fox889 Posted April 21, 2012 Report Share Posted April 21, 2012 I've read loads of comments on the use of lead substitute & general fuel additives on here which has now got me scratching what little hair I have left. This is what I have: 1973 TR6 CR with 75k genuine miles on the clock, the last owner of 14 years used Castrol Valvemaster and/or Wynns Lead substitute. The engine is not pristine, the compressions are down a bit but she doesn't smoke, shake, rattle or roll. Oil pressure is 45/50psi hot @ 2000 rpm. In general she runs as good as she's going to under the circumstances. I've got one of K Raven-Smiths recon metering units to go on when my back straightens up........so my question is this: Do I use standard unleaded with one of the additives above Do I use super-douper unleaded with one of the additives above Do I use no additive at all with either standard or super-douper unleaded. Thanks in appreciation of your help Nick. Quote Link to post Share on other sites
Peter Cobbold Posted April 21, 2012 Report Share Posted April 21, 2012 Nick 75k is nothing for these engines - you've another 100K to go before the bores might get a bit tired. But I had a problem at that mileage - a long time ago - with a 1974 CR engine that cracked three standard pistons ( not burned, cracked across crown down to oil drain slot) So watch out for slight misfiring and hint of oil smoke and oiling a plug. New pistons solved the problem. I have yet to be convinced that road-driven 6 cylinder engines suffer from exhaust-valve set recession. They are slow revving in normal driving so may never get hot enough to start microwelding/recession. But if you do a lot of motorway driving at the speed limit without overdrive then the seats might be getting into erosion territory. I'd keep using one of the additives - just as insurance. Not a good idea to change from one to another as PO had done, unless they both use the same chemistry. Compression on standard engine will be 9.5:1 so 95RON probably not enough octane, you might hear pinking on acceleration. 97RON should work fine without octane boosters. You could try 95RON with the additive ( check it adds some octane ) and see how it goes. I am not convinced that the original MU needs changing. When lead was removed from petrol the octane was restored by adding toluene and other nasties that caused seal failures. But they have now been replaced with ethanol. So seal swelling may no longer be an issue. However the ethanol content might need a slightly higher fuel flow. If the PI is working fine I would leave well alone. Mine lasted 200K miles with no attention, and only needed fuel pump replacing becasue it started to leak into the wheel arch. Mind you it was daily driver, which probably helped with longevity. Peter. Quote Link to post Share on other sites
Denis Posted April 21, 2012 Report Share Posted April 21, 2012 I've never found Additives made any differance...so I just use Shell V Power, it runs fine! Quote Link to post Share on other sites
fox889 Posted April 21, 2012 Author Report Share Posted April 21, 2012 Thanks chaps for your thoughts, much appreciated! Nick. Quote Link to post Share on other sites
Grabea Posted April 25, 2012 Report Share Posted April 25, 2012 I've always used valvemaster plus, started using it in my XJS with 95 unleaded, anyone fancy a head job on a V12-thought not!, and am now using the same combination in my 6, more for insurance than anything and the octane boost is a useful bonus, also it's cheaper than super unleaded with standard valvemaster! Regards Graham Quote Link to post Share on other sites
RogerH Posted April 25, 2012 Report Share Posted April 25, 2012 (edited) Hi Nick, an old untouched engine will have plenty of lead stuck to the valve seats. With normal driving you should get another 30K miles out of it. It's only the exhaust valves that wear so occassionally keep an eye on the tappet gaps. When it all goes pear shaped get the head sorted - long term cost efective and no messing around at the pumps. Castrol Valvemaster does work wonders if your engine suddenly starts to do silly things. Last year in Scotland mine refused to go up hills. Don;t know why. I put some valvemaster in at the next fill and all was back to normal. Haven't a clue why. Roger Edited April 25, 2012 by RogerH Quote Link to post Share on other sites
Davidw Posted April 25, 2012 Report Share Posted April 25, 2012 FWIW, mine definitely runs better on 97 with Valvemaster Plus than on 95 with the same. Quote Link to post Share on other sites
Peter Cobbold Posted April 25, 2012 Report Share Posted April 25, 2012 Hi Nick, an old untouched engine will have plenty of lead stuck to the valve seats. With normal driving you should get another 30K miles out of it. It's only the exhaust valves that wear so occassionally keep an eye on the tappet gaps. When it all goes pear shaped get the head sorted - long term cost efective and no messing around at the pumps. Castrol Valvemaster does work wonders if your engine suddenly starts to do silly things. Last year in Scotland mine refused to go up hills. Don;t know why. I put some valvemaster in at the next fill and all was back to normal. Haven't a clue why. Roger You had a tank of stale petrol which was diluted at the next fill? Peter Quote Link to post Share on other sites
RogerH Posted April 25, 2012 Report Share Posted April 25, 2012 Hi Peter, if only. I was in the middle of a 2 week Scots tour. There may have been water in the tank or even midges. Roger Quote Link to post Share on other sites
Peter Cobbold Posted April 25, 2012 Report Share Posted April 25, 2012 Hi Peter, if only. I was in the middle of a 2 week Scots tour. There may have been water in the tank or even midges. Roger They keep the best stuff for themselves! Quote Link to post Share on other sites
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