What are the Dangers of Mixing ATF & Engine Oil?

[lpdsn]

I'm still struggling to get at the drain plug for my gearbox. Still got a couple of ideas to try, but I might have to face up sucking the old gearbox oil out.

Trouble is I don't know what's in there except that it is overdue for changing. I'm assuming the worst case and it is some form of engine oil. I know not to mix ATF and engine oil. The new stuff is Dexron II as recommended by the manual.

So assuming it is engine oil in there at present and that sucking doesn't get the last dregs out, what are the risks?

 

[Jcorstorphine]

Why not drain or suck out as much as you can then fill with correct amount. Run engine in fwd and rev for a min then drain/suck out the oil and then do a final fill. By doing that you will have diluted residual oil.

 

[Quandary]

It is not a Volvo is it? D1 series engine/gearbox manuals specify ATF in the gearbox but a couple of years ago Volvo decided it was fine to just use engine oil, a cynical friend suggested it was because Volvo get a good price for their engine oil in the blue bottles but did not sell an 'own brand' ATF.

 

[lpdsn]

Why not drain or suck out as much as you can then fill with correct amount. Run engine in fwd and rev for a min then drain/suck out the oil and then do a final fill. By doing that you will have diluted residual oil.

That's the plan. Just looking to see if anyone can tell me what effect the mixing will have and what proportions are problematic.

 

[VicS]

I'm still struggling to get at the drain plug for my gearbox. Still got a couple of ideas to try, but I might have to face up sucking the old gearbox oil out.

Trouble is I don't know what's in there except that it is overdue for changing. I'm assuming the worst case and it is some form of engine oil. I know not to mix ATF and engine oil. The new stuff is Dexron II as recommended by the manual.

So assuming it is engine oil in there at present and that sucking doesn't get the last dregs out, what are the risks?

When VP changed from ATF to engine oil in most of their sail drives they said it did not matter if some ATF was left in the lower gearbox. This implies that there is no problem if they are mixed

 

[lpdsn]

It is not a Volvo is it? D1 series engine/gearbox manuals specify ATF in the gearbox but a couple of years ago Volvo decided it was fine to just use engine oil, a cynical friend suggested it was because Volvo get a good price for their engine oil in the blue bottles but did not sell an 'own brand' ATF.

Yanmar. Kanzaki-Carl Hurth KBW21 Gearbox. Manual recommends changing ATF every 150 hours. What's in there is 8+ years old, so overdue.

I can get the right ATF just as cheap as engine oil.

 

[lpdsn]

When VP changed from ATF to engine oil in most of their sail drives they said it did not matter if some ATF was left in the lower gearbox. This implies that there is no problem if they are mixed

Thanks Vic.

 

[Jcorstorphine]

I got a bit concerned with what oil I had in my Hurth gearbox and what I should use. I did recall that the original oil was red and was sure that it was ATF made by ESSO and called Type A which was no longer available.
Anyway I came on here for advice about the dangers of changing from ATF to Synthetic or mineral type oil.
The explanation I was given was that one of the oils caused the shaft seals to swell slightly which was ok so long as you kept using the same oil but if you changed to a different type of oil, the the original oil which had been absorbed by the seal got leached out by the new oil causing the seal to fail.

Problem is I can't recall which oil did what but I will try and find the postings and get back.

 

[lpdsn]

Problem is I can't recall which oil did what but I will try and find the postings and get back.

Thanks. That would be interesting.

The only thing the manual actually cautions against is "When adding oil between oil changes, always use the same type of oil as in the marine gearbox." i.e. don't mix types of oil. Nothing about not changing to a different type when changing the oil, but...

 

[reeac]

My understanding was that ATF was a quite regular mineral oil but with anti-oxidant and anti-foaming additives. I own an old car which has ordinary engine oil in the gearbox and I used to own a manual transmission Jag. which used ATF ....I believe simply to permit tracking any oil leak to engine or gearbox. Of course there may well be subtleties regarding oil seals.

 

[elton]

You better make sure the ATF is the proper type for the box. There are two types and they're not interchangeable. My local dealer sold me the wrong type, and it trashed the box. I was not pleased, but had no evidence. It was the end of the car.

 

[Jcorstorphine]

Thanks. That would be interesting.

The only thing the manual actually cautions against is "When adding oil between oil changes, always use the same type of oil as in the marine gearbox." i.e. don't mix types of oil. Nothing about not changing to a different type when changing the oil, but...

Here is the link to posting on oils. It is more towards the choice of straight or synthetic oils but hope it helps. Look for posting No 10 by superheat6k

http://www.ybw.com/forums/showthrea...ide-to-oil-for-HURTH-ZF-gearboxes-and-its-ATF

 

[lpdsn]

You better make sure the ATF is the proper type for the box. There are two types and they're not interchangeable. My local dealer sold me the wrong type, and it trashed the box. I was not pleased, but had no evidence. It was the end of the car.

It's OK, I have the manual. The ATF I have is Dexron II, which is one of those recommended.

 

[lpdsn]

Here is the link to posting on oils. It is more towards the choice of straight or synthetic oils but hope it helps.

Thanks. New stuff is mineral, so only risk might be if I switch to synthetic in the future.

 

[jdc]

As ever Wikipedia is one's friend here and it states "Most ATFs contain some combination of additives that improve lubricating qualities,[2][3][4] such as anti-wear additives, rust and corrosion inhibitors, detergents, dispersants and surfactants (which protect and clean metal surfaces); kinematic viscosity and viscosity index improvers and modifiers, seal swell additives and agents (which extend the rotational speed range and temperature range of the additives' application); anti-foam additives and anti-oxidation compounds to inhibit oxidation and "boil-off"[5] (which extends the life of the additives' application); cold-flow improvers, high-temperature thickeners, gasket conditioners, pour point depressant and petroleum dye"

To the question "Are the properties of ATF adversely affected by dilution with mineral oil?" a general answer would depend on the application and on the meneral oil's own spec. But the situation is greatly simplified by your situation in that the gearbox is clearly happy with either what it already has (it's worked fine for many years) or with ATF (it's what's specified). So any mixture from 0% through 100% is probably just fine as far as performance is concerned.

Hence the only remaining question in your case seems to me to be whether mixing them could cause something other than just intermdiate properties of the two oils, for instance a reaction between additives causing some new and undesirable property. In principle I suppose it could(1), but it seems highly unlikely provided your old oil wasn't something extremely weird.

A long-winded way of saying don't worry! Just change the oil.

(1) thought experiment. Lubricant type 1 is the stuff in the red Araldite tube, lubricant type 2 is the white. Works just fine whichever one uses, but not too good if mixed! However I don't suppose for a millisecond anything like this could occur!

 

[lpdsn]

Went for it. As I feared, I didn't get a huge amount sucked out by the dipstick hole. I reckon about 60%. I'll run the boat in gear a bit tomorrow and try two more rounds which should get me down to about 6% original oil. I should have enough spare to change it again a couple of times in the spring.

Glad I went for it, the old stuff is quite brown, although luckily there's no burnt smell.