synthetic oil in gt-40

[walleye]

A friend owns a 96 sn with a gt-40 motor, and this spring he put mobil synthetic in the motor. Two days ago while skiing he noticed a drop in oil pressure he limped it back to shore. He took it to a buddy that works on motors and was told that the synthetic was the problem. After doing a compression check the pistons range anywhere from 125 to 90. He was told that replacing the motor was his best option. Has anyone ever came across this?

[01Ski196]

RE: synthetic oil in gt-40

I run Castol 5W-40 Synthetic in my 2001 SN with GT-40 and have never had a problem. How far of a drop in oil PSI?

[bobchris]

RE: synthetic oil in gt-40

lucus syn oil or royal purple are the only ones to even concider.

Moble 1 is the worst junk on the market

[DanielC]

RE: synthetic oil in gt-40

PCM specifically recommends conventional motor oil in marine engines. Why would you go against the engine builders recommendation? I have 1879 hours on my GT-40 using Valvoline 40 straight weight racing motor oil. While you are at it, get a Motorcraft FL1-A oil filter, do not get sucked into the hype and use Fram filters.

[MiracleDriver]

I had put synth in last season and from recommendations here I drained it and run straight 40 weight. always ran 10w30 before as per manual. its a 1990 351 with roughtly 900hrs no gt40.

we did a comp check and have 1 hole down a bit, the rest are around 120. no notice of oil pressure loss or power.

if you didn't run it for long with the synth in it I don't think that would cause the comp loss, but if he's run it a lot and at skiing speeds it could I suppose. If you have a few cylinders that are down then consider a short block replacement.

with a fresh oil change how is the oil pressure?

check it with a mechanical gauge to be sure.

[madmax]

I change my oil every spring and I have run synthetic in my 98 snob (700hrs) for about 5 years no problems. I am now running it in my 99 air. (mobil 1)

[TRBenj]

Synthetic motor oils dont contain the heavy metal additives that are necessary on flat tappet motors. Synthetic is just too slippery and doesnt stick to the metal-on-metal contact patch between the cam lobes and flat tappet lifters. The Ford 351w is a flat tappet motor- this includes the GT40. Stick with a conventional oil like Shell Rotella-T or Valvoline Racing... otherwise you are just asking for trouble.

If you dont believe me, check this article:
http://www.hotrod.com/techarticles/e...ppet_cam_tech/

The new Chevy motors have roller cams in them, so synthetic should be fine in that case.

And this isnt related, but DO NOT use synthetic in the transmission. Although synthetics are supposedly 100% compatible with other ATF's, they are just too slippery for our wet clutch transmissions. Ive spoken to SkiDIM, Correct Craft and PCM and they all say the same thing- stick with conventional Dexron/Mercon ATF. They have seen tranny failures in the 500-600 hr range when using synthetics.

[H2O]

Todays synthetic oils are not synthetic at all. They are dino oil that has been further refined to ensure that all the molecules are approximately the same size rather than a wider variety of sizes. They will not harm your engine any more than standard dino oil. What is important is the additive package in the oil and changing it at the interval recommended by the motor manufacturer.

[walleye]

Thanks for all the advice , I just talked with my buddy and hes heading to the lake with fresh oil to see how its running. At the end of next week hes going to get another compression test. hopefully he can salvage a couple hundred more hours ouy of the motor, I'll keep you imformed.

[MHayes]

Re: RE: synthetic oil in gt-40

Moble 1 is the worst junk on the market

Yeah, I guess that's why Porsche puts it in all of their new cars. :rolleyes: