Spark plugs

[stewartw]

I have an 07 Merc A150 on gas, its due a service soon, I've been reading about how spark plugs can effect the running.

Are standard plugs ok, or do I need specific ones like platinum?

Thanks

[Gilbertd]

Most people recommend you DON'T use platinum plugs in LPG vehicles. If the standard plugs are normal single electrode ones, use those and close the gaps up to 0.8-0.9mm. If the standard plugs are the twin or quad electrode type where you can't close the gap, then you are better off going for Iridium. They may be more expensive but will last a lot longer. The same set have been in my Saab since I got it and it's done 33,000 miles since I've owned it (and they didn't look new when I got it). Some people have got over 50,000 miles out of a set.

[stewartw]

How do you close the gap?

[Gilbertd]

You could use a small hammer although I tend to whack them with a screwdriver handle. Although I have been known to bash them against the garage wall.....

[Clifford Pope]

Don't ever hit a plug, or drop it. They are fragile and can get an internal crack not visible externally.

There is/was a special tool for bending the side electrode, but what I do is very gently nip the plug end-on in a vice. That way you can close it up a fraction in a controlled way without risk of overdoing it and having to bend the electrode back again.

[SimonHobson]

The same set have been in my Saab since I got it and it's done 33,000 miles since I've owned it (and they didn't look new when I got it). Some people have got over 50,000 miles out of a set.

I take it you remove them periodically to check them ? I've had problems in the past with corrosion* forming on the bit of thread that's protruding into the cylinder - and then when you come to remove them, you're wondering how much of your soft aluminium head is going to come with it

* Yes rust - Rover V8, end cylinders, need i say more

[Gilbertd]

On the Saab they are nicely protected by 'bungs' incorporated in the plug leads and a cover over the top of everything as the plugs are central in the combustion chamber. With 4 valves per cylinder and a pair of overhead cams, the plugs lurk down the bottom of a very deep hole. No way any water is going to get to those and I copperslipped the threads when I took them out to see what state they were in when I first got the car.

The Ran Over was treated to a new set of plugs just before I got it (along with HT leads, dizzy cap, rotor arm and coil), in an effort to cure the intermittent starting problem. They are Bosch ones but I suppose it's better than nothing (or Champions even) although I'd have preferred to have found a set of NGKs in it.

I've also found the reason for the non-starting and occassional cutting out once running. The (@!##) Lovato gas controller had lost it's settings so unless you manually switched it to petrol it was trying to start on gas but it couldn't because the ignition switched feed had been taken from the auxilliary supply which turns off while cranking. No ignition switched supply means no solenoids opening so no gas! The occassional cutting out was due to the vaporiser being the highest point of the entire cooling system (with the hoses running over the top of the plenum chamber) so guess where any air ended up! The thick layer of ice on the entire outside of the vaporiser and the strong smell of propane was a bit of a giveaway.

[SimonHobson]

On the Saab they are nicely protected by 'bungs' incorporated in the plug leads ...

I was referring to inside the engine. On the V8, the plugs protrude a couple of threads into the combustion chamber - and I;d had one where the end threads had gone rusty.

I've also found the reason for the non-starting and occassional cutting out once running. The (@!##) Lovato gas controller had lost it's settings so unless you manually switched it to petrol it was trying to start on gas but it couldn't because the ignition switched feed had been taken from the auxilliary supply which turns off while cranking. No ignition switched supply means no solenoids opening so no gas!

A right numpty fitted that then

The occassional cutting out was due to the vaporiser being the highest point of the entire cooling system (with the hoses running over the top of the plenum chamber) so guess where any air ended up! The thick layer of ice on the entire outside of the vaporiser and the strong smell of propane was a bit of a giveaway.

Been there, done that, got the tee shirt.
Interestingly, I can tell you that an OMVL will be playing up in a few yards without any water flowing, while the Romano in the 110 will (just) manage 5 miles with no water. I think you can imagine what the Romano looked like after that

I know this is where Rossko and I disagree, but I put the reducer in series with the heater on Ran Over, Disco or 90/110. Either join back together, or replace one of the heater hoses down the back of the engine, run another hose from the heater to the reducer, and then from the reducer back to the connection on the metal pipes down the right of the plenum cover. You're pretty well guaranteed a positive flow then (unless there's enough air to airlock the pump), AND you can tell there's flow from the heater - if it suddenly goes cold you know the reducer has just frozen due to low coolant (V8 head gaskets strike again).

[Gilbertd]

Interestingly, I can tell you that an OMVL will be playing up in a few yards without any water flowing, while the Romano in the 110 will (just) manage 5 miles with no water. I think you can imagine what the Romano looked like after that

A Lovato will manage about 500 yards......

I know this is where Rossko and I disagree, but I put the reducer in series with the heater on Ran Over, Disco or 90/110. Either join back together, or replace one of the heater hoses down the back of the engine, run another hose from the heater to the reducer, and then from the reducer back to the connection on the metal pipes down the right of the plenum cover. You're pretty well guaranteed a positive flow then (unless there's enough air to airlock the pump), AND you can tell there's flow from the heater - if it suddenly goes cold you know the reducer has just frozen due to low coolant (V8 head gaskets strike again).

I intend doing just that, if nothing else but to tidy things up a bit. I intend putting the vap in the flow rather than the return which appears to be the outer one of the two (with the fill tower). There's no sign of any head gasket problems but it does use a bit of water although I suspect through poor joints (a few drops of water on the floor when I pull away after it's been stood for a few minutes would seem to confirm that). As it originally had air suspension and now has coil springs, there's a big vacant space where the top of the air suspension unit used to live so the vaporiser is going down there. Just need to get some assorted hose for the coolant and gas pipes.