the water in the rad heats up it will expand into this tank, it will force out the air in the tank via the blow off valve in the cap. (Check that it is a spring loaded blow off cap, not just a plain cap). When the engine is stopped and it cools down a vacuum is formed that will suck the coolent back into the rad. The little disk valve in the bottom of the cap will allow the air back into the expansion tank.

with this setup you do not really want much coolant in the tank when the engine is cold, if you over fill it it will just get blown out when the engine heats up!

My money is on a big nasty air lock somewhere!

Where does the pipe that connect to the bottom of the expansion tank connect to the rad? if its at a low point then it will be very hard to get the air out of the system. if its at a high point then the air can self bleed to a degree.

Pete

[Sidecarbod]

Originally Posted by dhennings

the tank has one inlet at the bottom and the outlet at the top for when the cap releases pressure. is the other one better and if so how are both pipes plumbed into the system

Both systems can be made to work.

The header tank system requires that the radiator has a small take off point high up to allow the air to escape. This is a drawback as some coolant will also take this route and thus bypass the rad.
It also requires a low take off point the the tank uses to keep the system topped up.

I'd stick with what you've got for the moment until you have exhausted all the possible solutions.

Pete