When I was researching before installing my LPG kit, I read that the ideal running temp. for the vap. is around 50degC, so I'm not sure if I've got a problem or not.

The car is a 1990 BMW 320i E30 touring running closed-loop (Leo) with a R90E vap. The vap. is mounted behind the n/s headlight and it's that close to the light unit that I had to discard the headlight cover because it wouldn't go in without butchering it.

When running, the vap. is around 50deg. However, as soon as the car stops moving (junctions, traffic lights, etc) the vap. temp. quickly rises and if the engine is left idling long enough it peaks at just over 70deg. As the temp rises, so does the engine's idle speed. I should, perhaps, point out that the engine temp on the guage is fairly stable - as in it doesn't rise anywhere near as fast as the vap. temp.

TBH, this vap. temp. issue has always bothered me slightly because of what I read in the past. However, recently it was pointed-out to me that the vap. temp. could be being held down when running by "wind-chill" due to the vap. being in a draught from the air coming in around the headlight.

So now I'm wondering.....
1) What really is the right running temp for the vap?
2) Should I shield the vap. from the air flow?
or
3) Do I need to find some way of keeping the temp. down at idle?
4) Could the 20deg variation cause any issues other than the rising idle speed (which TBH I've learned to live with)?

TIA
Stuart.

the vap temp is your coolant temperature, 70 degrees is fine, mine goes upto 80+

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Mondeo ST24, ESGI II

The temperature of gas (ie LPG vapour) going to the the engine will increase at idle.

As already pointed out vaporiser temperature is the temperature of the coolant leaving the vapouriser water jacket returning to the engine nd that normally is pretty constant in the range 80 to 95 just below the engine coolant temperature.

Idle speed should be controlled by the petrol ECU operating the idle speed control valve.
In normal petrol running during prolonged idling the temperature of petrol in the injection fuel rail increases this can cause petrol vapour locks, this effect will be magnified when running on LPG.

Many older petrol injections engines have a fuel (ie petrol injection rail ) temperature sensor. if the petrol ECU detects the fuel rail temperature rising it increases the idle speed by opening the idle speed control valve to increase petrol flow through the fuel rail so cooling the fuel and preventing petrol vapour locks.
Obviously when running on LPG this will have no effect on fuel rail temperature as the petrol in the fuel rail isn't going anywhere.

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"My friend: There's no safer investment than property in Pompeii."

I've never heard that one before. It is unacheivable in practice, without introducing some dinky thermostat or suchlike. Maybe its a misreading of "if it drops below 50C there is something wrong"

How are you checking temperature? Never seen an R90 with a sensor, though its not impossible to fit one.


If your engine temp gauge is at all vague it might be a clue ; modern engine thermostats seem to fail as often as old fashioned wax ones, but failsafe ... and secretively. You might have a goosed stat, and should at least check.

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www.blazegas.com

Thanks for the replies chaps.

There's a threaded blind hole in the top of the body of the R90. Optional sensor screws in and connects to the Leo and the read-out shows on the parameters page.

The car has had at least 3 new genuine BMW thermostats since I fitted the LPG. The latest one was less than 9 months ago when I rebuilt the engine. The guage doesn't appear to be at fault as at one point I had a different instrument cluster and the guages on both clusters show(ed), as near as makes no odds, the same.


So, does anyone have any idea what the "ideal" running temp. for the vap. is? I'm talking in terms of engine running quality and performance/efficiency here.

The ideal temperature is any temperature that the gas can vaporise properly at. The density of the gas will alter with temperature but the Leo should alter the stepper to keep the mixture, and hence the idle speed, stable. Unless the idle limits have been set too tight in the software and it is reaching the limits before it reaches the optimum at any particular temperature.

While there is the space for the temperature sensor on the R90, you must be the only person in the country to have one fitted! I've never seen one or felt the need to fit one.

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'96 Saab 900XS, now gone to a new home......
'93 Range Rover 4.2 LSE, Single point Lovato LovEco and R90E vaporiser (now).
'98 Ex-Police Range Rover 4.0, Single point AEB Leo and R90E vaporiser.

Is the sensor giving the temp of the gas or the temp of the coolant in the VAP?
If its the coolant temp, check the reading from cold and compare it to the temp reading from the standard engine coolant sensor.

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Mondeo Mk3 2.5 V6 Ghia X Estate with KME multipoint lpg system

As everyone keeps saying, there isn't an ideal temperature.

As the vap is plumbed into the heater water circuit (isn't it?) it should rapidly reach around 80C and stay that way. If it doesn't, there is a plumbing problem.
It really shouldn't drop that much when bowling around either, except under sustained heavy demand. Wind chill is likely to cause your sensor to read a bit lower, yes, but that doesn't reflect the internal temperature. Using that 50C as a guide to the minimum in-flight temp seems a good idea, if it goes lower it won't necessarily cause a running problem but it would be telling a tale that there is a plumbing or vap sizing issue.

If the gas system operation is very temperature sensitive, there is something wrong. Perhaps the gas mixer is fitted in the wrong place in respect of an idle air by-pass or suchlike.

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www.blazegas.com

How do people get their system to "autoswitch" then? When I first fitted my system, I had it set to switch on deceleration but could never remember to switch from petrol to gas first thing in the morning, once the engine temp. had gone up a bit. So I bought the sensor and let the system remember for me.
Mind, these days I have a garage and it usually starts on gas from cold unless it's had to stand outside all night in the depths of winter.

Thank you Rossko, that's the answer I was looking for.
I'll find something more important to worry about.

Just leave the switch in the gas position, start the engine, blip the throttle to above the changeover revs threshold and it changes over as the revs drop. I normally set the threshold to around 1,300 rpm.

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'96 Saab 900XS, now gone to a new home......
'93 Range Rover 4.2 LSE, Single point Lovato LovEco and R90E vaporiser (now).
'98 Ex-Police Range Rover 4.0, Single point AEB Leo and R90E vaporiser.

^^^ IIRC I tried that setting and I couldn't get it to switch-over without stalling. Probably something I did wrong when I installed the system.

Any rate, it's not a problem now.

Changeover delay. In the software you can set the delay so it turns the gas on before turning the petrol off. It gives the gas time to get there. The default is 0.5 second if I remember right and I had to change it to 1 second on my Range Rover to get a clean changeover.

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'96 Saab 900XS, now gone to a new home......
'93 Range Rover 4.2 LSE, Single point Lovato LovEco and R90E vaporiser (now).
'98 Ex-Police Range Rover 4.0, Single point AEB Leo and R90E vaporiser.

Mine won't switch over with a blip of the throttle unless the car is already warm and has been running on LPG previously, I imagine it's to do with the 2 feet of vapour hose I have to run?

Mine is set to switch over on deceleration, but needs a healthy 4-5secs on the overrun before switching over when cold, I do wonder if my stepper is on it's way out, is there a way to test them?