losing coolant from reservoir overflow

[playmonkey]

Well, it was all going so well.

I've just changed the engine in my MK1a with a MK1b engine and it fired up straight away.

I have just filled it with coolant and bled the system. I let it run for about five minutes, tickover is smooth, temp gauge sitting in the middle.

Then I noticed a puddle of coolant under the back of the car. It is coming from the reservoir overflow pipe. I tried another rad cap but done the same thing.

It's only ticking over and not getting hot but the system is obviously pressurising - I think? Head gasket? Surely I can't be that unlucky....

Any thoughts before I throw my toys out of the proverbial....

Thanks

[Lauren]

Make sure the valve is connected right on the expansion tank and not the wrong way round.

Bleeding is a PITA on these cars, always seemed to take me around 40 minutes with all the tubes on the bleed valves cable tied up the bonnet. Look at the BGB to ensure you get all the bleed valves and get it right up to temp.

It sounds like you still have air in the system.

[playmonkey]

Hi Lauren

Thanks for the reply. Makes me feel a little bit better as I'm sure the engine is ok.

I do have it slightly easier because it is a race car and the heater system has been taken out - one less valve and 5 litres less coolant to buy

The expansion tank and hose connections were left from the previous engine so I don't think that's the problem but I will check. Didn't have this problem before.

You could be right about the air though as I didn't have a hose to fit on the radiator to bleed and could only open the valve and fill until the coolant came out and it definitely is below the filler cap. I suppose I could jack the car up at the front? Would that work?

I am thinking that maybe the gap between the valve and the top of the radiator would still be an air pocket so yes, might be air. Why would this cause it to push water out of the overflow? The expansion tank was filled to max and it moved a bit lower on startup.

I followed the bleed recipe from this forum but not to the letter so will have to try harder 6/10.

Thanks

[PW@Woodsport]

It could just be bypassing a worn out pressure cap, no coolant should be getting past the pressure cap (not to be confused with the expansion bottle cap) when the engine is running, that is either a symptom of 0.9bar exceeded in the cooling system or a faulty cap.

Replace the pressure cap first, if coolant is still getting past the cap then you either have a ton of air in the system or it is pressurizing up past 0.9bar which could be head gasket.

Also check the bleed screw O rings on the thermostat housing, coolant could be getting pushed into the expansion bottle there too.

[playmonkey]

I was using a 1.5bar cap from the previous set up when I noticed the leakage, I then tried the old .9bar cap and it still pushing out fluid - so two faulty caps would be unlucky, especially as it was dry with the old installations...but not to be discounted.

I'm interested to know why would a ton of air in the system would cause it to leak from the overflow?
The O ring theory is interesting and easy to check - I can just remove the hose from the expansion bottle and see if fluid comes out when it's running although wouldn't that just fill up the expansion bottle?

Questions questions....

Thanks

[PW@Woodsport]

I agree, two caps both allowing coolant past would be very unlucky, so if it is bypassing the cap it is doing so at more than 1.5bar pressure.

Air in the system causes steam, which raises the pressure beyond the cap rating.

If there was that much air I would also expect you to have a bouncing idle as the waxstat cold idle valve would be stuck open for too long.... so that kind of rules airlocking out.

There is a definitive head gasket test I use which is 100% guaranteed to diagnose failure. It consists of a hollowed out spark plug welded to a tube, which is then welded to an air line fitting. I pressurize each cylinder in turn to 60psi at TDC with the pressure cap removed. If any bubbles come up then the only place they can do so is at the head gasket. You can also use a leakdown tester kit instead of making your own tool.

Check the thermostat bleed O rings.

[Lauren]

The trouble is, you need those bleed screws open in the front with the hoses connected whilst the engine is running. They're normally in the front boot somewhere if your car still has them. They're clear hoses that connect on and you hang them off the bonnet strut. That way you can be sure to get the air out properly.

The air will expand which pressurises the system.

In all honesty it is many years indeed since I've had the pleasure of bleeding an AW11 system. I wish it was like my AE86 which sorts itself out, but it would with a front engine and radiator!

If there is air in the system it does tend make the idle fluctuate.

[playmonkey]

Just been down to the car and how happy I was to see a pool of coolant and dripping from the overflow pipe...

Spot on with the thermostat bleed O rings - it was still letting fluid out whilst tight and the gravity must be siphoning straight out of the overflow.

Joy upon joy

As for the bleeding, the whole car has been stripped out so don't have a bleed hose. I'll go and buy a length of clear. I'll read the instructions again but I'm sure it doesn't say that the engine should be running whilst bleeding at the rad... but....

It was idling smoothly so I don't think there was much air left, however I'll do it again.

I checked the bleed screw on the other engine and they had blanked it off.

So, O rings? Or is there a mod?

Cheers, and thanks

[PW@Woodsport]

You're welcome, just get a new bleed complete with O rings from Toyota, part number 90910-09093