I've had my 96 for about 3 years now and I've always used 10w40 cause that's what everyone said to use with the Windsor. I was lookin at my owners manual the other day and it says to use 5w30. What do you guys think I should use and will the 10w40 hurt anything? Thanks.

 

Do you have any oil leaks or does it smoke?

 

It's going to depend on what the 10w-40 is and how the oil makes the spread. The old 10w-40 was loaded with polymers to make the spread. They also created tons of sludge. As far as the viscosity goes, you're not hurting anything.....anymore. But I'd be more concerned with sludging issues than anything. If you can look into a valve cover and see if it is sludged or pull a valve cover, you probably will be doing yourself a favor.You will also do yourself a favor by using something else, like a 5w-30 in a high mileage oil.

 

I've looked in the valve cover before and it still looks like new in there.

It doesn't leak or smoke. Well, there's a small hole in the oil pan that I've patched but it still seeps out.

 

As far as viscocity goes he's at around 100 at startup with 10w40 dino oil and 75 with syn. 5w40 syn is around 55 and 0w40 is around 40 at startup. They all have the same viscocity when hot and running at 212 degrees which around 10. When 90% of engine wear is at startup you want the lowest amount friction you can get which is 0w.

Read my post above and get a high quality syn like Mobile 1 or Redline with a high quality filter such as Mobile 1, Wix, etc. I'd go with 0w30 or 0w40 with the mileage you have, but an oil analysis will give the most accurate data on what you should use.

 

185,000 on my 97 4.6L- use only 5W30 Mobil1. Uses 1/2 qt. in 4000 miles. Live in Phx, AZ

 

You can get away with 10w40 in a 351 as long as it doesn't break down and sludge on you. However, 5w30 or 10w30 would be preferred.

 

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Thanks guys! I guess my next oil change I'll use 5w30. One more question. Would using 10w40 make the engine kind of sluggish?