Anyone using semi synthetic engine oil?

[Dunhookin]

My 1850 is having plenty of TLC, valve seats, coolant flush, auto gearbox fluid change, new brake master cylinder and more.

I'm just wondering whether anyone on here has used semi-synthetic oil? I have 3 other cars that take this grade and recently got a great deal on 25 litres of it.

Any experience or informed advise would be most welcome

Thank you

[cliftyhanger]

Semi of fully synthetics are fine, in fact way better oils (as long as the sump isn't full of sludge)
However, the issue is the grade of the oil. You don't want to be putting 5-30 oil in there. I would hesitate on a 10-40, ideally you want a 20-50, or 20-60. I am uncertain if these engines require a high ZDDP content either.
I have millers CSS 20-60 in mine, holds oil pressure brilliantly, and doesn't go black, even change colour much after a 48hr, almost non-stop drive of 2000miles.

[soe8m]

Semi you can throw in but full synthetic has a big BUT:

Fully synthetic has different dopes and one of them is keeping the engine clean of muck on the inside. When your engine had mineral oil all it's life there's a lot of contamination/residu's in the inside. A half inch thick greasy layer in the sump pan mostly and the walls and parts have a black residu cooked on. Using synthetic oil in a "mineral" or unknown history engine this does dissolve in the synthetic oil because that want's to clean your engine. All this old residu's will clogg the oilway's and makeing the actual lubrication less and less.

Synthetic oil with the correct viscosity is way better dan the less dopier mineral but only in clean engines.

Jeroen

[cliftyhanger]

Semi you can throw in but full synthetic has a big BUT:

Fully synthetic has different dopes and one of them is keeping the engine clean of muck on the inside. When your engine had mineral oil all it's life there's a lot of contamination/residu's in the inside. A half inch thick greasy layer in the sump pan mostly and the walls and parts have a black residu cooked on. Using synthetic oil in a "mineral" or unknown history engine this does dissolve in the synthetic oil because that want's to clean your engine. All this old residu's will clogg the oilway's and makeing the actual lubrication less and less.

Synthetic oil with the correct viscosity is way better dan the less dopier mineral but only in clean engines.

Jeroen

Jeroen, do these engines need high levels of ZDDP? Or how about sprints?
Thanks.

[Dunhookin]

Thanks for the responses fellas.

Clifty's point about not going too thin with stuff like 5W30 is valid, some ultra modern oils are at 00W20 viscosity - incredible. I remember way back in the 'good ol' days' - 1981/82 a mate and I both had 1972 Dolomite 1850s. A new oil was being marketed by BP - at that time - called VF7, especially noticeable as it was 10W30 grade - in an age when we were all using 20W50.

My mate and I, debated using VF7, BP was making significant claims as to its efficiency, 'better for your engine' - especially at cold starts etc. Both of us were - and still are, regular oil changers (every 3,000 miles usually) we both decided we would try it. His car went first as its oil change was due and it had an oil pressure gauge, so we could keep an eye on any changes in oil pressure.

There was no discernible change in oil pressure - and the car didn't mind running with VF7 at all. I used it in my 1850 and continued to use it for the time I had it - and then used it in the Sprint I had next. My mate used it in his 1850 thereafter and in the his next 1850 which he had for a long time, taking it north of 120,000 miles without any problems

My 1850 engine will be clean inside as it has done at most 2,500 - 3,000 miles since it was stripped for new bearings etc. With all this in mind, I feel comfortable with giving my Dolomite 10W40 semi synthetic oil at the oil change I'm about to do

[soe8m]

I use 10w50 or 10w60 synthetic. You are right about the thinner oil being better at cold starts. It takes a few seconds, about 10 when the oil reaches the head and camshaft and a 10 grade is better than the good old 20. The 40 at hot can be too thin. Parts are designed for a certain viscosity like the oilpump. When there is some wear it adds up and then a 50 would be better.

There's no need for zddp in the slant 4 engines.

Jeroen

[Manta]

Looking at my 1977 1850 Manual, it says 20-50 for uk
But if you look at the overseas recommendations, it gives the temperature range and the recommended oils for this.
For example 10-40 would be good for -20 to anything over +20
20-50 on the other hand is from 0 to anything above +20
In previous manuals it’s not set out as clear as this.

[dursley92]

Looking at my 1977 1850 Manual, it says 20-50 for uk
But if you look at the overseas recommendations, it gives the temperature range and the recommended oils for this.
For example 10-40 would be good for -20 to anything over +20
20-50 on the other hand is from 0 to anything above +20
In previous manuals it’s not set out as clear as this.

The synthetics hadn't really been introduced back in 1977 so weren't an option.

[Manta]

Looking at my 1977 1850 Manual, it says 20-50 for uk
But if you look at the overseas recommendations, it gives the temperature range and the recommended oils for this.
For example 10-40 would be good for -20 to anything over +20
20-50 on the other hand is from 0 to anything above +20
In previous manuals it’s not set out as clear as this.

The synthetics hadn't really been introduced back in 1977 so weren't an option.

Fair point, I was more referring to the question on viscosity,