Cracked block? Symptoms, solutions

[Paul Kelley]

It's me again. Following my recent thread re suspected blown head/inlet gasket, and what seemed to be the answer in a small leak from the radiator and 'condensation' at the oil cap, my mechanic is now seriously considering the possibility of cracks in the block, possibly disturbed by the rebore (to +40 thou). After extensive pressure testing and other checks, it seems increasingly unlikely it is the head or inlet gaskets. Likewise the block-to-head surface was checked and in order. The symptoms are loss of water from the header tank (about a pint again in only a few miles), very creamy oil at the cap, now signs of sump oil discolouring and also the level is above the maximum by quite a bit. No external water leakage is evident anywhere, including in the Vee. The header tank is not being excessively pressurised and the car runs really well and starts first time, although I am not using it now of course.

If it is the block leaking water, are there any known sealant products that offer a permanent seal? The standard ones seem to be just temporary fixes for blown gaskets. My mechanic has used a heavy duty ironised product before, sourced from Fondera engineering (specialists in engine remanufacturing machinery and products). Anyone with any experience of successful engine block sealant products? The alternative is almost inconceivable, especially having had the engine completely rebuilt. Should the cylinders have been resleeved perhaps? It wasn't even suggested and not sure it's a viable option. Cracked and leaking cast iron blocks does seem to happen, I suppose it's a form of metal fatigue after time.

One final thought is the the water pump. My mechanic is sure it's not that but is there anything he should be checking anyway? As ever, thoughts and feedback welcome. Thanks.

Paul

[LD334]

A leaking water pump usually shows as water in the V from the slot in the pump housing. The slot is there to tell you that the top pump seal has gone. It sounds as if both seals may have failed and coolant is passing from the header almost directly to the sump. I would get the pump out and fit new seals.
Pressure testing the block shouldn’t cause it to crack, the pressure in the cylinder on the firing stroke will be way higher than that used in a pressure test. Also, cracks in cast iron are usually fairly obvious. To check, get some flourescein (Amazon sell it) put some in the coolant, remove the thermostat and run the engine for a minute to mix then use a radiator test kit to add pressure to the cooling system and any leaks will become obvious.

[Paul Kelley]

Thanks, will check the water pump further. Didn't mean the pressure testing had caused the cast iron to crack, just the way it is worded! Thanks also for the flourescein tip.

[wilf]

Not seen many (in fact, none) instances of cracked blocks in my time on this forum, so I suspect the water pump seal;s (which can indeed let water into the oil) are a better diagnosis. Fingers crossed for you.

[flying farmer]

I have found that most radiator sealants will stop water escaping from the cooling system wherever it is escaping from, except the water pump seal is that is constantly in motion.

Radiator sealants don't work to stop cooling system pressurisation as the pressure is going to blow the sealant out of the gap rather than force it in.

When in doubt I always lob in a bottle of radweld or K seal and see if the problem goes away before I spend time and money trying to fix the problem. If that fails it is time to investigate further.

Neil

[jbuckl]

Deleted.

[Paul Kelley]

Thanks Neil and Wilf. I've ordered a new (six vane) water pump anyway as I don't know how old my current one might be, so will see what that does. Just googling around (I know, can be dangerous!) there is a surprising amount of instances of both cast iron and alloy blocks becoming porous, including the Rover/Buick V8 as well as our TV8s. There are proprietary products on the market such as Silver Seal Heavy Duty Ironised head and block seal that I'll go to if the new pump doesn't solve it.

I talked to Paul at Stag Classics in Alton (he's a nice and helpful guy always) and he says change the water pump (given the symptoms) but he has says it is not unknown for rebored blocks to disturb a rust spot close to the water jacket. I suppose we have to recognise that water has been circulating around the channels in our iron blocks for around 50 years now. Anyway, I'm keeping optimistic that the pump or the block seal will sort it without having to contemplate the Armageddon scenario. If that did come about it seems that cylinder liners are an alternative to re-boring. Not even thinking about that right now!

Paul

[RNF]

You could always go to a belt driven or electric water pump and be done with the original water pump.

[Paul Kelley]

Well, one for the future maybe RNF. Thanks for the idea.

[RNF]

Also you can check compression as usually cracks in the block happen near the deck of the block (mating surface with the cylinder head).

Is the engine smoking? if so what color smoke?

You can get one of these block testers. They're pretty cheap.

John

[Paul Kelley]

Thanks again John, useful tips re compression testing and block tester. I would say I am missing a couple of the tell-tale head gasket symptoms: no noticeable excess pressure build-up in the cooling system and no white smoke. Plus the head gaskets were renewed as part of the rebuild. Hence suspicion is on the water pump, so we're changing that first anyways and see what it does. I'll post an update. Paul