What oil viscosity is best for my 70 351C? It has 63k miles on it, but just got new main and rod bearings, timing set, and high volume oil pump while out for new freeze plugs. Rings and cylinder walls still looked great, and there was very little carbon build up. Oil pressure on a mechanical gauge runs 75 psi at cold start, 55 psi hot idling in drive, and 70 psi hot at 2000 rpm. I have been running 5w-30 but don’t ever start the car below 50 deg. So I am thinking 10w-30 might be a better choice, and do I need to add the zinc additive for the cam/lifters?
You should just buy oil that has the required amount of ZDDP in it. There are many brands that will do fine. My rule is to get something that is available everywhere. So I use Valvoline Racing oil. Any Wal - Mart has it, as do most auto part stores. Your old flat tappet performance engine from the 1970’s needs it all the time to prevent damage.
Your glove box book has recommended oil types for various temperatures. 5W-30 is not one of the listed oils. 10W-30 is a typical winter oil grade.
Thanks Royce
5w-30 actually is called for in the 1970 Cougar owners manual for temps consistently below 32 deg. My mechanic likes the thinner oil in the 351C because along with high volume oil pump, it is easier to get more oil through the 351C’s oil distribution system limitations. But of course I am operating consistently above 32 deg C, and am often over 60 mph. I like the common availability of Valvoline Racing oil with ZDDP, and will go with 10w-30.
Has anyone researched using Diesel oils rated for gas engine usage to take advantage of their higher zinc content?
An oil rated for diesel will get the inside of the engine clean with out put being to harsh…?
Some of the diesel oils has the zinc taken out of it. So, do your research before using. I run Valvoline VR1 10w30 like others have said, widely available everywhere even online if you can’t get it locally.
Shell Rotella T4 15w-40 is an old standby for classics with flat tappet cams. It’s a diesel oil marketed towards big rigs, and it has the proper levels of ZDDP and other additives to keep our cams safe. It’s also available everywhere, and it’s cost effective. As for the detergent mix being too harsh for our engines, any talk of stuff like that is an old wives tale; no detergent in any modern oil is going to harm your engine.
What’s always more important than the type of oil you use (as long as you are using one with enough ZDDP) is that you change it at least once a year regardless of mileage. Any oil that sits around will start oxidizing and eventually lose its effectiveness regardless of mileage.
My engine builder recommended that I use Honda GR4 10w-40 for my new 351w. It’s got enough ZDDP and other performance additives to keep my flat tappets safe, and he is of the opinion that motorcycle oils are even better for high pressure and sheering applications because they are designed with the knowledge that motorcycles generally share oil between the engine and transmission. That’s part of the reason why a lot of the air cooled Porsche guys use oils marketed towards Harley’s. I haven’t heard it from anyone but him, but he has spent a lot of his life building engines for vintage racers, so I can’t imagine he doesn’t know what he’s talking about.
I’ll throw on the end here that VR-1 is also super common in the community and I’ve never heard a bad word against it, but I have never used it because the T4 Rotella is so much easier for me to find. Just please don’t use a Fram filter.
Ken
Thanks to everyone for so much good oil info! Hadn’t heard to avoid Fram filters before. I had used them for years, but now use Motorcraft FL-1A filters on my Cougar.
I think the viscosity used is somewhat determined by your bearing clearances and obviously several other things. I’ve been using Lucas Hotrod 10W30 which has ZDDP in it. I run a Hydro rollor so do not really need the zddp but run it anyway. https://lucasoil.com/products/hot-rods-classic-cars/hot-rod-classic-car-10w-30-motor-oil
My oil press is 85psi cold 35 to 40 hot idle and 60 to 70 mid rpm hot. I run a blueprinted standard oil pump and if I remember correctly 25thou rods and 20 thou crank clearances, I could be off though as its been 7 years since I built the motor and don’t have my spec sheet with me.