Can i use 5W20 oil in my 1991, 4.9l f-150? Will it cause damage?

Asked by Apr 16, 2015 at 06:36 PM about the 1991 Ford F-150 XLT Lariat LB

Question type: Maintenance & Repair

I have a 1991 f-150 long bed, which I rarely drive...trips to the dump, etc.)
Without paying much attention, I changed  my oil.  I had used 10W40 in it last time
I had a 5 quart jug of Valvoline Max-Life 5W20 in my toolbox for a long time, and didn't think to check the viscosity...now I'm wondering if I need to change it AGAIN!

3 Answers

229,055

Since you rarely drive it, I would think it would be fine, when you have to add or change it next time just add 10W-40 to keep the level up.

1 out of 1 people think this is helpful.
17,230

The two numbers associated with the oils refers to their viscosity. (the thickness of the oil) The lower the number the less thick it is. The first number (5W) refers to it's properties in cold weather 5 is less thick than 10, so in warm weather you should be ok. The second number refers to the viscosity of the oil when hot, engine running. 20 is thinner than 40 and flows much easier. You engine is much older and no doubt has some wear on it. You may see a little smoke from the tailpipe using 5W20 as thinner oil may slip past the rings and cylinder wall and be turned, and a slightly noticeable reduction in power. (loss of compression) with thinner oils. 5W20 oils were only developed within the last 5 years or so and are called energy conserving oils. Engine components on newer engines are machined to much closer tolerances, requiring thinner oi,l to increase MPG (cafe figures)

17,230

correction "will be burned."

Your Answer

Add photo

Related Questions

  • rough idle while in gear 6 answers

    I bought a 94 ford with the straight 6 (4.9L) apparently the guy had been chasing the check engine light that was on. it has all new plugs, plug wires, cap, and catalytic converter. Now I found out t...

    1994 Ford F-150 XL SB

    -

    Maintenance & Repair

  • forgot to put oil in... 9 answers

    so im doing an oil change today on my 2004 ford f150, and i got distracted at one point, and i ran the truck with no oil in the engine. i shut it off because i heard a somewhat loud knocking noise. i...

    2004 Ford F-150

    -

    Maintenance & Repair

  • 1988 F-150, 302 eng, A/C will not accept freon, compressor kick 0n and off. What do I do? 14 answers

    My F-150 will not accept Freon, compressor kicks on and off. I have the adapter hooked up to the large fitting by the A/C dryer. The A/C switch is on and the blower on high.

    1988 Ford F-150

    -

    Maintenance & Repair

  • I have a 2007 f-150 that just started one day makeing a nosie from under the truck. 1 answer

    The nosie dont happen all the time,so i dont no if something is just starting to go or what. the nosie started about 2 weeks ago its a grinding howling nosie sounds just loud as hell from under the tr...

    Ford F-150

    -

    Maintenance & Repair

  • can damage be caused by overfilling oil? 4 answers

    This more of a follow up question about the same ford escort with the damaged #4 sparkplug. I decided not to make repair on this car (too expensive) due to its value. I had loaned this car to my daug...

    1999 Ford Escort 4 Dr LX Sedan

    -

    Maintenance & Repair

F-150

Looking for a Used F-150 in your area?

CarGurus has 209,709 nationwide F-150 listings starting at $895.

ZIP:

Search Ford F-150 Questions

Ford F-150 Experts

#1 OJ
OJ
Reputation 7,220
#2 dandyoun
dandyoun
Reputation 4,270
#3 tennisshoes
tennisshoes
Reputation 2,600
View All

Related Models For Sale

Used GMC Sierra 1500
896 Great Deals out of 64,573 listings starting at $1,500
Used Ford Mustang
332 Great Deals out of 45,523 listings starting at $2,000
Used Ford F-250
478 listings starting at $3,975
Used Ford Explorer
758 Great Deals out of 74,253 listings starting at $750
Used Ford Ranger
189 Great Deals out of 6,216 listings starting at $1,000

Used Cars For Sale

2017 Ford F-150 For Sale
4 Great Deals out of 118,021 listings starting at $18,165
2016 Ford F-150 For Sale
165 Great Deals out of 28,375 listings starting at $17,877
2015 Ford F-150 For Sale
172 Great Deals out of 7,279 listings starting at $11,600
2014 Ford F-150 For Sale
429 Great Deals out of 12,262 listings starting at $9,995