Changing fluids

  • 5.3L
  • V8
  • 4WD
  • 163,000 MILES
I just bought the truck listed above. What fluids should I change and should I do a transmission flush or just change the oil and filter?
Do you
have the same problem?
Thursday, April 6th, 2017 AT 6:12 PM

1 Reply

The jury is out on the value of flushing a transmission. Too often people hope a flush will solve a problem that already exists. When the problem becomes worse, the flush gets the blame. If the problem is caused by a mechanical failure or excessive clutch plate wear, no flush is going to magically fix that.

Standard procedure used to be to drain the transmission fluid and replace the filter, typically around every 36,000 miles. That removed only about half of the old fluid, but that was enough to replenish the additives. Today the bean counters have given us transmissions that just barely hold up to normal use, and maintenance services have become more important. Operating temperatures can be higher too, and that leads to the formation of varnish. When that builds up on bores in the valve body, a valve can stick and cause a failure to shift properly. With older hydraulically-controlled transmissions, that could just mean you needed to reach a speed a few miles per hour faster before a pressure would increase enough to force a sticking valve to move. You often never noticed that. Most transmissions today are electronically-controlled. Some fluid pressures remain constant and are not influenced by road speed. If a valve sticks at any speed, it will not "unstick" at a faster speed. This is where a shifting problem might be solved with a flush, but only if that flush includes introducing a highly-concentrated detergent first to dissolve the varnish.

In general, a lot of people feel if there is no problem with the transmission, there is no benefit to the flush, and if there is already a problem, a flush is unlikely to solve it. The stories we hear about are when there was no problem, but something happened shortly after a flush. The problem is we never get to hear the history leading up to the problem, and we do not usually get to learn the repair that solved the problem. For example, if during a rebuild, it was found that rubber lip seals were hardened from age, and had cracked apart, that was a mechanical problem that a flush was never going to solve, but the service could have caused the seals to break apart even more, resulting a major problem. The problem was going to show up anyway. The flush just made it happen sooner, but it got the undeserved blame.

I would opt for a fluid and filter change, and a standard oil change. After that, you will have the best luck if you stick with the same brand of engine oil. If you switch brands at every oil change, you can run into an additive in one that is not compatible with an additive in the old oil. Examples of that are a seal conditioner that is dissolved by the new detergent, or a dispersant that will not dissolve and carry to the filter an anti-foaming agent that has accumulated in the bottom of the oil pan.

Unless specified differently by the manufacturer, we do not change power steering fluid or axle gear lube. If gear lube needs to be replaced after a repair service, a whale oil additive must be added for most locking, or limited slip, rear axles. That prevents them from chattering when cornering. You will not find those in front axles on four-wheel-drive trucks.

All manufacturers recommend periodic brake fluid replacement to get the moisture out that accumulates in it, but few of us actually do that. The moisture causes corrosion of metal parts, and it lowers the boiling point of the fluid from well over 400 degrees to 212 degrees. That can lead to one form of brake fade that includes a mushy brake pedal.
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Thursday, April 6th, 2017 AT 7:08 PM

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