Anyone tried Synchromesh in the manual transmission? | Ford Explorer Forums - Serious Explorations

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Anyone tried Synchromesh in the manual transmission?


Explorer Addict
October 22, 2006
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City, State
Huntington Beach, CA
Year, Model & Trim Level
98 XLT, OHV, 4D, 4x4, 5M
I know it calls for Mercon fluid, but I've heard that a manual transmission lubricant (such as Amsoil, Pennzoil, or GM synchromesh) provides better wear protection because its slightly thicker and more robust. Any comments?

I have Amsoil synchromesh in mine and its somewhat crude when cold, but feels good once its hot. My prior vehicle, a 2000 Sport, had both synthetic Mercon at one point and Redline MTL at another point, both feeling roughly similar. The ATF was better when cold but rougher when hot, when compared to the Redline fluid. I assume this means the ATF was becoming too thin with temperature.

Thanks all.

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Thicker oil doesn't protect better. You need the lighter ATF for these transmissions to ensure proper lubrication. Ford has what we call "honey oil" which is the OEM equivalent of that synchromesh oil, and if Ford believed you needed it, they would recommend it, because it costs a lot more to buy that from ford than it does to buy ATF. The LIGHTER oil protects better in this case. You should also get better mileage using the ATF.

Well, my logic was that the clearances in the bearings and synchros have relaxed some since new since the trans has over 200,000 miles, and that the synchromesh additives would help the synchros since they've obviously seen some wear.

Nah, you should generally stick with the same viscosity of oil for the life of the transmission and there isn't really anything about the synchros in this transmission that synchromesh is good for, the ones that need it use different alloys. Like I said, you are better off sticking with the ATF.

I did some research and found that Amsoil MTL is slightly heavier than ATF, but not that much: 9.6 cst @ 100 C compared to 7.5 cst @ 100 C for most ATFs. However, I tend to agree that I should stick to what was recommended at least in terms of viscosity. I just ordered some Redline D4 ATF which is meant to replace Mercon V and will report results when I change it out.

Yeah, I think the MTL is around 50 weight whereas ATF is a 30 weight oil.

Well, I put Redline D4 ATF in my tranny. Cold shiftability is better, hot shiftability is about the same. The gearbox is still fairly crude but worth the $33.

The M5OD in my 2000 Sport was pretty crude when I got it at 94k miles, I guess I can't expect miracles at 203k on my current rig.

Amazon has D4 ATF for $11 a quart with free shipping.