Transmission fluid change

Tiny
ELOPEZ07
  • MEMBER
  • 2001 NISSAN FRONTIER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 125,600 MILES
Two years ago my inherited this vehicle with about 108,000 miles on it. Since then we have used the truck off and on since it serves as an additional recreational truck. The truck currently has about 126,000 miles. I have been wanting to change the transmission fluid to keep up with the basic maintenance since I am not sure when the last time it was changed.

I was told by friends and my trusted mechanic not to change the transmission oil since I have no history as to when it was last changed because the transmission will fail.

If I do change it, it is true that I run the risk of the transmission failing? This does not make sense to me, as I am simply changing old fluid with the new to preserve the integrity of the truck. Any thoughts or recommendations in how to proceed?
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Monday, June 19th, 2017 AT 12:16 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
If someone tells you changing the fluid will cause damage, ask them to explain their reasoning. They may be thinking of a transmission flush service. There are mixed opinions on that. Changing the fluid and filter simply restores the worn-out additives and removes much of the varnish that has formed from the fluid being hot. Only about half of the old fluid drains out and needs to be replaced. The flush gets pretty aggressive and replaces one hundred percent of the fluid. A strong detergent is added first, then must be removed as part of the flush. Some of us feel that detergent can dissolve some of the friction material on the fiber clutch plates.

My limited experience from talking with people who have had flushes done is they were usually trying to solve a pre-existing problem, and when the flush did not solve it, and that problem became worse, they blamed the flush for the transmission's failure. In fact, the failure was likely going to happen anyway. My opinion is if there is no problem now, there is no value in having a flush service performed, and if there is a problem, a flush is not likely to solve it. If there is any slippage problem, that is due to wear of the clutch plates or a cracked or torn rubber lip seal in the clutch pack. Those are mechanical problems and a flush will never fix a mechanical problem. If the fluid and filter change is way overdue, varnish build-up in the valve body can prevent some of the shift valves from sliding smoothly and freely. That can result in delayed or late shifts. A flush, with that harsh detergent, may solve that, but given some time, the severity of that problem is likely to be reduced just from the new additives from a fluid and filter change.
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Monday, June 19th, 2017 AT 10:37 PM
Tiny
MBA2004
  • MEMBER
Hello. I would like to clarify on what I want to do and hopefully you can provide a simple yes/no based on your experience. All I want to do is drop the pan and change the filter not do a flush. I have no existing issues and the truck is solid. Just want to make sure it last for a long time. I am staying away from the flush option simply because of the horror stories about doing a fluid on high mileage vehicles.
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Thursday, May 3rd, 2018 AT 9:57 AM
Tiny
CARADIODOC
  • EXPERT
For decades all we had was the fluid and filter change option. The flushing machines came about when transmissions were down-sized for cost-cutting and problems became more common. When you are not having problems, a fluid and filter change will replace about half of the fluid, and that will get you plenty of new additives such as seal conditioners and detergents.

My experience with this is limited, but I can share that the greatest benefit to flushing the system is to clean out the transmission cooler. In fact, doing that is required to put the warranty in force for many replacement transmissions. There are special pumps made for that purpose that do not flush the entire transmission, just the cooler.

If someone tells you the goal of flushing the transmission is to get the grit and metal chips out, be aware if those are in the clutch packs, they have already chewed up the rubber lip seals and you have major problems. If a metal chip or speck of dirt makes its way into the valve body, a valve can stick and you will have shifting problems where it stays in one gear at the wrong times.

The other concern is varnish build-up in the valve body. That can cause a valve to stick, but that only applies to which gear the transmission goes into or stays in. Sticking valves do not cause slipping. We do not hear of varnish problems often because changing the transmission fluid periodically removes most of it, and the additives do the rest. A flush is usually preceded by adding a can of highly-concentrated detergent to dissolve that varnish. I think I would be more worried about what else that detergent is acting on than any varnish left behind.
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Thursday, May 3rd, 2018 AT 2:11 PM

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