Coolant/unburnt fuel leaking from head gasket

[Charles73]

So the engine has been back in the car for a while now (around 500 miles) after a rebuild, including overhauled head, and has just been for its first tune since the rebuild. Before tuning, it was running rich and I had unburnt fuel leaking out of the manifold, mostly on no.3. The tuner also informed me the ignition timing was out (pinking) which he also corrected.

After an hour or so of fairly 'spirited' driving over the weekend, I noticed I'm still getting the black unburnt fuel leaking from the manifold on no.3, but this time there is coolant leaking from the head gasket in that area too. I noticed a couple of spots of coolant on the floor just prior to tuning and just put it down to overspill when I checked the levels.

It's also may be worth mentioning that it initially was not firing on no.3 after starting it the morning after the drive, bearing in mind it was running absolutely fine when I parked it. So I checked ignition, plugs, carbs and found nothing suspect. It eventually was firing and running absolutely fine after a little while...

Maybe this suggests a coolant leak is preventing no.3 from firing properly, especially when cold, hence the unburnt fuel? There is no sign of oil in the coolant at the moment, and I'm confident my tuner resolved any running rich.

The block was skimmed, and rebored to suit new pistons. Ajusa gasket fitted, torqued to 65 ft.lb then retorqued recently. As I say, the head was overhauled by a reputable TC man, including refacing.

Do you have any suggestions on what the cause of this could be, or anything I should check? This is very frustrating, as I've just got her oil tight and running beautifully!


Many thanks

Charles

[HCA]

You need to strip it down and investigate! If you have liquid leaking, then it can only be gasket, badly machined faces or poor assembly.

I am not sure what else you want to hear?

[nmauduit]

It sure would be a pain if a water leak remained after a good overhaul... are you sure that the observed coolant on the floor is not coming from somewhere else than the head gasket (and that it is indeed coolant)? after a good overhaul I suppose the usual sources of gasket leaks (water passage corrosion... which can develop "one way" tiny leaks initially, as pressure increases when the coolant is hot then can seep in, likewise combustion pressure) were checked, and it is possible that a crack has remained undetected... though not very likely (if coolant prevents a cylinder to run you'll see it at the exhaust with white smoke) : I would take some time observing to track and confirm the point of origin of the leak if possible (also, if the sparks have been sooted by rich combustion for a while, make sure they are all cleaned up or change dubious ones to rule out combustion issues). Then you may also try to put the cooling circuit under pressure (within reason) or the #3 chamber as in a leak-down test for static observations after cleaning the suspected area... good luck !

[alanr]

As other have said if you have coolant leaking then there is no alternative but to strip and investigate!..Coolant is either leaking or it is not..simples really!
Either it is poor machining, misaligned head gasket,wrong size gasket for bore size or could even be a cracked/porous cylinder head or block.
None of it is good news and it is gut wrenching to find such a problem so soon after a rebuild, but from the way you describe the symptoms you have no alternative but to get stuck in again!

Good luck and keep us posted with what you find!

Alan

[Charles73]

I'm quite confident that both surfaces were machined correctly and that they were assembled correctly...

I can only guess its a cracked block or head. Will this mean that the component in question is scrap?

Thanks

[alanr]

Not necessarily scrap at all. It just depends on where the leak is coming from.
Finding where exactly the coolant is escaping from is your main challenge. It may only be leaking at high temperatures which may take tracking it down difficult.
If you are absolutely sure it is leaking coolant from the cylinder head/block your first step is to take the head off and get it pressure tested by a company that knows exactly what they are doing.

Alan.

[tdskip]

Ouch, sorry to hear of your trouble here. Would agree that there is not much to do but to open it up.

Keep us posted and fingers crossed.

[EPA]

Seems unlikely but have you checked that your water leak isn’t coming from the core plug situated in that area?
Best of luck
Ed

[david.g.chapman]

I would try to make absolutely sure that coolant is not leaking anywhere else than the head gasket before starting any stripdown.

I would do the following:

1. Dry and clean the engine around the head gasket, all the heater and coolant hose joints - anywhere where coolant can get out. Note that a leak at either end of the upper heater hose can end up under or near the sump.

2. Get a bright torch, start and run the engine up to temperature so that the cooling system is pressurised.

3. Look very carefully around the coolant joints and at the head gasket. Feel under the hose joints as leaks can hide and track down the engine metalwork.

4. Pray to the Lotus gods and hopefully you will see it coming from somewhere easy to fix.

Best of luck

Dave Chapman.

[mbell]

I too would do a few checks before stripping down. I'd do as Dave suggested, likely a also do a coolant system pressure test (engine not running but hot), as might be able to see where the leak is.

I'd also do an exhaust gas test on the cooling system. This will give you some clues for what kind of issue your looking for on strip down. Is it just coolant leak or is there a combustion leak as well?

[ncm]

"The block was skimmed, and rebored to suit new pistons. Ajusa gasket fitted, torqued to 65 ft.lb then retorqued recently. As I say, the head was overhauled by a reputable TC man, including refacing"



If you do lift the head then I would check that the head bolts are clamping the head and not bottoming out in the block.

Brian.

[Charles73]

Thanks for all of your comments gents.

After further inspection, I decided to go ahead and removed the head. The coolant was certainly coming from the head gasket. Gasket was seated correctly. All cylinders seem to be firing evenly/same amount of carbon build up.

I carefully removed head gasket. No immediately obvious signs of failure.

There is no obvious crack in the block, where I was expecting to see a crack in-between the water way and no.3 cylinder. I'm yet to inspect using a magnifying glass.

I think if I find no cracks, I'll check the bolts weren't bottoming out. I plan to replace the bolts, maybe with stud/nut setup.

So far so good...but with no obvious causes I'm a bit confused! I'll report back once I've completed a more thorough inspection.


Charles

[nmauduit]

I think if I find no cracks, I'll check the bolts weren't bottoming out. I plan to replace the bolts, maybe with stud/nut setup.

studs are a bit pricey but well worth the expense imho... there would be dies one can use to enhance small cracks, but the bottoming or poor clamping of some bolts (were they new? of the thin waist type? with suitable washer where appropriate? risk of something partially filling one of the bores?...) sounds like a promising and optimistic lead... good luck !

[Mazzini]

I see that the block has been faced. Do you know how much material was removed? Is there still a step up from the front cover to the block?

Edit: a 25 thou step is about right.

[gjz30075]

Check the block and head mating surfaces with a straight edge. Or, take the head back to the machinist
for a good double check.