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MG MGB GT V8 Factory Originals Technical - Dammit have I screwed this up?

I recently purchased a V8 and the first thing I did was change the oil (10w40). Now the PO is back from vacation and tells me he'd always used Mobil 1 in the car. I've driven it about 2K miles already on the 10w40. Something tells me I have committed a horrible screw-up on a pristine Rover v8 motor. Is this so? Is there anything I can do at this point to correct the problem?

Drain every last drop of the non-synthetic, then refill with Mobil 1 (you could consider using a flushing oil between, to be double sure of removing all the existing)
David Smith

What's wrong with conventional oils? Yes, synthetics are better at holding their viscosity and give less friction. Nothing says you have to use synthetics. It's usually for people who want to pay a premium to be 'nicer' to their engines. If you want to change to synthetic, just wait until your next change.

Michael Hartwig


Provided it has not been abused, I doubt if any harm has been done to your pristine V8. In fact, it could even be beneficial if by pristine you mean the engine is still new (following rebuild?) and has not yet completed "running-in" or "breaking-in" as I think you call it over there.

Apparently, IIRC, fully synthetic oils are to be avoided in new or rebuilt engines to allow time for "breaking-in". Thereafter, synthetics become beneficial.

Both David's and Michael's advice is good. Change now if you prefer or delay and use a good engine oil flush when the next oil change is due.

Happy V8 motoring.


John McFeely


Any oil is good oil as long as it's changed on a regular basis.


my 89 ford taurus sho which has 166000 miles on it with most of the oil changes from day 1, 2 quarts of mobil 1 or syntec and 3 quarts of generic 10-30. Engine runs great, low oil use etc. You can buy from virtually every mfg besides mobil a blend oil that is part synthetic and part cooked and aged algae. All of the synthetics say on the label that they are compatible with all conventional motor oils. In the old days synthetic oils didn't expand rubber seals like petroleum oil, changing oils could cause seal leakage. Now synthetic and regular oil are very similiar in that effect. In the old days a conventional motor oil wasn't as good keeping the carbon in suspension and permitted glazing. You put a synthetic oil in and it could break loose the carbon sediments and even eventually some of the glazing and cause problems with oil passages, filters etc. Nowadays you tear down an engine using conventional oil and it looks as clean inside as it did leaving the factory. No problem switching oils. Synthetic has two advantages: 1 it is a more stable formula and will keep its characteristics longer than conventional oil, 2 it is able to tolerate temperatures up into the 400 f range without failure, some 100 degrees higher than regular oil. Great for upper cylinder lubrication and valve stem lubrication. Put one quart of synthetic in with ordinary oil, change your oil and filter every 3 to 5k miles and you've got the best of both worlds. I know this sounds awful loose and casual, but I've been doing this on cars since the late '70s and I haven't seen anything in any of my vehicles suggesting any lubrication inadequacy. I don't buy the, use synthetic and keep the dirt circulating in the engine for an extended 20,000 mile oil change.
Barry Parkinson

Do not worry. I run my B on Castrol Syntec all the time except when it is breaking in a new engine. My other car (the one that runs ) is a a Miata that gets non synthetic in summer months and synthetic in winter. The synthetic is esier to crank in the winter. Ten years and 103k miles later all is well.


I purchased a new 1978 Caprice Classic 28 years ago and after only 500 miles I switched to Mobil 1 and used it religously after that. I sold it in 1995 (17 years) with 272K miles on it (Yes, I'm a maintenance fanatic). The compression was still within engineering tolerances, although I must point out that I had had the valves and their seats reground at 148K miles. The stuff doesn't thin out at high operating temperatures and doesn't thicken up even during the coldest winter nights. The hydraulic lifters would pump up almost instantaneously no matter how cold it was. I've been using it in all my cars ever since. Great stuff. You can mix it with conventional oils, too. Just change the oil and the oil filter every 3K miles and you'll be a convert, too. Cheaper than rebuilding your engine, that's for sure.
Steve S.

'76 datsun 280Z with 314k miles before swaping a V-8 in it. My original motor gave life to a dead Z 3 years ago and is still running well

SYNTEC 10w-50

This thread was discussed between 27/10/2000 and 09/11/2000

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