Engine Oil

[Glyn Ruck]

Personally I would not worry about oil pressure unless it is alarmingly low. But if you like >40psi at 3000RPM then just go up a grade as you mention. At least it is not shearing out of grade & will be providing far better protection all round. Pre S Type on earlier XK engines Jaguar used a 100lb gauge & changed to the 60lb gauge to stop people worrying about oil pressure & keep the needle approx mid gauge in normal operating conditions. You might have a slightly lazy oil pump but I doubt it. My engine also has a refurbished original oil pump. Works just fine. In fact my oil pressure runs slightly on the high side but with Covid I'm still bedding in on a monograde SAE 40. I Plastigauged every bearing in my engine so clearances are spot on.

So the message is don't worry ~ you will be getting excellent flow & protection. Feel free to tailor viscosity to your preferred range for your specific car ~ we don't know how close to blueprint all clearances are. Synthetics just have a far flatter viscosity curve than mineral oils. They thin less at hi temperature & thicken less at low temperature. Known as Viscosity Index. The good thing is that the High VI is due to better base oils & less VI improver addition that can shear. Synthetic base oils are inherently high VI. The oil will not shear due to getting too hot. It will shear due to cheap VI Improvers used in many so called classic mineral oils (the oil pump, chain drives etc. shears the polymer from long strands to short ones which lowers viscosity). If anything oil getting too hot will cause it to thicken due to oxidation & some evapourative loss. (Noack)

What is your oil consumption like? Might go up a little initially during ring belt cleaning.

I would certainly not pull the engine apart chasing ghosts. Depending on where the oilco blended the oil within the viscosity range for that grade some people might notice a slight oil pressure drop with synthetics. Many blend to the low end of the scale to improve fuel consumption. The fact that you have seen no change in oil pressure with use is exactly as expected.

[Orlando St.R]

Thanks for your reassurances and further education, Glyn. We are very fortunate to have you contributing to this forum. I probably am a bit paranoid about my oil pressure!

Oil consumption is around one pint per 400 miles, if that's the unit of measurement. Or one litre per 800 miles.

I'll keep you all posted as to how I get on.

[John Quilter]

Loads and loads of opinions and comments here about oils. Reminds me what would happen if you asked a group of women what cosmetics are best.

[cass3958]

The difference here John is instead of talking to a load of salesman trying to sell us their wares we have Glyn who is a Tribologist and therefore an expert on the topic of all thing oily.

[Orlando St.R]

I thought I'd update you all on my oil pressure experiences in 2021.

Following my previous post bemoaning low oil pressure when using Millers 10W40, in May 2021, I changed the oil and filter for Mobil 1 10W60 fully synthetic. But, on my first outing, oil pressure on the gauge again failed to reach 40psi at 3,000rpm. Time for investigation.

I took the car to The Splined Hub in Oundle and they put a mechanical gauge on to reveal that there was plenty of oil pressure! They also tested the gauge, which was fine. They suspected the sender and, sure enough, that was the culprit. "We replace loads of them", they told me.

So, now I have ample oil pressure and I'll probably try a 10W40 synthetic again next year, because it'll probably be fine.

You'd think I'd know this having replaced a faulty sender only a few years back!

[John Quilter]

Maybe I should test my gauge as well. On a recent summer trip (ambient temp 90F) the pressure on a newly rebuilt engine with crank turned and all bearings replaced, was about 35 lbs at 2600 RPM hot. Temp gauge was at about 85C. I run Castrol 20W 50. The strange thing is the oil pressure dropped about 5 PSI AFTER the overhaul. Car has about 700 miles since engine work. As was stated maybe I'm obsessing about this.

[Glyn Ruck]

Orlando. I'm so pleased you have sorted this out because I never want to appear to be giving poor advice. BTW on reading old bulletins on Terry's Jag site IIRC Heynes & Co had stated that oil pressure was fine between 35 & 45psi at 3000RPM dependent on oil viscosity used. This makes sense when they were recommending as low as old technology 20W low VI monogrades in winter. I try to give the very best advice I can & did not want to believe that your engine clearances were out. I'm trying to kill this old & erroneous nonsense that the only oil to use in these cars/XK engines is ancient technology 20W-50 low VI mineral oil that shears out of grade & Jaguar never recommended in the first place. There are real benefits to longevity of our engines in running quality Multigrade Synthetics. They are NOT too "thin" as claimed by many who simply don't understand. An SAE 10W-40 is a 40 at operating temperature. The highest viscosity Jaguar recommended in severe tropical conditions.

I would never suggest something I would not do in my own car. I Plastigauged every bearing during my engine rebuild, as mentioned before, and my oil pressure is slightly on the high side while running in on an old SF 40 monograde mineral oil & ignoring Jaguar's run in procedure that is obsolete. My sender unit is also new. But I want to run in properly prior to moving to over protective synthetics that will impede break in & could cause an oil burner due to this.

Good luck & good news!

[Glyn Ruck]

I wonder whether it is worth keeping a spare in stock at the Southern tip of Africa? I'm about to order a long list of very minor bits I need from Barratts. Little things like correct spare wheel well metal plugs, bellhousing swivel cover & copper bifurcated rivet etc. etc. That I'm still missing or have substituted rubber plugs for. Darn exchange rate is floating all over the place.

Oil pressure sensor..JPG (16.02 KiB) Viewed 2911 times

[NigelW]

I got fed up with unreliable sender units that I have replaced a few times over the many years i have owned the car so i added a Smiths mechanical guage plumbed into the main oil gallery.

[Glyn Ruck]

So you are using a capillary feed gauge Nigel? How long does it take to register peak pressure?