So my old bus has always started lumpy.

It'll fire up with some cylinders missing, which is especially noticeable if you try to rev it up immediately after starting. If you just leave it alone, chuck it in reverse and back out the driveway, by the time you select drive and pull away its usually got all 8 firing just fine. Alternatively if you bring the revs up to say 2000rpm and just hold it there, you can hear it sort of sort itself out and the cylinders come online.

So cue the other day, i go out and start it at lunch time, after it having sat for best part of two weeks. It started, but sounded REALLY unhappy, like half the cylinders were missing. I tried to rev it up a bit, and the throttle was unresponsive, RPM's were super low and oil pressure light was on. Mashed the throttle a bit more and eventually the revs picked up a wee bit and oil pressure warning eventually went out but it was stumbling and generally running like absolute crap. It was about this point i realised it was pouring white smoke out the exhaust like a steam train.
Wondered if it had done a head gasket or something, but i had kids to collect from nursery up the road, so decided to drive it and see what would happen. Revved it some more to try and "clear" it up, and managed to fill most of the driveway with smoke, but it picked up a few cylinders and was now actually responding to throttle, so i set off.
By the end of the street it was running more or less normally, exhaust still appeared steamey, but its cold and well, not entirely unexpected given conditions etc.

Drove to nursery fine (perhaps a mile max), went in and got kid, and came back out, checked the coolant level which was low but ok (it leaks so its often low). This time it fired up easily and drove off without a problem. Drove to the sports center with no issues. Parked for an hour and a bit while in the sports centre.

When i came out of the sports centre, turned the key and it started, and again, wouldnt respond to the throttle, and this time was belching black smoke out the back... However after 5 or 10 seconds it sorted itself out and i drove home. Coolant level was still the same when i got home, so no massive water consumption.

So at this point i'm thinking head gasket or slipped liner or something... And its fixed itself...

Driven it multiple times since then with no issues whatsoever...

Any ideas?

Burn it

i think oldshep56 has hit the nail on the head .... unless you want to spend some money ?white smoke is steam so its leaking water in their somewhere, so heads off also some plugs and leads maybe desirable . a compression test will confirm this.

I did the heads on one that poured steam afterwards, never did get to the bottom of it, the guy sold it,, if you have a hg gone, pull the plugs, one will be extremely clean compared to the others, start rh back, that’s the favourite for going

Will need to check the plugs and look for signs of water.

Wife took it into town and filled it with lpg the other day, and we've done 85 miles today with no recurrence of the weirdness.

Much strange!

Do you have a stainless exhaust system ? They seem to like the steam train effect in the cold weather, not sure if they retain some moisture ?

If its on LPG you get more steam anyway in the exhaust as there is more water vapour in there. Though it shouldn't be as bad as constant clouds of it all the same, neither would that explain the black smoke that was mentioned?

Both my LPG vehicles make steam like crazy on a cold morning, especially a damp one. It's enough for me to wonder about head gaskets but one of them has had two in my ownership and it was always like that whether it needed a new HG or not. If you're not using amounts of coolant I don't think it's that.
Are you sure it's not oil burning? valve stem seals might be worth investigation.

Or the oil has been overfilled and it's blowing it out of the breather into the intake?

I'd be inclined to pull the spark plugs and see what state they were in at any rate, if you have the kit to do it doing a compression test at the same time might give you a bit more to go on.

I've had a piston get damaged enough on another vehicle to end up getting oil going back into the intake as it pressurised the sump too much as well as only really running on 3 cylinders properly (rings were chewed up as well as a hole through the actual piston itself) and that didn't get enough into the intake to notice any difference though it did coat the lower side of the air filter and box to the point where it started running down the front of the bumper. But its easy to have a look and see if oil is getting that far in the intake all the same.

LPG makes more steam than petrol, both are hydro-carbons of course but LPG has a higher ratio of hydrogen to carbon than petrol, so more H2O is produced in the burn, so more steam. But from what you've said it seems to me the amount of steam you're getting is excessive and coupled with the misfires on start-up this seems to point to there being a problem.

I agree with the potential issues others have already mentioned. An unlikely but possible other situation - If the LPG system's pressure reducer has a failed water circuit gasket there's potential for water from the cooling system to enter the LPG vapour lines and then to enter cylinders via LPG injectors... in effect you could have water injection via the LPG injectors giving misfires due to lack of fuel and overdose of water injection at startup until the water in the LPG lines is gone. Unlikely because usually with a failed reducer water jacket gasket you'd also have an LPG pressurised cooling system, so after a while of running on LPG have water blowing out of the cooling system and overheating issues etc. But I have known symptoms similar to yours, i.e. no over-pressured cooling system, overheating or great loss of water but water making it into LPG lines and misfires for a while after start-up.

Edit - other symptoms of cooling water making it's way into cylinders (by any means - HG problem or LPG reducer problem) also usually results in failed lambda sensors because antifreeze damages lambda's. A failed reducer water jacket gasket wouldn't usually cause misfires at startup because during warm-up the engine runs on petrol not LPG (with a sequential LPG system).

Mine made hell of a black smoke on startup when the failed fuel pressure regulator was dumping petrol into the plenum.

You mentioned it leaks - do you know where its actually leaking from? Or do you just see the level dropping and no sign of where its escaping to?

If its a reducer issue as Simon has described above, the simplest way to diagnose/fix it is to disconnect the water circuit of the reducer somehow and see if its stops the leaking. Either a pressure test on the cooling system, or run it on petrol and see if the leak stops like that (can't run it on gas without the water running through the reducer as it won't switch over anyway, and would freeze the reducer, which would probably cause it to fail anyway).

Also if you take the spark plugs out when its cold, are any of them shorted out by moisture? wouldn't need very much to cause them not to spark until enough petrol is thrown about when its running badly to get them working again.

It might have just been a combination of short journeys filling the exhaust with moisture, and yes, it is a stainless system after the cats.

But that doesnt explain the lack of willingness to rev or the black smoke.

It definitely burns oil at times, but that has a particular smell and thats not what i experienced here. The oil level is right on the minimum, because the sump leaks like a sieve if i fill it up to the max line :P This "smoke" was definitely water vapour/steam.

Interesting point from Simon on water in the LPG circuit, the LPG vaporiser certainly leaks coolant and its on my lsit of things that needs fixed. However on startup it was running on petrol and hadnt got warm enough to open the LPG valves, so i dont think its that in this case?

I made a video of a normal startup, unfortunately the audio quality isnt great and i'm not sure it really adds anything, as its not indicative of what it did last week, and its always done this on startup: https://www.youtube.com/watch?v=wSinJdHjfv0&feature=youtu.be

As for the water consumption, it definitely leaks, from multiple locations. Front timing case (usual spot at the top corner) and inlet manifold (big fitting that goes to the heater matrix) both seem to leak coolant from time to time, but it comes and goes. Similarly one of the T pieces on the LPG coolant leaks despite me replacing the Tee, the hose and all the clips...

I still need to pull the plugs, the weather has been awful so i've not managed it. I think i'll just buy it a new set while i'm there.

I've seen black smoke before with a failing MAF sensor, but that didnt clear, it just stayed and wouldnt go at all until i replaced the MAF.

I mean, the engine really needs to come out for some TLC, but i'm not rebuilding a rover V8 on my driveway in the middle of winter if i can avoid it :P

Usually once there's been a long term problem of coolant in LPG injectors / vapour pipes the LPG system won't work properly even after draining, coolant can damage injectors. It especially won't work properly while there's still coolant in them. If a reducer water gasket is blown water could still find it's way into the injectors/vapour pipes even running on petrol because the seal between water and gas is blown so even with no gas entering from the tank water can find it's way to the reducer gas outlet... But wouldn't usually find it's way into cylinders because injectors still provide a seal when closed... unless coolant has damaged injector plunger seals or coolant pressure rises very high. Blown reducer gaskets can also cause coolant pressure to rise high (potentially to LPG tank pressure if the headgasket etc could stand that much pressure which it can't!) but only when the gas valves have recently been open.

Not saying any of this is the problem, just giving more details about effects/implications of a reducer gasket problem.

Any smoke during the video startup? I didn't pick up on anything much in the video, few clangy noises which could be just exhaust noise / cam / lots of things. Was it running on all 8? Would it rev higher if you tried?

If its leaking coolant from the vapouriser, theres every chance its also leaking coolant directly into the intake manifold via the vacuum connection. IT would still be able to do so whilst running on petrol as that side of the system is not shut off when its on petrol (as if its working properly all it should be doing is pulling on the diapgraghm so no problem there).

All the other leaks to me suggest you have too much pressure in the cooling system for some reason - this can be down to gas leaking from the vapouriser into the coolant.

If you want to test that further, bypass the vapouriser on the water circuit (connect the two coolant hoses running together to each other) and run it on petrol.

it runs sweet on LPG tbh... so while the things leaking externally, i guess its probably fine inside. Still needs replaced though!

BrianH wrote:

If its leaking coolant from the vapouriser, theres every chance its also leaking coolant directly into the intake manifold via the vacuum connection. IT would still be able to do so whilst running on petrol as that side of the system is not shut off when its on petrol (as if its working properly all it should be doing is pulling on the diapgraghm so no problem there).

All the other leaks to me suggest you have too much pressure in the cooling system for some reason - this can be down to gas leaking from the vapouriser into the coolant.

If you want to test that further, bypass the vapouriser on the water circuit (connect the two coolant hoses running together to each other) and run it on petrol.

Good point on the vac line didnt think of that. Like i say, once its run for a minute or so, it drives fine, LPG works as it should etc. Did 150 miles in it at the weekend with no probs at all.
It just seems to leak from everywhere. So perhaps there is some pressure getting into the coolant system from somewhere?

The black smoke and lack of willingness to rev sound like fuel control issues, certainly no indication of a need for engine overhaul.

Once it's up to temperature, how hard is the top hose? It should be firm but not rock hard.