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What type of oil to run

FordF350Baby

95 F350 w/ 460
184
0
Maine
I am changing the oil in 3 of my parents vehicles all are Fords and all have over 100,000 miles. I want to know if I should put in a high mileage fluid oppose to a synthetic fluid, here are the vehicles and their mileage:

1998 Lincoln Navigator 5.4 L: 125,000mi

1999 Ford F150 4.6L: 120,000mi

2001 Ford Windstar: 183,000mi

All three of the motors run strong and none of them consume oil surprisingly, they have been well maintained and have had appropriated oil change intervals. Anyway, I wanted to see what you guys think I should start putting in their engines for them because I will be doing their oil changes from here on out and would like to stick to a brand and type of oil. What do you guys suggest, thanks.
 
Ive always used Castrol GTX. 2 Cars above 150,000, 2 cars above 100,000, and one newer vehicle. So... Castrol ftw.
 

Skandocious

Post Whores Make Me Sick
19,076
655
California
Just use whatever they've been getting. If they're getting synthetic now, then stick with synthetic (Mobil 1 is good stuff). If they're getting dino, give 'em dino (I use Castrol GTX).

It's generally not good to switch to synthetic at high mileage because it can bring new leaks to fruition. I tried switching to synthetic and my slightly dripping rear main started leaking like a sieve. Had to switch back to GTX.
 

FordF350Baby

95 F350 w/ 460
184
0
Maine
Good points, problem is I dont really know what they have been running its been between conventional to synthetic to high mileage. you bring up a concern for me, I had gotten my rear main seal replaced a few months ago on my truck, yet the bellhousing and transmission pan always have some motor oil on it, is that because i run synthetic?
 

Skandocious

Post Whores Make Me Sick
19,076
655
California
Could be. You're sure it's engine oil? If so it could also be leaking down frm higher up on the engine. Often times you can get leaks up higher that look like a rear main down below.

It's pretty strange if your getting oil on the trans pan. That'd have to be a lot of oil. Generally the rear main only leaks enough to keep the bellhousing damp.
 

FordF350Baby

95 F350 w/ 460
184
0
Maine
Hmm, I want to take some pictures to post. It use to be real bad b4 the rear main seal job, now its minimal but its always wet after i dry it. Its also wet around the bottom of the motor oil pan drain plug.
 

Skandocious

Post Whores Make Me Sick
19,076
655
California
Generally a leaking rear main won't send oil forward to the drain plug. Are you sure it's not seeping at the drain plug or the pan gasket?
 

FordF350Baby

95 F350 w/ 460
184
0
Maine
Hmm good point, it may be a warn drain plug in that case, and the pan on this thing is very aged, and needs replacing for sure, I will investigate more in the morning, I would sleep better knowing that i didn't pay for a rear main seal job that didn't stop the leak.
 

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