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Foaming Gearbox Oil


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i'm struggling a bit here and hope that someone can put me on the right track.

I've rebuilt my gearbox and overdrive and have been running it on a rig on the bench.

I filled it with Penrite 40 and ran it for about 20 minutes. all seemed well at first but the overdrive pressure became slow to recover and a bit erratic. I drained the oil and found that it had foamed into a creamy mess. The oil had recovered its normal appearance by morning so I refilled the box and ran it for 5 minutes. when the oil was drained it had foamed up again.

I replaced the oil with some Halfords Classic 20/50 and ran it again. The 20/50 foamed a bit but not as badly. I refilled the box with 20/50 and ran it and the oil looked good when it was drained.

John (Chilliman) let me have some of the EP 90 that he has used for some years so i filled the box with that and ran it for 30 minutes hoping that if all was well I could get the box back in the car but draining the box again revealed the creamy tray of foamy oil in the picture.

 

Does anyone have any ideas or comments?

 

post-2177-0-88730400-1518522865_thumb.jpg

 

 

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The creamy oil is probably a fine dispersion of air (very small size) in the oil. Not water, as that would not clear so much and you have replaced the oil several times so there should not be any water.

Like you I also do not understand where the dispersion takes place. Can there get air in the suction to the pump?

Is the filtergauze clear?

Good luck,

Waldi

Edited by Waldi
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Hi Andrew,

was the Penrite 40 a gearbox oil (as per GB40) or a 40 grade engine oil?

The Halfords 20/50 is an engine oil.

 

It is possible that the above (engine oils) have detergents in them to keep the oil ways clean - if so they may well foam due to the gear teeth interaction.

 

The EP90 shouldn't foam - but could old age lay a part !!!.

 

or possibly a fault with the OD HP side of the pump etc

 

Roger

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The foaming is certainly micro bubble aeration.

The Penrite is GB40 and seems to be a little more viscous than the EP90.

The 20/50 is much less viscous and the gearbox is more noisy with this oil which was run as an experiment as I had some spare. I would have expected this to foam more than the gear oils and dont want to run on an engine oil long term.

I was wondering if the oil is aerating as it gets forced through the small orifices and leak paths in the high pressure overdrive control system but the pump is a very low flow rate and the oil seems to foam very quickly on the gearbox side and possibly less so in the overdrive side.

I'm still experimenting but not getting anywhere yet.

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Can I suggest you make use of the telephone as you are getting into an area where there appears to be little expertise here and we are all guessing a bit but all want to find the solution.

 

Both Castrol, Morris Oils, Penrite and Millers Oils make specific Classic Oils and they have technical support departments that are very friendly and are staffed by people who live and breath oils.

 

Give them all a phone call and get the answers from the experts.

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Ive spoken with Pete Cox, ORS, and have emailed Penrite technical bods without any real success although Pete did say that he had noticed aeration before when bench running.

I thought about the fact that the thinner 20/50 seemed to fare better and looked at running temperatures. Bench testing until the temperatures stabilised took about an hour and saw temperatures of 25 to 30 degrees; much lower than what can be expected in service.

I ran the unit from cold with a paint stripping gun aimed at the gearbox sump and didnt notice any of the fluctuating overdrive pressure previously observed after extended running. After running for half an hour the temperature had reached 35+degrees and everything seemed in order. I drained the oil and found minor aeration with zero foaming????

I expect that in service the box will run hotter and aeration will be further reduced when the oil viscosity is reduced.

Had I refitted the gearbox without bench testing the perceived problem would never have surfaced but on the plus side I wouldnt have learned anything about gearbox lubrication and Ive got some material for the Devon Group In the Garage newsletter.

Hopefully all will be well when the unit is road tested.

 

Perhaps all those years as an aerospace development test engineer have left me tending to look at things a bit too closely. ????????????

 

Thanks for the interest and comments.

Edited by Drewmotty
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Hi Ian,

...but the consensus of who!!!

Every engine/GB/OD builder has his/her own take on things.

 

Engine oil has no EP properties so the OD may be unhappy

But then the OD is a simple gearbox so shouldn't require EP. But at least consider a gearbox oil.

 

The OD had an original oil spec that specifically ruled out EP oil (in the 50's_ but then TRiumph changed it to EP in the 60's but why?

 

When a GB builder specifies 20/50 is he talking about engine oil or a multigrade suitable for GB's

 

I'm a simple chap I put engine oil in the engine. Gearbox oil in the gearbox and diff oil in the diff

 

But then anything slippery would almost certainly work.

 

Roger

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I can tell you that amount of foaming is not good and can cause micro pitting and cavitation, leading to pump failure,

 

All Gear oils should have an indicated air release time which is expressed in mins , so you can check if the product meets that spec..

Moving to a multigrade 20/50 will give you a lower viscosity than an EP 90 and a different EP additive, Zinc instead of Sulphur Phosphorous . The lighter product should release air quicker . A simple way to test is to place a quality of oil in a clean bottle at a known temp , shake and then time the oil till it clears. and repeat with each oil . I would add that air entrainment can be increased by solvent contamination , water contamination, pump drawing air and reduced anti-foam additive. Silicone anti-foam additives deplete over time ... one of the many reason you should change the oil.The addatives in gear oils are more suited to shock loading than engine oils, so would stick with a gear oil .. The viscosity improvers in multigrade engine oils shear down in gear boxes, effectively reducing the viscosity.

 

Re engine oils in gearboxes . There were some concerns, at the time that some of the active Sulphur Phos additives caused pitting in Phos bronze and the friction modifiers cause O/D clutch slip. I would that the chemistry of the additives has changed considerably and that O/D clutch material has also improved, so these should be less of a problem.

I use a 75w/90 in my 3A but I have rebuilt the gear box and O/D . Filling was done with the top cover off and all seals were replaced with Viton seal and I have no issue in 8 years .

cheers

NOBBY

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The important lesson here is that, regardless of the grade, gearbox oil will aerate and foam when cold causing cavitation of the overdrive pump and reduced lubrication properties. So take it easy until things are warmed up properly as you are likely to cause excessive wear in the gearbox as well as the engine.

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I had a similar situation on a 1948 Vauxhall gear box.

Recently acquired, I took the car for a run to warm up the various

lubricants.Draining the gearbox resulted in a quantity of foam the

consistency of Angel Delight (if you can remember that!).

Somewhat concerned I refilled with the correct 90 grade, took it for

another run, drained the oil, and ended up with the same foam.

I refilled again with more of the same.

I decided, in the absence of any other authority, that that was how

it should be!

Done 2000 miles since with no probs!

 

Roger M-E

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If you are using a gear oil it has VERY low levels of dispersant and detergency but does have antifoam additives,, Detergents and dispersants are present in engine oils to clean insolubles from the internals and to hold them in suspension. (and are not relevant for gear oils) so that they collected in the filter or are removed when the engine oil is drained . Gear oil additive packs contain , anti-wear additives, extreme pressure additives, anti-foam and anti oxidants.

The anti-wear additives and Extreme Pressure additives are different and some EP additives don't start working till friction builds to 140C+ during shock loading

There are many additives in engine oils that are not present in gear oils and most are redundant in gearbox applications.

 

.There are a number tests that can be used to demonstrate the gear oil performance but most are not carried out on automotive oils, if its possible to get an FZG rating for the engine oil and 11> or <12 is good marker / Most Militaries have engine oils that can be used in gearbox applications but they tend to be monogrades as apposed to mutigrades. As I mentioned before the VI improvers used in multigrade engine oils sheer down in gearboxes, however multigrade gear oils 80w/90, 85w/140, 75w/90 do hold their viscosities well .. I would also mention that base oils are as important as the additive pack, so buying a cheaper oil can be a poor choice. longer term...The Castrol Classic range are good as are the Shell automotive range, E.M and Gulf oils.. I can provide more info if anyone is interested or is as sad :)

I would check O/D pump pressure and purchase a major branded 80w/90 API GL4 or 5 gear oil. The gear box temp operates hot, due to proximity of the exhaust. I run shell spirax 75w/90 which uses sheer stable base oils and have had no problems

but please be aware that even if your mileage is low a 2- 3 year oil will suffer additive depletion.

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