My heater is going cold at idle, though my LPG vapouriser is staying hot - you can feel the difference in the pipes. It is currently plumbed in parallel, so presumably the flow is going mostly through the vapouriser at idle. My heater core is leaking at the o-rings and needs replacing one way or another (Audi route), but I'm trying to decide whether to keep the parallel setup or put the LPG in series like I did on my old car. I wonder if the o-ring leak is causing a bit of an air lock at the top of the 'kinks' in the heater hoses on the engine side.

Strangely, the return from the vapouriser has been plumbed into the hose going to the header tank, probably because it made things a bit neater.

Looking at this diagram, if I were to go series, I'd much rather use the return line from the heater core (22) as the feed/return to/from the vapouriser. It would make fitting much neater and avoid any high points in the pipework. But... obviously some heat would be lost through use of the heater. I know that in winter, this will mean it will take longer to switch over to LPG, but once warmed up, does anyone think this would be a problem?

I can't see it being a problem, I doubt if you'd even notice a difference in switch over time either, these things get warm so quickly.. I'm looking at doing the same with mine, it's bloody ridiculous that they plum the vaporiser in the way they do, my hoses are higher than the expansion tank,, I have lots of fun bleeding it, lol, have to lift expansion up as far as I can,,

FWIW. mine is plumbed in parallel with the Heater core - tee'd into pipes 21 and 22*. It changes over to LPG very quickly. In fact I'd ideally like it to wait a bit longer as it switches over before the ECU has switched out of cold idle and it goes a bit rough at idle until the temp comes up a bit more but that's just a software tweak. When the coolant is up to temp the heater is nice and warm. It does take a little while to produce heat but I've no reference with an unconverted P38 and with working heated seats (thanks again, Marty) and the electric screen - who cares?

*from memory, I'm 90% sure. Can check if you like

In Ferryman's thread I recommended plumbing it in series and fitting it in the flow hose (number 21 on the diagram) which is how I've got both of mine and the Classic I had before. But, if your reducer is installed where putting it in the return will make it neater, then I can't see a problem. In fact, on the multipoint system on the SE, putting it in the return would have been a bit neater. The return may be a couple of degrees cooler than the flow but it's doubtful it will make a lot of difference.

They do heat up quickly. This morning though I felt none of it while waiting for the windscreen to clear. My heated screen doesn't work at all either :( I'm not really bothered by that though, because of how quickly the engine warms up, I just need to be able to get it into the car.

My seats do now work though! But a hot arse is no good if you can't see where you're going, and I can't sit there keeping the revs up at 6am either - no centre silencer.

My LPG does switch over quickly as it is - sometimes questionably quickly, might have a dodgy sensor there too, but I haven't checked nor has it caused a problem yet. I'd somewhat prefer it take a while longer to give the petrol injectors a bit of an excercise. I don't want them gumming up through lack of use.

I think I'll go the return route then.

On the GEMS its easy to go from the supply to the heater and that's what I did on my old P38. On the Thor though with the vapouriser on the same side, its a bit of a mess. I want to be able to retain the ability to sort of remove the rocker cover (at least enough to change gaskets, which I currently can), avoid high points, and get to other bits and pieces in the vicinity without removing coolant pipes. If I go from pipe 21/the heater supply, by the time I've got pipe reducers and angles in, its not going to be pretty getting over or under the return line. Going from 22/the return though should actually be pretty neat and serviceable.

I changed my P38 and the Classic as both were suffering problems with parallel plumbing. The P38 heater would drop to vaguely lukewarm when idling in traffic in the winter and the Classic would ice up the vaporiser within 3-400 yards on a cold morning (see below). Changing to series plumbing cured both problems. With the coolant having a choice of routes to take, it'll take the easiest one so whichever is less easy will suffer. The reason a lot are plumbed in parallel is because on a car where the heater temperature is controlled by a valve in the coolant flow, with it in series and the heater turned off, there's no flow through the vaporiser/reducer. Installers will plumb in parallel as that will work no matter if the heater is full flow (as ours are) or variable.

This is what a vaporiser looks like with insufficient coolant flow......

This is something i need to investigate for mine.

Anyone fancy posting some pics of "tidy" installs?

Mine is plumbed in series, with the heater pipe split at "21" in the diagram there (the diagram looks like it's for a Thor but the heater bits make no real difference). It was okay in cold weather before I changed it - it was parallel when I got it - but could get a bit arsey on very cold damp mornings.

Being singlepoint mine doesn't have temperature switchover and it's programmed to just start on gas. By the time I've driven to the end of the farm track on all but the coldest mornings it's taken the chill off and I just drive gently for the first half a mile or so.

On a Thor, the return (22) is basically in the way of the feed (21). Whereas on a GEMS, it comes out of the bulkhead and then points straight down to the split to the header tank and metal pipework down there. If I remember rightly anyway.

Ordered a meter of 16mm silicone 1 ply hose like Richard suggested for the throttle body hose. That 8mm stuff was good, so hopefully the 16mm is too. Should make it a bit easier to fit in.

heated screen doesn't work at all either :(

Whenever I've had screens not working, always found it's the earth tags have come unsoldered, if, when you change the foam under the panel with wipers, your come across them, centre of screen,just plonk the soldering iron on them and they normally reattach. I love my heated screen 😁

When I first got it, the passenger side did work mostly, but the drivers side not at all. So hoping it was the earth tags or a faulty relay I investigated, but when I got around to it, by that time the passenger side had failed too, and it turned out to be the positive tags both end :( Not sure if you can get to those, I didn't try taking any exterior pillar trim off - assumed that was that and left it.

**no10chris

Whenever I've had screens not working, always found it's the earth tags have come unsoldered, if, when you change the foam under the panel with wipers, your come across them, centre of screen,just plonk the soldering iron on them and they normally reattach. I love my heated screen 😁

Hmm, another excuse to fit the foam I bought months ago but never got around to doing. This was mine a couple of winters ago but by last winter I was down to only a couple of strips on the passenger side and one thin 1" wide clear strip on the drivers.

If you have odd strips working, it won't be the tags sadly :( The bond wires in the screen itself will have failed.

Going to park up my P38 until I can sort this all now. The dripping from the heater is worsening, can't put it off any longer.

Gilbertd wrote:

**no10chris

Whenever I've had screens not working, always found it's the earth tags have come unsoldered, if, when you change the foam under the panel with wipers, your come across them, centre of screen,just plonk the soldering iron on them and they normally reattach. I love my heated screen 😁

Hmm, another excuse to fit the foam I bought months ago but never got around to doing. This was mine a couple of winters ago but by last winter I was down to only a couple of strips on the passenger side and one thin 1" wide clear strip on the drivers.

Time for a stone to mysteriously hit the windscreen, lol

Well this plan might be falling apart already. Now have two broken cars. Rear ball joints on the passenger side of my BMW seemed to suddenly start making an embarrassingly loud creaking noise this morning. But hey, with a working diesel heater, it was warm!

This is how I plumbed things together, not the finest example of a neat install but it works. Indeed on advisory of Richard I plumbed it in series, I had to deal with some issues.

The vaporiser has the heaterhose in- and outlet opposite to the gasoutlet, this tube I wanted to keep as short as possible without too many bendings. This explains the waterhoses going back and forth a bit odd to the point where I adapted them (returnhose 22 in the drawing). This is a temporary setup, I'm playing with the idea to bend the steel part of pipe 22 some 90º towards the vaporiser to simplify the return from vaporiser. At first this hose kinked when hot and I used the bended part of an old gems tophose (bypasshose 14 in drawing) to overcome this, again it's temporary.

Another issue is that the vapouriser's in- and outlet are 14mm dia while the heatercore pipes are 21mm and 19mm. I worried about the flow when mounted in series. Richard told me that the internals of the heatercore are 15mm too so some restriction was there anyway. I installed the vapouriser just below the expansiontank's cap and there is no problem with airlocks. I tried the heating at max and the interior and vapouriser stay hot, well it hasn't been cold yet but I'm pretty confident.

Aha, so you've done exactly what I want to do. My inlet/outlet on my OMVL vapouriser are in different places, but I have some silicone 90 degree bends and adaptors, so it should all fit in fairly nicely.

That's the biggest problem with trying to advise on the neatest way of running the plumbing, every make of vaporiser has the coolant pipes in a different place or orientation. So what will work fine on one will be a real 3 dimensional birds nest on another. Then of course there's the slight, but pretty significant, differences in coolant runs between Thor and GEMS. Just to make it even more confusing, the best place to fit the vaporiser on a single point is on the other side of the car so it keeps the gas hose run to the throttle body short (and there's a lot more space) but then the coolant hoses are on the opposite side.

And this is a LHD, so no steeringshaft in the way. But I like your comparision with the 3 dimensional birdsnest. I like birds (not frogs).