We have an '89 31 ft gas Ford 460 and were pulling up a 4 mile 8-10% grade and the trans oil temp got up to about 170 and the engine oil up to about 180. this seems high, what would normally be expected?

Both are quite cool. IMHO, max intermittent for the transmission is 250F, engine oil about the same. Neither will suffer any breakdown at the temps you've experienced.

I had this posted a little while ago and just found it.

Rusty is spot on, don't sweat it. This is why rocking out of mud and snow will burn out your transmission.

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The approximate life expectancy at various temperatures is as follows:

. 175°F - 100,000 miles optimum street temps
. 195°F - 50,000 miles max street temps
. 212°F - 25,000 miles fluid fatigue
. 235°F - 12,000 miles varnish forms
. 255°F - 6,250 miles seals start to harden
. 275°F - 3,000 miles
. 295°F - 1,500 miles plates start to slip
. 315°F - 750 miles seals and clutches burn out. Oil forms carbon
. 335°F - 325 miles
. 355°F - 160 miles
. 375°F - 80 miles
. 390°F - 40 miles
. 415°F - Less than 30 minutes
. Above 295°F, the metals inside the transmission will warp and distort. This is why rocking in snow, mud, sand etc. should not exceed a few minutes.

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Bill N.Y.

Many sources say 285 deg is the maximum sump temp for short duration, such as hill climbing.

quote:

The approximate life expectancy at various temperatures is as follows:

I've seen that chart many times. Question is, since it's been around a while, does it apply to synthetic ATF?

Mike

quote:

Originally posted by Relative:
I've seen that chart many times...does it apply to synthetic ATF?

Great question. I really don't know. I'll tell you some things I have observed and some things that are universal.

I bought a brand new Freightliner FL70, Cat 3126 with an Allison transmission several years ago. After owning it for two months I found that the truck I ordered did not come with everything I paid for. One such item was the synthetic transmission fluid I paid for.

The dealership took it back, flushed and refilled it with the proper stuff. The three months I did have it before this the transmission ran hotter then after the synthetic was added. Why is this important?

If you ran synthetic and can lower your operating temps then your components will last longer. I know this isn't an Earth shattering revelation, your question about synthetics lead me to believe your asking the baseline question "is all things equal?" That answer is more complicated...

Your seals will harden and start to wear out, the plates will slip, the clutches will burn up, metals will warp and distort if the temps reach certain stages. The synthetic fluid, being of a different type, will have different characteristics and will react in stages different then the chart. How much, I don't know.

With synthetics you should be able to prolong the life of the transmission if you stay within the proper ranges. The statement: Many sources say 285 deg is the maximum sump temp for short duration, such as hill climbing. I've heard this before too and while it may be correct (I don't know) I still cringe. I have never gotten anything I've owned that hot! I would tend to agree more with Rusty's statement: max intermittent for the transmission is 250F. If in doubt, I would go lower!

What is considered "short term"? 1 minute? 2 minutes? 30 seconds? Is it longer then my wife telling me "just a second" or "another minute"? The wording "short duration" is a subjective one.

You would need to figure out the cumulative affect of many times of raising the temp and duration of said act. By looking at the chart and knowing that 15 degrees one way or another really does different things inside of the transmission should help most people realize that there actions do have consequences. Other people, you could talk or type until your hands fall off. I'm Italian, so I talk with my hands. See, look at how long this post is already.

Synthetics for the transmission are a good thing. Lowering temps will allow for longevity in your equipment if things are kept cooler. The act of overheating should take longer to achieve. I just don't know if varnish, fluid fatigue or carbon still fall within the ranges on that chart.

A good gauge will help you figure out what temps your running and if maybe you should stop trying to rock out of the snow/mud or if you should pull over and let your coach idle until things cool down a little.

The answer to the synthetics makeup and longevity at varying temperature should come from Rusty. Rusty's experience comes from being a marine engineer, a fuels and lube engineer for a major oil company, and one of the Navy's "Fuels and Lubricants Technical Officers".

That 285 degree figure came from my GM manual. I wonder how long a hill they mean. Bishop to Mammoth is a long hard pull.

quote:

Originally posted by bill h:
That 285 degree figure came from my GM manual.

Seeing that above 295°F, the metals inside the transmission will warp and distort I can see why they would say that.

Looking at one line from the chart.
235°F current operating temperatures
12,000 miles This is how long your transmission would typically last if you kept doing it. That's basing this on a new or low mileage transmission and all things being equal. What do you think is happening to a transmission with 137,000 miles already on the clock?
Varnish forms inside the transmission. This is what's happening inside of the transmission within a few miles. The longer your doing this the worst it's going to be. The 12,000 miles doesn't mean that it will take that long before varnishing starts to take affect.

Seeing that at these temps;

212°F the fluid is starting to fatigue

235°F varnish is starting to form

255°F seals are starting to harden
I (meaning just me) would be hard pressed to exceed the 235°F for even 30 seconds. Your not going to get the varnish out of the galleys, psi check valves, springs, plates etc... Now if Rusty tells me that varnish starts to form at a higher temp with synthetics then I would exceed 235°F but never go above the 255°F mark. Why would I want to make my seals leak? Now were closer to Rusty's statement of 250°F.

Bill N.Y.

Intermittent - not meaning 10 minutes at load, 10 minutes off, but at the occasional long grade pulls where the temp creeps up, followed by normal cruising, 250F isn't going to hurt the ATF or the engine oil. Both can cope well with occasional abuse.

The effect of temp on ATF is to accelerate breakdown (mostly oxidation of the base stock and impurities). That won't be measureable in 10 minutes at 250F, and the issue is far less with synthetic ATF, since the base stock is homogeneous, and there are far fewer impurities.

Engine oil gets changed frequently, and it has additives to deal with nasty stuff, where ATF isn't and doesn't.

For normal cruising, IMHO max sustained would be 210F for the tranny and 230F for the engine oil. Naturally, lower would be better, and the temps Dave S reports are about right - too cold can be a problem also.

Anyway, varnish (simple answer) is caused mainly by oxidation, or mechanical breakdown, of the base stock or imbedded impurities. Synthetics minimize (but don't totally eliminate) most of both problems. The bulk of the issues, such as varnish, arise from prolonged service, whether at high temps or normal, but higher temps accelerate the process. So the bottom line is that if one finds tranny temps frequently exceeding 250F, the fluid should be changed more often.

As Bill N Y points out, references to "short-term" and other descriptions are, IMHO, "weasel words" from the manufacturers to do the shuck and jive in the event of a customer complaint. (My fave is the GM claim that 600 miles-per-quart is "normal" oil consumption for the 5.7L and 7.4L gaso engines).

Anyway, more to the point is that the cooling for the tranny should be designed to keep temps at or below 210F (lower is better) except in extreme conditions (climbing a long, steep hill in 105F temps). A tranny at 285F would be cause to check out and/or augment the cooling system for it.

As I've mentioned before ad nauseum, "Oil is cheaper than metal".