10W30 synthetic in winter? | Ford Explorer Forums - Serious Explorations

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10W30 synthetic in winter?


Well-Known Member
March 3, 2001
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City, State
Regina, Saskatchewan, Canada
Year, Model & Trim Level
'94 XLT 4x4 4 Dr **sold**
Hey guys. I used to come to this site all the time when I had my Ex, but I sold it a few years ago. I have checked in occasionally over the last few years, mainly to get tips for my brother in law, who has a lifted Ranger, and just to check in on your rides.

I just bought a 84 Bronco II (2.8, 5 spd, carb'd)with high mileage(I suspect it is high, odometer says 51,000, but don't know how many times it was wrapped). Anyway, I wasn't sure when the fluids were changed last, so I changed all of them, diff's, tranny, transfer case, went to synthetic for all of them, mainly due to the benefits in cold weather (routinely gets to -40 here in winter, and synthetic makes a huge difference then). But I am holding off changing the engine to synthetic because there appears to be a slow leak coming from the front of the engine, either the crankshaft seal or the front of the oil pan. The rear seal may be leaking as well, there is old caked on oil on the bottom of the tranny, not sure if it is splash back from the front leak or a leaking rear seal. I don't want to make it worse by going to synthetic.

I usually use 5W30 all year round. Would going to a thicker 10W30 (synthetic) give me the cold weather benefits of a synthetic, but would not leak as bad as a 5W30? I would expect a synthetic 10W30 to flow alot better than a conventional 5W30 in the extreme cold, correct? Or should I just stay with regular 5W30? Would synthetic 5W30 leak too much?

And yes, I know that "just fix the leak and then go to synthetic" is a good answer, but I want to hold off doing that until I see how bad it is. If it is only going to leak a quart over an oil change, I will likely just leave it for a while.

Any advice would be appreciated. Thanks.

P.S. I am aware that there is a Bronco II forum, but there is not near the amount of activity/info there as there is here.

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I would think the 5W would be better in winter because it is thinner when its cold. After they get to operating temps, they're the same. The 10W is just a little thicker when its cold and would make starting a little harder. I would stay with the 5W.

It would be an interesting experiment, to put 5W30 dino in a freezer and 10W30 synthetic, see which flows better. I may just try it.

If I were you, I would run a 0 w 30 synthetic such as Amsoil Series 2000 oil. I run it year round in Florida.

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Amsoil is not as common here in Canada as it is in the States. I have only seen Amsoil Synthetic ATF, maybe I just need to look harder.

I really want to go to synthetic because I have seen where it is the difference between a vehicle starting or just going rrr,rrr in the winter. Just scared of the leaking seals. aldive, I have read your opinion on synthetic not causing or making leaks worse, but I have also heard anecdotal evidence stating otherwise, so I dunno. I may just wait a month or so and see how bad the leak is, if it is not bad, will go to a 0W30 or 5W30 Syn per your advice.

What is the opinion on the "high mileage" oils that are out there? Just a marketing gimmick?

Thanks for the replies.

Search the web for Amsoil dealers, they will ship to you.

Good luck.