VZ with LPG - overheating problem cured

[TwoUpTourer]

For the record I'm putting up this thread in case it helps someone doing a search for this problem.

VZ Commodore with factory LPG.

Six weeks ago my VZ Commodore suddenly overheated, dumping coolant out onto the road. Topped it up, made it home before it did it again.
Did another top up, this time bleeding air out of the top of the radiator via the screw at the top right (from drivers perspective), ensuring it was all full. Ran it again, and lots of the coolant ended up in the overflow tank. Siphoned it out, put it back in the filler cap, bled the radiator, and after the next short drive it was all back in the overflow tank.

Mechanic I knew said I had a small head gasket leak and combustion gases under load were being forced into the coolant, displacing the coolant into the overflow tank, and suggested doing first a carbon-monoxide test of the overflow tank to see if that what was happening. Negative result.

Another mechanic said he was replacing head gaskets on VZs at the rate of 2/month that caused this overheating. This is really bad. And expensive. Wanted to do a leak down test to determine which cylinder was leaking combustion gas. Also time consuming = $$$.

Went to a third guy, a radiator specialist, who said honestly he didn't know. But he did know someone with a $20k testing machine who could definitely test for carbon monoxide gas in the coolant.

At this point I was pretty dejected, as the car is in great condition, but the engine is cactus. Lots of opinions on this forum, gaskets, thermostats, not bled properly etc, but none ultimately close to the actual cause.

So I went to the fourth mechanic, who didn't even get up from under the vehicle he was working on and immediately said to me that it was my LPG converter. What the hell??? Said it was a known problem, that after 100,000km, the seals are prone to let LPG into the coolant. Said to turn off the LPG at the tank, not just the switch in the car, so that it forces the car to run out of gas, and run it on petrol for a while to see if the problem disappears.

BINGO! Instant cure!
Rang the Adelaide distributor(MegaGas) for the factory installed gas system to get a seal kit, and he said 'sure, a well known problem!". Bugger me dead. Six weeks of grief, and all it took was asking the right guys. Kit was $87.

Found a local LPG installer who changed it over in 90 minutes for $100 labour.

Turns out the installation notes say that at various intervals the 6 screws holding the lid on the LPG converter need to be nipped up, because there are 2 large rubber sheets sandwiched between top and bottom of the converter, and over time the rubber softens a little, leaving slack in the screws, and allowing LPG to leak through to the coolant. Just great.

Whilst this little pearl of wisdom is in the installation notes, it is NOT mentioned in the LPG service manual, so therefore your local mechanic doesn't know that the screws require tightening. In my case, the LPG mechanic who installed my new seals said that my screws were barely more than finger tight, so LPG leaked through into the coolant, and LPG expands 270 times its volume into gas, causing large amounts of coolant to be forced out into the overflow tank, and ultimately onto the road. I have the old seals, and coolant has crystalised onto the surface at one point where there shouldn't be any.

So $187 later, what was going to be an expensive disaster is cured. If I had followed some of the advice I was given, I would have split open a perfectly good engine, spent a lot of time and money fixing something that wasn't related to the problem, and a week later be back exactly where I started, LPG leaking through the converter into the coolant.

I had a gut feeling that why would an otherwise good motor at less than 140,000km suddenly develop a weak head gasket, so the lesson was to ask, ask, ask until someone had advice that made sense. As soon as mechanic 4 said it, I just knew he would be right as it fitted all the symptoms. And it was so simple to test.
MegaGas in Adeliade said any car with LPG that has an overheating problem, should turn off the gas at the tank first and test if the problem disappears. Good and cheap advice.

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SEARCH TERMS: COMMODORE, VZ, OVERHEATING, COOLANT, OVERFLOW TANK, CONVERTER

 

[routier1642]

Good to know!

 

[Electro]

Wish I'd read this three months ago! Put new head gaskets on, surfaced the heads bla bla, still foaming and bubbling. Got a new motor - put that in, same problem. Every piece of advice from web sites and several mechanics was that I had a head/gasket/block problem - should have done a carbon monoxide test on the bubbles in retrospect. Thanks heaps for taking the trouble to post. I'm doing the test tomorrow over an extended trip but a short drive last night showed no foaming in the coolant. Fingers crossed!

 

[corhijasna]

yes very well written and thanks for the advice,i am sure it will eventually be used by someone out there,definitely in my memory bank lol

 

[Shorty33]

thanks for that narrative.

I'd suggest an additional search-tag: "one more reason to avoid LPG"

 

[Zeussy]

thanks for that narrative.

I'd suggest an additional search-tag: "one more reason to avoid LPG"

Yes, because nipping up half a dozen screws isn't worth the money saved on petrol...

 

[profat]

Very well written ,and as is often the case unless you work on a particular make of car or specialize in fuel systems, or transmissions you cant know everything .....cars are an expensive toy to both purchase and own......this is one for my memory banks even after 35 years im still learning ....thank you

 

[TwoUpTourer]

Wish I'd read this three months ago! Put new head gaskets on, surfaced the heads bla bla, still foaming and bubbling. Got a new motor - put that in, same problem. Every piece of advice from web sites and several mechanics was that I had a head/gasket/block problem - should have done a carbon monoxide test on the bubbles in retrospect. Thanks heaps for taking the trouble to post. I'm doing the test tomorrow over an extended trip but a short drive last night showed no foaming in the coolant. Fingers crossed!

So how did it go?
I really feel for you, as I was soooo close to going down the same path as you have, spending a fortune and a lot of time, so effing fruitlessly. I made a point of returning to each of the mechanics I consulted to let them know what it was, as some day it will appear on their doorstep.

The carbon monoxide test is of course useful when you are scrabbling around for a cause, but in this circumstance, it would have been negative, just as it was for me, because there wasn't any carbon monoxide. It was LPG. The real question would have been what is the next step to take with a negative test, because that would prove it is not a head/block problem. This is such an out of left field problem that all the usual indicators fail you, and it is only the experience of the gas guys that will help.

I should add that a month onward, the coolant is completely back to normal. Because the first mechanic was grabbing at straws, we put some powdery gunk in the coolant in case it might fix it, and it is still there, so this friday I have to do a complete system flush to get it all out before refilling from scratch. Better than changing motors though...

 

[Electro]

Yep - it was a leaking converter.

Car has been fine on petrol ever since. I've just got a new LPG converter and some LPG thread sealant and will put it in over the weekend. Funny thing was, I thought of the possibility of LPG getting into the coolant some time back and had a good sniff of the gas that was present when the coolant cap was unscrewed, but it had no LPG smell at all so thought it was must have been Carbon Monoxide from a leaking head gasket. So, another lesson I learned - the smelly tel-tail put in LPG gets totally dissolved out of the LPG when the LPG hits hot coolant. Without that tiny amount of tel-tail chemical, the LPG is odorless. A CO test would have confirmed that there was no combustion gas in the coolant, but I didn't do that...:-(.

And - I also put a sealant into the coolant like your mechanic has. It was a silica based compound supposedly for "permanent" repair of head gaskets and cracked blocks - yes, and I believe in father Christmas too. First time around, it worked, sort of confirming that it was a head gasket or crack, but within 5000 km, I cut the water pump out. I replaced the pump and 5000 km later, the next pump was leaking too. Bearings still good, but fluid seal was worn out. Seems those silica based sealants can abrade the water pump seal away ... found other folks saying the same thing on some forums in the US, especially if you use the heavy duty concentrate in the "head gasket fix" bottles. So, my second lesson was...don't use that stuff if you can help it.

So, I drained the coolant which still had the "head and crack sealer" crud in it, after all, it was a permanent fix right? Within a day, bubbling and overheating was back. Seems, I'd temporarily sealed the LPG to coolant leak in the LPG converter in hindsight. I put sealant back into the coolant, but it now refused to seal up.

After talking to a couple of local LPG workshops, none of them had heard of the VZ and VE commodore converters going leaky. Didn't fill me with confidence. Spoke to a guy in Adelaide and he said - oh it's well known. I do heaps of them.

Next question - put a new seal kit in the old converter or buy a new converter. His advice was that a new seal kit was a temporary solution, and the repaired converters seldom lasted very long. Well, having finally found someone who at least knew about this problem, I decided to take his advice and just buy a new unit and be done with it.

Hope this helps.

 

[TwoUpTourer]

Yep - it was a leaking converter.

- A CO test would have confirmed that there was no combustion gas in the coolant, but I didn't do that...:-(.

- After talking to a couple of local LPG workshops, none of them had heard of the VZ and VE commodore converters going leaky.

- Next question - put a new seal kit in the old converter or buy a new converter. His advice was that a new seal kit was a temporary solution, and the repaired converters seldom lasted very long.

Thanks for responding. This is such a difficult and mostly mis-diagnosed problem that any and all comment here will be useful to someone.

Regarding the CO testing, there are three ways I know of.
(1) The most common is what most mechanics have, being the small hand held sniffer with the rubber bulb on one end like a turkey baster. For a slow leaking head gasket there may not be enough carbon monoxide present when just puffed above the open coolant filler opening.
(2) A much better one is a type that screws on to where the coolant filler cap is, so there is no chance of the CO getting away, and it rises up through a reservoir that has some kind of oil in it into a chamber so that there is an opportunity for the CO to accumulate over a period of time without being dispersed. It like the hand held has a special fluid in it that changes colour in the presence of CO.
(3) Some fancy electronic gizmo that I didn't actually see, but is apparently very sensitive so may have been good enough for this task.

In any case, as we know, it was going to prove negative anyway for this situation. In the absence of getting the right advice we eventually got, a negative result would really have been a conundrum, because what the hell else could it be?

Regarding the choice of repair/replace, my gas guy said that some converters get a lot of corrosion, and he warned there was a chance that the allen screws may snap off and if so I would be up for a new converter. As it turned out, he said mine was perfect inside, and there was no reason at all to replace.

What do you reckon it cost you to firstly strip down the motor, shave heads, new gaskets etc, followed by an engine replacement? My guess is that even if you did the work yourself you would get no change out of $5,000.