Coolant Leak

[Malsprint]

I am trying to locate a coolant leak. I loaned a pressure testing pump/gauge from autozone (US) and pressurized the expansion tank to 13psi. It appeared that I had a leak at multiple points on the inlet side of the cylinder head. There where also leaks from the thermostat housing tube connections. To test if the thermostat leaks were running along the cylinder head joint I jacked up the car so that the cylinder head was sloping forward. I was surprised how much I had to jack up the car and this is with the help of the slop on the garage floor.

[Malsprint]

At this angle there was no evidence of any leak along the cylinder head joint so it does look like the water was running along the joint and pooling on top of the block. However there is a definite pool between the cylinder head and the water pump. Its very difficult to see in that area. This could be the cylinder head or hopefully the water pump gasket.

I plan to remove the inlet manifold to gain access and get a better look. Once I have the manifold off is there anyway to test the cylinder head joint.

[xvivalve]

The usual culprit is the bypass tube between underside of inlet manifold and top of water pump cover; the fan then blows the coolant along the joint between block and head and it pools in the core plug. It would be unusual (in my experience, at least) for the water jacket to compromise at head gasket and exhibit externally along the joint.

[cleverusername]

At this angle there was no evidence of any leak along the cylinder head joint so it does look like the water was running along the joint and pooling on top of the block. However there is a definite pool between the cylinder head and the water pump. Its very difficult to see in that area. This could be the cylinder head or hopefully the water pump gasket.

I plan to remove the inlet manifold to gain access and get a better look. Once I have the manifold off is there anyway to test the cylinder head joint.

I had a similar issue and could only stop the leak by getting the inlet manifold skimmed flat. If it isn't flat it will never seal properly.

[Malsprint]

Is it possible to remove the connecting tube through the thermostat housing. The manual shows that it is inserted this way but I guess it will be difficult the grip the tube via the thermostat housing in order to remove it. If this is easy to do then I would probably try that first.

Or should I just remove the manifold.

Taking the manifold off would have the added benefit of allowing me to determine if its flat and needs machining.

[xvivalve]

There is a very slight step machined into the inlet manifold against which the O ring seals. I always place the bypass tube into the water pump cover before fitting the manifold as I feel this provides a far more positive seal.

If you had some sort of narrow puller you might succeed in pulling the tube up through the manifold, but I don't think it would easily seal again afterwards if re-used

[Carledo]

The subject of the bypass tube has been comprehensively covered recently in the "Project PFJ is baaack!" thread in the resto section.

Turns out that pre 74, the tube can only be removed by taking the manifold off, after that it could be removed upward through the stat housing as shown in the manual. There was also an early tube design that, like the factory plug tubes, was rubber sheathed steel and therefore "one time use only". This tube is NLA and the modern ones with separate O rings are the norm.

I'm normally reluctant to remove the manifold if I don't HAVE to (it's a pig to seal the water gallery as has been said) and have used various methods to pull the tube out, most successful has been an old thread tap that just about grips inside the tube, pulled up with a mole grip.

But in your case I highly suspect that the manifold gasket is leaking around the water gallery which is directly above the pump housing and a leak here can often be mistaken for a bypass tube leak. In your shoes, i'd replace both the manifold gasket AND the bypass O rings for a clean sweep. I also use a bead of Silicone sealer just around the water gallery area of the manifold gasket, then i've not needed to get the manifold skimmed. Of course if the manifold mating face is badly eaten by corrosion (Which I HAVE seen) you'd have to rethink.

Steve

[Malsprint]

I guess the manifold is coming off.
Thanks all.

I will keep you posted.

[yorkshire_spam]

Not sure if it's relevant here, but in my experience the inlet manifold gaskets currently supplied are WAY too thick - meaning that the o-ring on the inlet manifold doesn't seal correctly (I'm talking about my own experience on an 1850, so as I say, may not be relevant)
1.65mm (uncompressed) for new vs 0.55mm for NOS gaskets.
I appreciate that the new ones are a different material and might compress more once fitted, but they made getting the manifold o-ring to seal pretty much impossible.

[RSi]

Lovely car BTW

[USSprinter]

Not sure if it's relevant here, but in my experience the inlet manifold gaskets currently supplied are WAY too thick - meaning that the o-ring on the inlet manifold doesn't seal correctly (I'm talking about my own experience on an 1850, so as I say, may not be relevant)
1.65mm (uncompressed) for new vs 0.55mm for NOS gaskets.
I appreciate that the new ones are a different material and might compress more once fitted, but they made getting the manifold o-ring to seal pretty much impossible.

Interesting point! I instantly noticed when I removed the Sprint’s inlet manifold the difference between the old gasket (thin, flexible, rubbery) and the new (thick, rigid, cardboardery). The new gasket material also has a “3D” aspect: there is a slight circumferential raised ridge in the gasket material surrounding each bolt and port opening. For the Sprint that might help better seal each opening in the single integral gasket piece (once it is fully compressed), but I can certainly see the issue for the 1850 with its separate single o-ring for the coolant port. Fingers crossed for the Sprint when I finally install all the new hoses, fill up the antifreeze, and crank ‘er up.

[cleverusername]

The subject of the bypass tube has been comprehensively covered recently in the "Project PFJ is baaack!" thread in the resto section.

Turns out that pre 74, the tube can only be removed by taking the manifold off, after that it could be removed upward through the stat housing as shown in the manual. There was also an early tube design that, like the factory plug tubes, was rubber sheathed steel and therefore "one time use only". This tube is NLA and the modern ones with separate O rings are the norm.

I'm normally reluctant to remove the manifold if I don't HAVE to (it's a pig to seal the water gallery as has been said) and have used various methods to pull the tube out, most successful has been an old thread tap that just about grips inside the tube, pulled up with a mole grip.

But in your case I highly suspect that the manifold gasket is leaking around the water gallery which is directly above the pump housing and a leak here can often be mistaken for a bypass tube leak. In your shoes, i'd replace both the manifold gasket AND the bypass O rings for a clean sweep. I also use a bead of Silicone sealer just around the water gallery area of the manifold gasket, then i've not needed to get the manifold skimmed. Of course if the manifold mating face is badly eaten by corrosion (Which I HAVE seen) you'd have to rethink.

Steve

Tried silicon sealant and it didn't cure the issue. Once I had it skimmed it sealed without any sealant.

It is a rubbish design, the way the bolts are arranged means there is no clamping force at the bottom of water gallery, which is were it seems to leak.

[Malsprint]

This looks like it could be the source of the leak.

Any advice on the best gasket to use and where to get it.

The manifold appears to be flat when inspecting with a straight edge. Hopefully I can get it to seal without skimming it. Plan B.

[soe8m]

Any advice on the best gasket to use and where to get it.

NOS on ebay, a payen nos set or make one yourself from decent gasket paper.

The current grey newspaperpaper ones that every classic sellers do sell are useless.

Jeroen

[cleverusername]

This looks like it could be the source of the leak.

Any advice on the best gasket to use and where to get it.

The manifold appears to be flat when inspecting with a straight edge. Hopefully I can get it to seal without skimming it. Plan B.

Exactly were mine leaked and I tried a variety of different gaskets and sealants with no success. I hope I am wrong but the only thing that cured it was getting the manifold skimmed.