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Is 20w-50 Oil in a '98 4.6 a good idea?


Old 01-06-2004, 01:08 PM
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Question Is 20w-50 Oil in a '98 4.6 a good idea?

I have a 1998 Expedition with a 4.6 it has had 5w-30 or 10w-30 in it throughout its 107k miles. It uses about 1 qt per 1000 miles now. I am thinking about switching to Castrol 20w-50 (which I have used in most of my vehicles in the past) but am wondering if it will affect the seals, or anything else in a bad way. I don't understand why Ford recommends such a thin oil.

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Old 01-06-2004, 02:04 PM
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We use 20-50 in our '92 grand marquis with the 4.6, but thats because it burns throgh 10-30 in no time.

I think 1 qt per 1000 miles is "acceptable" according to Ford.

Is the oil being burned, or is there a leak?
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Old 01-06-2004, 08:57 PM
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Switching to a think 20w50 oil will reduce your oil consumption, but it's ability to flow where it needs to flow and lubricate where it needs to lubracate won't be as good. In the bearings it will heat up, shear down, and sludge up your engine making things worse.

You are much better off to clean up the rings, seals, and oil pasages with an Auto-RX treatment and keep running the same oil you have been 10w-30, adding as you need to.

Some engines burn oil because a lower ring in the ring pack gets stuck, and the grooves all line up in a row. When this happens oil just flows along the ring grooves.

If it's an older engine design you can get by with something like Delvac 1 5w-40, but not a 98 Triton. It will work, but in the long run it's not better.

Last edited by greencrew; 01-06-2004 at 09:00 PM.
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Old 01-07-2004, 07:59 AM
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If you switch to 20W50 you will loose major MPG. Not to mention all that Greencrew said. In short, not a good idea.

If oil consumption is an issue, try a synthetic like Mobil 1, Red Line, Amsoil. After a few oil change intervals, the synthetic's cleaning agents and friction modifiers should benifit your situation.
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Old 01-07-2004, 09:49 AM
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20w50 won't hurt your seals or anything , but check for oil leaks first . Ford uses such a thin oil because since the late 80's they cut thier eng. bearing clearances down,and refined thier eng. allowing the eng. to make it to 250 000 -300000 km before wearing out.

I use syn. 5w30 and at 240 000km I burn about 1/3 qrt per 1000 miles .in my 4.6l v8
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Old 01-08-2004, 04:19 AM
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20W50 is not recomended in a 4.6L or 5.4L. That is one heck of a heavy oil for use in a newer engine. Use it at your own risk. 20W50 will not flow in areas of extreme cold, being that we are in the winter season. If you had a 5.0L mustang engine, maybe in the heat of summer you'd use it, but the clearances of a modular engine aren't as forgiving. In in the late 80s and early 90's Ford suggested 10W30 for use in their Crown Vics. In 1997 they started using 5W30, and in 2001, they suggested 5W20. These engines have NEVER specified a 50 weight oil, and unless your engine is worn the heck out, you will not benifit from 20W50.

PS- I am not aware of the bearing clearances you are refering to. Maybe you can post a 4.6L engine schematic from the early 90s compared to one today. All the Blue Oval master mechanics that I have talked to can't specify which clearances changed from 1996 to 1997, nor the ones from 2000 to 2001. Please shed some light on this issue.

Last edited by mf150; 01-08-2004 at 04:23 AM.
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