Lifter noise? under load

[Happy]

My 3.8 VT gets a noise like a clicking lifter when I'm half way up a very long hill but only when towing my caravan (ie under load) & it disappears as soon as I ease off.
I'm on dual fuel but run on LPG.
When this happens the engine smells subtly different. Once 2 years ago when this happened the hot sign came on.
Despite devoted tuneups & tests it still happens.
Does anyone have an insight as to what it may be?
Any thoughts would be appreciated.

[chargedvx6]

Do you have a beefy trans cooler on the car? The noise may be trans related. Maybe try running the trans fluid level at about 1cm over the hot/full mark. You may be running a tad low when it's going up hill under load

[Happy]

Standard trans cooler only. Higher oil level is worth a try although the soft clicking seems to be at lifter frequency.
Can detonation occur on one cylinder without the knock sensor correcting it?
If borderline lifter has anybody had success with an oil additive to clean the lifters?

[graham7773]

Lifter free, Nulon I think. Will work if it is just dirty lifters. Are you running synthetic oil? and regular oil changes? That helps as well. As for a single cylinder pinging, yes, esp if there is a little bit of carbon/coke sticking up in the combustion chamber acting like a glow plug. knock sensor will try to correct but it is not a timing issue.

[Happy]

It is regularly pampered with Helix 15w 50 synthetic because of the LPG. I will get some Lifter Free tomorrow and cross my fingers.
Dont like the idea of taking the heads off for a decoke.
Cheers

[graham7773]

A bit more about coke. If you can find some Redex upper cylinder lubricant, take your plugs out and put about 20 ml in each cylinder. put the plugs back in and disable your ignition circuit. spin the motor over for a few seconds and let the car sit over night. in the morning, turn the motor over again. remove the plugs and put some rag over the plug holes then turn the motor over again for a for about 10 seconds. Gets rid of the bulk of the Redex. clean your plugs (or change them if they are due) then start the motor. Don't be concerned about your street disappearing in a cloud of smoke. This won't last very long. this job will usually remove loose coke. next option is heads off. Hope not for your sake.

[Happy]

That sounds like a brilliantly simple approach to decoking. I haven't heard of Redex since Jack Davey went on the Redex Trial in the 50s and Gelignite Jack Murray blew up the outhouse.
I'll find some and follow your steps.
Has to be better than dribbleing rice into a revving engine years ago. The side draught carbs blocked up, the engine stalled and everything had to be dismantled.