Oil viscosity
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Senior User
Joined: Mar 2002
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Oil viscosity
Need some recommendations on the proper oil viscosity for my full sized 1994 Bronco. 351 engine, 145,000 miles and I live in Fl. Bronco is not driven much, kind of like a garage queen. Getting hot already down here, so want to be sure I use the correct weight. Guy at auto parts store wanted to sell me some Valvoline Max Life (High Mileage) 20W-50. To me, that was a little thick. This Bronco is not high revved or used off-road, heavy pulling, etc. Help me out on this guys. Basically a Home Depot/Lowe's vehicle. You get the idea. Your opinions are valued.
Cargo Master
Joined: Apr 2010
Posts: 2,936
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From: Acworth, GA
20w-50 is really, really thick. I would go 5w-30, 10w-30, or 10w-40. I've been using 5w-30 in mine for a really long time. I tried using the 20w-50, and the engine developed a lifter tick, especially on start-up. I went to the 5w-30 so it would flow better at start-up, and haven't been disappointed yet.
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deadeyedevon: Thanks for the reply, but not sure if I know the answer. Guess someone could say both. Thin when the engine is cool, thick when hot. Do have a minor rear main seal leak, so perhaps the thicker blend would help. My concern is it to thick?? What would be your recommendation??
Fleet Mechanic
Joined: Dec 2009
Posts: 1,620
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From: jus south of nuts
yup, just seeping thru the rear main a little bit. on my last oil change i put in a bottle of barrs rear main sealer, ive gotta drive it around for a bit to see if it helped.
I would run 10w-30
I would run 10w-30
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Grubbworm and deadeyedevon: Thanks for the replies. Had a feeling the guys recommendation of 20-50 was not right. Gonna follow your suggestions and stick with the weights you all recommeded. Appreciate !!
Laughing Gas
Joined: Jan 2011
Posts: 763
Likes: 19
From: MA
Ok well I dont mean to hijack, but my oil pan does leak should I go to heavier oil then? If so how thick?
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Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
if your oil pan leaks first try to sinch down the bolts. not to tight though as you could make things works. start in the middle and criss cross to either end. if that doesnt work install a new gasket.
I would run a 10w30 or 10w40. Lifter tick at startup is generally from running a crappy filter like FRAM. also run a wix, purolator or motorcraft filter. on a newer motor 5w-30 would be ok since the tolerances are really good. anything with 80k miles or more should stick to 10w30 or 40.
I would run a 10w30 or 10w40. Lifter tick at startup is generally from running a crappy filter like FRAM. also run a wix, purolator or motorcraft filter. on a newer motor 5w-30 would be ok since the tolerances are really good. anything with 80k miles or more should stick to 10w30 or 40.
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Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Conventional oils with multiple viscosity ratings change viscosity as they heat up and move around. 10w 30 is relatively thin when its cold and thickens to its 30w once it is at full operating temperature. All multi-vis lubricants can be looked at this way. 20W 50 starts out thicker than 10w 30 and gets very thick and heavy once its warms up. The reason for utilizing multi-vis oil is to aid in oil distribution while the engine is cold and dry and then keep it suspended up in the moving parts once the engine has warmed up.
That may be a lot of basics and common knowledge for some folks but by way of explanation, it allows those who might not know this read and learn without having to ask.
That may be a lot of basics and common knowledge for some folks but by way of explanation, it allows those who might not know this read and learn without having to ask.
The Southernmost Mod
Joined: Dec 2004
Posts: 6,902
Likes: 21
From: Caracas, Venezuela
20w50 is a high viscosity oil, recommended for engines working in harsh and hot climates. Here in Venezuela the factory specced oil for my truck's 302 was 15w40. Once the engine has reached a high mileage (100,000 miles), moving to a higher viscosity oil is recommended, it will prevent/stop leaks and raise the oil pressure.
By the way, the numbers in the oil relate to their viscosity: i.e. in a 15w40 15 would be the viscosity value at engine start-up and 40 would be the viscosity at engine operation temp. once it has warmed up.
P.S.: You think 20w50 is thick? try looking at some differential gear oils, those values are crazy (i just used 85w140 while replacing the oil on my rear diff.), that stuff is so thick you have to WAIT for it to go down... It took me about 10 minutes or more just to empty 2 bottles on the differential...
By the way, the numbers in the oil relate to their viscosity: i.e. in a 15w40 15 would be the viscosity value at engine start-up and 40 would be the viscosity at engine operation temp. once it has warmed up.
P.S.: You think 20w50 is thick? try looking at some differential gear oils, those values are crazy (i just used 85w140 while replacing the oil on my rear diff.), that stuff is so thick you have to WAIT for it to go down... It took me about 10 minutes or more just to empty 2 bottles on the differential...
Posting Guru
Joined: Apr 2005
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From: Longview, TX
I studied and tested viscossities at 105 degrees and decided the first number is extremely important. 10W takes about 20 minutes of highway before the idle pressure drops into the 20's. Start up flow through the galleries is where you want it. Not dumped back into the pan. 10W-30 is my choice because I can not find Mobil Clean High Milage in 5W-30. Uses 1/2 quart 5,000 mile changes, only 194,000 miles. Ford recommends 5W-30 in yours also.
Post Fiend
Joined: Nov 2011
Posts: 8,908
Likes: 1
From: Algona, Washington
I used 10-40 in my truck cause i got a small leak, this has helped a bit but i haven't tried tightening the bolts yet. 20-50 is too high even for my 400. As for you guys doing gear oil, my neighbor taught me to put the bottles in a bucket of hot water to lighten it a bit before dribbling it in. Since i have only put gear oil in once (t-case) i can't say how well it worked but it definitely was slow going and it was even slower before i realized the tip of the cap had to be chopped before anything would flow out 
once i figured that out i also had to find a bigger spare vacuum hose cause the one i had from my air filter housing was too small.
once i figured that out i also had to find a bigger spare vacuum hose cause the one i had from my air filter housing was too small.