Jaguar XJ6 4.2 S1
John calls in the forensics, fearful that a costly engine rebuild might soon be on the cards
1971 JAGUAR XJ6 SERIES 1 4.2
Have you ever wanted to know what is going on inside your engine? Not the generic suck-squeeze-bang-blow cycle, but what’s going on in your particular engine? Yes? Well, now you can.
I’ve recently had three engines tested by My
Oil Doctor (myoildoctor. co.uk), which has developed a service for classic car owners that costs £30 per oil sample analysed. The process is simple, with a warm but not boiling-hot engine (so the oil is thin enough to be moved) you place a thin nylon tube into the dipstick hole and draw a small amount of oil into a syringe. Once you have a full syringe, you squirt it into a bottle and pop it in the post. A report comes back via email around ten days later.
The Jag’s engine worries me a little because it was stood for some years until I bought it two years ago. Also, I haven’t managed to get the auto choke to stay off – it will suddenly lose power and start running rich. It’s coming off, but I was worried this super-rich running and consequent
dilution of the oil with petrol may’ve done some damage.
The result, on the Valvoline 20/50 that the car has been using for about 11 months and 2500 miles, wasn’t as bad as I’d feared, but could have been better.
The test picked up on the high lead content from the Millers additive I use, but the calcium was 50 per cent higher than ideal at 3840ppm, which means that the oil type has changed at some point. However, calcium is in almost every engine oil because calcium compounds are used as detergents/ dispersants and give oil its alkalinity. Classic car oils often have higher levels of calcium and it’s not usually detrimental.
The level of tin was 6ppm when the desired figure is 3ppm, which means some bearing wear may be ongoing. The chrome was 6.5ppm (it should be less than 5ppm), which means some blow by oil consumption on the piston rings is probably occurring as well. The zinc and magnesium was high as well due to the oil type change, but the iron was high at 294ppm ( less than 50 is desirable), indicating some wear in the main bearings or crank.
So, not a death rattle yet, but a sign that rings and shells may well be needed at some point, which I suppose is to be expected on an XK engine that’s done almost 70,000 miles and never been taken apart.
It also showed a higher than desired silicone reading of 16ppm – common in engines that have been stood due to dirt ingress – so we’ll see if this has reduced when I do another oil test in two oil changes’ time. The viscosity reading was double what it’s supposed to be, which can indicate the wrong oil being used, water ingress or past overheating, none of which are applicable as far as I can tell, but is also more likely be an issue with mineral-based classic car oils, so again, this is something to look at when I re-test it.
The last test involves the oil being scanned by a magnetic robot to find the amount of metallic particles and is measured in PQI (Particle Quantity Index). Once again, this was high, which indicates bearing wear. However, the compression readings I took a while back were good, wet and dry, and the engine runs smoothly (auto choke notwithstanding) and produces what feels like good power, so it won’t be coming apart yet.
And if £30 sounds a lot, look at it this way – it’s much cheaper than a full engine rebuild…