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Change manual transmission fluid?

I have a '97 Pontiac Sunfire 2.4L with a manual transmission. The maintenance schedule in my manual says that the transmission fluid does not need changing. However, I keep hearing that I should change it anyway, so I took it to an express lube place this morning.

They said they couldn’t change it 'cause there’s no easy way to fill with new fluid.

1. Would you change the fluid (I have 104k miles on the car)?

2. How do you change it?

Never let an express lube place change your transmission fluid manual or automatic. Most manual transmissions are just topped off with gear oil. Make sure you use the proper weight for your transmission as your vehicle calls for “Synchromesh Transaxle Fluid”. It’s your call on the fluid change. I would follow the owners manual recommendation if it were me. Transmission fluid should be changed if you have a transmission problem of some type. If it’s shifting great just leave it alone.

The express lube place did you a favor. You should never go to them for anything.

I change my manual transmission oil myself. Once you find the drain plug and fill hole, you might need to buy a special funnel to reach the fill hole, and you should definitely buy a new crush washer for the drain plug. You also might need a new crush washer for the fill hole plug.

Once you know how to find these things, changing your transmission oil will be just like doing an oil change, except there is no filter to change.

If you can’t figure this out, there is no shame in getting this done at an independent mechanic’s shop. It should cost no more than $40 (before tax), but in some areas, it might cost as much as $60.

I believe you should definitely get this done, and you should consider using synthetic oil to fill the transmission if it is available in the correct viscosity.

When doing changes of this type yourself, always make sure you can loosen the fill hole plug first, before you drain the fluid.

A service manual would be helpful here…Before you start, be sure you have located both the fill and the drain…Be sure you have the CORRECT lubricant to refill the transaxle with…
It could be 90W gear oil, ATF, motor oil, or a proprietary GM lubricant…

I would not bother on a '97 changing the fluid especially if not exhibiting any problems.

Honda and other mfgs recommend changing the fluid in a manual transmission. I don’t see how it could hurt, but I would suggest spending a bit of extra money and using a GM brand fluid that is spec’d for your transmission. Have you asked a GM dealer what they would charge for a tranny fluid change?

Most manual transmissions are like rear differentials with two plugs. The one on the side of the case is where you fill it, the one on the bottom is the drain plug. Some fluids come in a plastic container with a top that is tappered to fit in the side fill hole and you squeeze the bottle to put in the fluid. When it reaches the level of the fill hole and runs out the hole, then you are filled up. There is no filter.

100,000 miles used to be a decent fluid change interval on a manual transmission. The gear oil, on an atomic level, is made of long-chain molecules that prevent wear by literally keeping the gear teeth from contacting each other. Over the thousands of miles of driving the shearing action of the gear teeth tends to chew up these long chain molecules. The fluid loses viscosity and breaks down, decreasing the ability to prevent wear.

If your manual states you don’t need to change the gear oil, that may well be because the transmission came filled with synthetic gear oil. Synthetic oils are less prone to viscosity loss through shear. So instead of being shot after 100,000 miles of driving this fluid may last 200,000 or 300,000 miles. But it can’t possibly have an infinite service life.

The folks at Pontiac probably figured that the car would be scrapped before the gear oil needed to be replaced. And that in turn may be the reason why the express lube folks said there was no easy way to change it. If there was no expectation of service, the msnufacturer may have simply not bothered to drill, tap, and plug fill and drain holes in the transmission case.

Pontiac (r.i.p.) only needs the trans to make it through the warranty period.
I changed the trans oil in my '88 Accord every 30K miles, per what the manual called for. It’s so cheap to DIY.
I plan to do the same with my '06 Matrix, even though the manual says no oil change in the 120K mi. it covers, except under ‘special operating conditions’.

If you just want to spend some money and can find a shop that will change it, then do it. But I have been driving 60 years and have NEVER changed or repaired one.

I agree with EllyEllis. In 50 years of driving manual trannies, I have never changed the fluid and never had a problem.

Did any of those transmissions use 10W-40?

EllyEllis, I thought you drove automatics. When was the last time you owned a vehicle with a manual transmission? How many miles did you put on your manual transmissions over the years?

With all due respect, 50 years ago, people didn’t expect their cars to see the 200,000 mile mark. Back then, a car with more than 100,000 miles was usually thought of as a beater. If your car’s expected lifespan is only 100,000 miles, of course there is no reason to change the manual transmission oil. However, if you want your manual transmission to see the 300,000 mile mark, changing the transmission oil every 30,000 miles is cheap insurance. When I change the oil in my manual transmission, it costs me the price of two quarts 10W-30 of oil.

Did any of those transmissions use 10W-40?

Not likely.

There’s a HUGE difference between what engine oil and transmission oil do. And there’s a similarly large difference in the type of lubricant used in each. Engine oils typically have multiple viscosity properties (i.e. 10W-40, 5W-30) with the thickest viscosity generally being no greater than 50. Gear oils (as used in manual transmissions and differentials) typically start in the 75W range (far thicker than even a 50W engine oil) and generally max out in the 90W range.

Those larger numbers for gear oils reflect a greater viscosity (thickness). This is directly related to their resistance to shear as I outlined above. Manual transmissions and differentials are designed to do one specific thing (transmit power) and so you can run a relatively thick oil and expect a relatively long (100,000 miles or more) change interval.

Running motor oil (10W30, 10W40, etc) in a transmission won’t wreck it outright, but it will require you to change out the oil far more frequently than you would if you ran a gear-specific oil. The vast majority of the motorcycles on the road today actually share the engine oil with the transmission, but these generally require an oil change interval of every 4,000 miles or so.

Bottom line: Lubricant’s don’t have an infinite life. Follow the manufacturer’s suggested change intervals. And just because you’ve gotten away with never changing the lubricant in a manual transmission or differential doesn’t mean it’s not necessary- it’s more of a reflection of how well engineered the transmission and lubricants are.

Many Japanese automakers specify 10W-40 or 10W-30.

Agree with ^…
My '93 Civic requires the tranny 10W30 changed every 2yrs/24k miles.

Old Putz, I beg to differ.

My car uses 10W-30 oil in the manual transmission.

My motorcycle has an oil change interval of 8,000 miles, in spite of the fact that the transmission and the engine use the same 10W-40 motorcycle oil.

Refer to my user name. Most of my experience is with 40+ year old American cars.

Interesting to see that some of the Japanese manufacturers have moved to a lighter weight fluid- there are some real advantages in terms of lower friction and better fuel economy with a lighter oil, so long as it is changed out at proper intervals.

See? Even an old putz can learn a few things…

Change the fluid. Even gear lube doesn’t last forever. I’d change every 60K if no change interval is listed in the book. I, too, ignored the gear lube in my first stick-shift until 150K miles. We drained it to replace the clutch. We refilled with fresh gear lube and the shift action was very noticeably smoother. I changed it every 60K after that, and had that truck for 325,000 miles without any transmission problems.

Most manual boxes have a drain plug on the bottom and a fill plug on the side. But, I’ve seen some that fill from above, and even one that filled from the speedo cable hole (1990 Mazda Protege). The owner’s manual should have the proper method for checking the fluid level and topping off.