MCM 7.4 oil

[lconove]

Hello! Seasons upon us and I have a question! Just picked up a new to me 1989 mach 1 condor in great shape. It has a 454 in it that was rebuilt 7 years ago with less than 400 hours on it. Runs great. The owner was running 5w-40 full synthetic in it. I asked him and he had called around his motor head performance friends and they said they’d switch to 5-50 synthetic. I asked some of my friends and they said leave it full synthetic if the rebuild likely had new components put in that and that they like full synthetic and at end of year switch to the 5w-50 if this oils new (it is). Engine SN:0C609422 and it starts and stays at 40-60lbs at all times.

I read that pre 1990 to run synthetic for the zinc in the oil but let me know what you guys would do especially since the rebuild?!

Thanks!

 

[Scott Danforth]

I would run Rotella T4 15w-40 diesel oil to get the zinc. Flat tappet cams need zinc

You will be changing oil every year or 50 hours anyway. Full synthetic is not needed, won't hurt, but not needed.

 

[Chris1956]

Gee, why not run what the OEM specifies? Likely it is Quicksilver 25/40 or some other FC-W oil. Auto multivis oil in synthetic, conventional or a blend, are generally not recommended.

I am not sure why the PO went to the gearheads, as it sounds like they are auto gearheads. Or are they at least marine gear heads?

 

[lconove]

Gee, why not run what the OEM specifies? Likely it is Quicksilver 25/40 or some other FC-W oil. Auto multivis oil in synthetic, conventional or a blend, are generally not recommended.

I am not sure why the PO went to the gearheads, as it sounds like they are auto gearheads. Or are they at least marine gear heads?

Offshore racing gear heads lol-Or I’d feel the same way just resorting back to quicksilver. It’s what I’ve done in the past but I see a lot of people running different oils than the quick silver. I also didn’t realize you can put “diesel” oil in these but seems like that’s just to get past emissions on gas(but doesn’t apply to marine)

 

[Scott Danforth]

. I also didn’t realize you can put “diesel” oil in these

It's the only oil left with enough zinc

Quicksilver 20w-50 does NOT have enough zinc for a flat tappet motor

A flat tappet motor requires 1200-1500 PPM of zinc or more

Quicksilver has about 850PPM. Not enough to support a flat tappet cam

Rotella T4 15w-40 still has 1200PPM of zinc and 1100PPM of phosphorus

Know the requirements of the motor.

Original oil recommend for a 1990 MCM 7.4 was SAE 30 weight dinosaur squeezings. Not synthetic

 

[lconove]

Do you guys know what the mercury 25-50 oils zinc content is? Thinking of going this route if zinc checks out

 

[Scott Danforth]

Read the post above, I didn't post it for my health

 

[Scott06]

Do you guys know what the mercury 25-50 oils zinc content is? Thinking of going this route if zinc checks out

If you google it it comes out around 800 which is generally considered too low for flat tapped cams. You could add a zddp additive.

this is why the rotella T4 is reccomended. A lot of guys on the classic car forums I’m on use it as well For same reason.

yours would have e been speced with straight 30 wt back in the day.

 

[Lou C]

Ok first find out if the engine had flat tappets. If not & you have a roller cam no real issue with zinc. But if you have flat tappets here are some choices:
Merc/Quicksilver 25/50 syn blend, I used this and did an oil analysis & it has 1300 ppm of both Zinc & Phosphorus
Valvoline VR-1 20/50 this is about the Same as the Merc 25/50
Lucas Marine 20/50, this has a very high level of Zinc, over 2,000 ppm IIRC

You won’t find this level of zinc with Merc/QuickSilver 25/40 syn blend or conventional. Why, because they are certified as cat converter safe (most inboards or I/Os made in the last 15 years have them) and for that reason have less than 1000 ppm of both zinc & phosphorus.

Merc’s 25/50 syn blend is really for Verado outboards and they do not have cats so they can go higher on zinc & phosphorus.

On my 4.0 Jeep with flat tappets I will switch to 10/30 Valvoline VR-1. This has a bit over 1,000 ppm of both zinc & phosphorus which is what oils had when these Jeep engines were current.
Only way to know is read spec sheets or do a virgin oil analysis.

 

[Scott Danforth]

BBC didn't get roller cams until the Gen VI motors in 1996.

So the OP's 1990 Mk IV motor is a flat tappet motor

 

[Lou C]

That’s what I thought
So he’s got some good choices. The VR-1 is a bargain like half the price of the Merc 25/50 syn blend, that’s what I’d use and will probably switch to when I use up the Merc oil I have