D2 4.0 LPG/Coolant problem

Apologies for the length of this one.
My engine developed a tapping noise month ago and after trawling here, I deduced it was worn hydraulic lifters having flushed the engine and used thicker diesel oil to no avail.

Into the fixers it went, heads off, new lifters, cam checked for wear, new timing chain, refitted a pair of spare heads which had been skimmed and pressure checked, new gaskets all round, back to me it came mended. It still ticked but I was told the new lifters needed a good run at a couple of 1000 rpm to bleed.

Last week noticed the water temperature was rising above normal and that the lpg guage was showing green lights and the bright orange light (Prins multi point system, it should be either/or). By the time I could pull over, the temp was in the red and the warning light was on, distance of half a mile tops.

Ignition off, bonnet up, smelt really hot with water vapour residue everywhere. While I waited for it to cool, I noticed the cowling over the viscous fan had not been fitted properly and there was a groove cut in it. Deduced it had dropped down, slowed the fan right down and caused the overheat. Cured that and everything was fine for a day.

On the way into work, the temp guage went sligtly above normal, but nowhere neqar the red, but that was it, lpg showed normal lights. Parked up and later noticed a pool of fluid under the car. Checked the coolant level, it was down, put in more coolant and tightened down the cap. Drove home, car overheated, gas guage went daft again, pulled over, no sign of the cowling fouling. Waited for it to cool down and recovered it to the garage.

The garage checked and found the thermostat was broke, changed it and everything is back to normal. The temp stays normal, the lpg changes over when it should. All is well.

However, I noticed today that the coolant level is down again and when I took the coolant cap off, there is distinct smell of gas.

When it overheated, have I melted something in the lpg system that is now pressuring the coolant level and dumping coolant. There is no oil in the water or vicky verky and all the spark plugs appear normal, so I don't think its head gasket or liner slippage, or, I bloody well hope not 120 miles since having the heads off and the big bill that entailed.

Anyone got any ideas. I've run it on petrol and the coolant level seems to stay the same, but on gas it drops. how does gas get into the coolant as I thought my 10 bolt heads didn't have cooling channels in them?

As ever, any advice is appreciated.

Well the only thing I can think of is the vaporiser, it warms the gas up using the coolant. whether there could be a leak in that letting gas into the coolant I don't know.

i would be inclinned to run on petrol ensure you have no more over heat episodes first this will prove it is the gas system causing the fault. or did the garage do their job properly and bleed the system.
as for the tappets load of cobblers if you have fitted non gen followers you will be back for more very soon. was it a standard or uprated cam was it ran in properly?

Thanks guy's. Sounds like another trip back to the menders to change the vapouriser then.
I believe the coolant system was bled correctly. It all now seems ok on the cooling front in both gas and petrol as I've driven around 50 miles since the thermostat change in what would be called, an enthusiastic manner, to see if I can get it to re-occur. It looks like the thermostat was intermittant and changing it cured the cooling issue. It's the re-occuring smell of lpg when the cap is removed and its been run on lpg that worries me.

The cam (standard) wasn't changed as it showed no signs of wear, only 2 lifters were dished and the lobes were checked, so the old cam was left in. That might have been a false economy.

The tapping has gone from constant to intermittant, and I only hear it because I know its there, it sounded like a toffee factory before. Maybe the oil pump is not putting out as much pressure as it should. Bring back proper guages instead of lights!

if the tapping is still there it could be down to a hair line crack in one of the hydraulic lifter bores, i have come across this only twice but if changing lifters has no affect then it could be the cause ? as for over heating, surely if the engine got hot before the vehicle went in to the garage the should of fitted a thermostat as a mater of course ? and the coweling well ???????

as for the lifters, if they are worn then the cam is too !!!