W163 ML 500 | Cracked block?

[pompeypetey]

I appreciate diagnosing these kinds of things is very difficult over the internet, but I'm wondering if anyone has any bright ideas before I give up on the infernal thing.

Around 7 months ago head gasket failure was diagnosed due to over pressurisation of the cooling system causing coolant to spill out of the expansion tank and the top radiator hose to collapse when left to cool down. CO2 was also detected in the coolant and the system pressurised from cold in around 30 seconds.

The expansion tank cap was replaced, then the expansion tank along with another new cap to no avail.

At this point I bit the bullet and spent the next 6 months replacing the head gaskets, valve gaskets etc. New TTY bolts used throughout. I knew this was a risk because everyone was telling me "no way is it the head gaskets on that engine" but hindsight is a wonderful thing and perhaps I should have listened! Unfortunately the same people were not offering any alternatives.

Both heads and block were cleaned and checked with a level, so not warped.

Anyway... Engine is back together and £1000 ish later it is doing the same thing

I am now of a mind to simply drive it to the nearest breakers yard and give them the keys. Before I do I am hoping that someone here can suggest something I may have missed.

This car has been the biggest lemon I've bought and I've owned close to 50 cars, but I'd still like to save it if it makes any kind of economic sense to do so. It's a fundamentally solid car with only 70,000 miles and I quite like it.

New engine is a possible I guess, but may just be another can of worms.

 

[roastbeef]

Have you checked basics
Thermostat not seized shut
Water circulating ie hot heaters not blocked rad
water pump still pumping not broken sheared
Don't know if that engine has cylinder liners but they can corrode?

 

[moonloops]

Sounds like a crack between cylinder(with or without liners) and the water jacket?

 

[pompeypetey]

Have you checked basics
Thermostat not seized shut
Water circulating ie hot heaters not blocked rad
water pump still pumping not broken sheared
Don't know if that engine has cylinder liners but they can corrode?

Thanks for the reply.

• Thermostat was changed around 6 months ago but I do have a spare which I'll try.
• Heaters are blowing hot. The water pump looks original although it has only a tiny bit of play and is quiet. Was planning to replace it anyway.
• The cylinders aren't lined (if you mean sleeved?), alusil coating I believe - stand to be corrected though. The inside of the engine was in remarkably good condition really. Almost no wear on the cams etc.

 

[bolide]

What results do you get from a compression test & leakdown test? Did you have the heads crack tested?

Nick Froome

 

[wu56Shoozz]

Weren't Alusil bores the ones that went porous like the Bimmers 740's etc?? Did you get the heads skimmed before replacing them?

 

[BULLITTBOSS]

Egr cooler???

 

[pompeypetey]

Not had a leakdown test done, will be doing so this evening hopefully! I don't believe my car has an EGR cooler, certainly don't remember removing or refitting it anyway

 

[MancMike]

If it's driveable, drive it to WBAC and sell it to them.

 

[pompeypetey]

If it's driveable, drive it to WBAC and sell it to them.

Hmm they think it's worth £1.2K. No doubt they would reduce that once I turn up though.

 

[brucemillar]

As has been said: Please be sure to re-check all of the basics. My 3.5 Pajero suffered a host of "overheating" issues after having both head gaskets replaced and the heads refurbished.

The single biggest and most concerning issue being the engine boiling up at idle or in traffic or a steep hill. This was finally (having pulled most of the cooling system apart) found to be a failing radiator cap seal. This was allowing the system to blow past the seal at low temp and was not noticeable to the eye. It was also a brand new cap, that I had fitted when I had the radiator re-cored. The seal inside the rad neck was the culprit with a microscopic imperfection that was enough to allow pressurised coolant to blow past. This was finally found when, by chance I spotted a tiny amount of (like one drip) of coolant around the rad neck. As I looked at the drip it evaporated in front of my eyes with the heat from the rad. Cost to fix £9.99

Three months on and not single boil up or loss of coolant. This from a position where every journey would see her boil up, making her unusable and about to be scrapped.

Whist looking for the cause I also found a strip of old head gasket wound inside the heater matrix inlet pipe. That was a small strip but enough to restrict coolant flow through the system.

 

[E55BOF]

The leakdown test will tell you if it's a crack somewhere. Let us know what was the result.

 

[grober]

Bearing in mind the " timescale to failure" most likely explanation is that the head/s did require skimming and subsequent failure of the new head gasket/s is down to that. If as I suspect the M113 has an open deck block that's perhaps more important than on some setups.

 

[pompeypetey]

Thank you for all the replies.

Leak down test seems sensible and a new rad cap should be arriving today. If it turns out it was that all along then at least I learnt how to replace the head gaskets, and I'll also keep a stock of caps in the boot...

I also think that having the heads and block skimmed might have been a wise idea regardless of the level suggesting it was fine, but I was trying to keep costs to a minimum. I was also under the impression that these engines should not be skimmed due to some type of special factory coating on the surface. Too much googling perhaps.

I've flushed the cooling system out very thoroughly so I'm fairly confident there is no blockage, but it's always a possibility so I'll pull the hoses off again and double check.

It is worth noting that the engine does not over heat. It gets up to temperature quickly and stays there even under load, or at idle. The only real issue is coolant being chucked out of the expansion tank under load after foaming for a while, and at idle it is pushed down in the tank which triggers the low coolant light.

I'll update later with the results of the leak down test.

 

[bolide]

Bearing in mind the " timescale to failure" most likely explanation is that the head/s did require skimming and subsequent failure of the new head gasket/s is down to that. If as I suspect the M113 has an open deck block that's perhaps more important than on some setups.

Ah - so the photo shows what an open deck block is? Exhaust gas in the coolant is pretty much a given if the block or either head is warped!

Nick Froome

 

[MancMike]

Coolant should be under pressure and so shouldn't boil as the boiling point raises due to pressure.

If you've a leak, even if no fluid is getting out, if pressure can escape, the coolant can "boil", giving off vapour which is lost.

Are you sure the system is gas tight? If you loosen the coolant cap when fully up to temperature, it should hiss and steam your fingertips off.

 

[grober]

Here's a picture of the related M112 V6 engine block. Normally these alloy cylinder head/alloy block engines do better than the old alloy head / cast iron block engines for CHG longevity "from factory" but I suspect once they warp/corrode may be more difficult to get those mating surfaces flat again.

Here is a picture of an early M119 closed deck block for comparison- later ones were open block evidently??

 

[gazz]

Does this car have an LPG system fitted by any chance?

 

[pompeypetey]

I've replaced a few host clamps now and touch wood I think it's behaving itself a little better. I'm still not sure about the expansion tank cap though, which is due today. It does not appear to be losing any coolant and the car does not have an LPG system fitted.

If problems persist I'll get the leak down test done.

Does anyone know what this vacuum hose is for? I can't remember for the life of me if it plugged into anything and I can't see anything obvious, although it was originally connected to a J shaped vacuum hose but I've replaced the lot with cotton braided.

 

[brucemillar]

I do not know about your vac hose - sorry.

A pressure test on your coolant system is cheap and effective, more so than looking for evidence of leaks, to start with. Leaks like this usually only happen when the system is pressurised so any leak is likely to be vaporised coolant and may not be visible to the eye. The other method is to get a luminous/type dye in the coolant then look for evidence of it having sprayed onto the engine or undertray etc. Some Antifreeze does have this in it. Check that it is the correct coolant for your engine. The wrong stuff can cause leaks!!