Latest Reader Question (October 10, 2017)

Here’s the latest reader question, along with my reply:

Robs asks: When driving my old farm truck I notice the transmission (manual) runs hot. Dumb question but, do I get a transmission flush or change of fluids? Assuming you will say yes, my next question is then how often should this occur. Note – I am not a total idiot, I keep my oil regularly changed; I just have never known what the rule of thumb for transmissions is.

My reply: Well, first order of business is to establish that it is, in fact, running hot. Then find out why.

Manual-equipped cars generally do not have a gauge (or light) to tell you that the gearbox is running hot. You’ll want to first get a value for “hot” (vs. normal operating range) and then use an infrared temp gun to check the actual temp of your transmission to determine whether it is, in fact, running hot. Which it ought not to be unless the lube level is low or there is a mechanical problem increasing friction internally.

So, begin by checking the lube level. Most manuals don’t have a dipstick; they have two plugs – a drain plug near the bottom of the case and a fill plug up higher. Usually, “full” is determined by a small trickle of oil coming out of the fill plug when it is removed. If no lube comes out when it is removed, the level is low. Add until you get that little drip/trickle – then re-install the fill plug.

If the fluid is very low  – or looks dirty – I’d go ahead and change (not flush) it. No need to flush a manual because it has no cooler/lines/torque converter, as an automatic does.

Simply removing the drain plug will get almost all the old lube out.

Before you remove the drain plug, remove the fill plug – to facilitate drainage. Place a catch pan underneath the transmission and remove the drain plug. Let it drain thoroughly, then refill. Be sure to use the right weight of lube (see your owner’s manual) and be aware that some manuals take automatic transmission fluid (ATF).

As far as how often: The general interval is once every 50,000-75,000 miles or so – but this varies by manufacturer. However, no harm will come from changing the lube once every 40,000 miles or so (which is what I do) and by doing this, you’ll always have fresh lube in the thing and (my experience) the transmission will shift more smoothly and last longer, too.

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