Tech Tips:
Gearbox Oil (1)

Background :   One list member claimed that the "correct" type of oil to use in a Hillman "Series" Minx gearbox is 30W non-detergent engine oil.
A few people expressed surprise, stating that they had been using 80W gear oil.  However, this is definitely incorrect oil for Series Minxes etc.  Rootes clearly specified in the Owners Manuals that engine oil is correct.
Some really oldtimers (e.g. 1930s Hillmans) do require gear oil in the gearbox.  Always consult your Owners Manual.  If you don't have one, ask someone who does.  This is important.

Back to the original statement about "30W non-detergent engine oil"
Some of us then wondered whether the "non-detergent" aspect is important.  Could we use a normal detergent-type engine oil instead ?

From: Victor Hughes [hughes(at)scides.canberra.edu.au]
Sent: Friday, December 06, 2002 12:34 PM
To: Hillman list
Subject: "Hillman - " Tranny Oils

This message forwarded by the Hillman List.

Following up the thread that was running a couple of days back about detergent Vs non-detergent oils I did some research including contacting tech departments at Shell, Castrol and BP.

First, the term 'detergent' does not mean the oil has washing-up liquid added.  It refers to a property of the oil, namely an ability to keep insoluble particles (like sludge) in suspension (rather than deposited somewhere).  Certain additives are used to give oil this property, but they're not what we think of as 'detergents'.

Next, foaming or frothing is a potential problem with both detergent and non-detergent oils, so both have 'anti-foam' agents added.  To quote BP  " the defoam is there to prevent oxygen build up which occurs from circulation ........ it is not present to reduce the effects of detergency.  Too much oxygen in any lubricating system will reduce the lubricating effects of the oil causing premature wear."

So it seems that potential foaming is not the reason for not using detergent oil in trannys.  What then is?  Well, Shell ignored the question.  Castrol thought it might be  "because back in the '60s it was considered best not to emulsify any water that got into the transmission".  BP said  "There are several reasons why non-detergent oils are recommended, the main reason is that non-detergent oils are also very low in other additives such as zinc and calcium.  Zinc and calcium can cause premature wear of certain components which may have been used in the gearbox."

If you want to learn more about oils, this site has a dictionary of oil terms.


The 3 oil companies I contacted (from links at their websites) all responded within 24 hours (Castrol within 30 minutes).  There recomendations for these transmissions were:

BP -   Vanellus C Mono 30 or Power Multigrade MO or Visco 2000
Castrol -   CRB 30
Shell -   Lawn 4


From: Jan Eyerman [jan.eyerman(at)usa.net]
Sent: Saturday, 7 December 2002 9:00 AM
To: Victor Hughes; Hillman list
Subject: "Hillman - " Oil

This message forwarded by the Hillman List.

I think they answered your question.... detergent oils pickup and carry all the bad stuff with them, depending on an oil filter to filter it out.  This is OK in an engine that has an oil filter, but not so good in a transmission that doesn't.  In that case you would prefer an oil to leave the bad stuff where it is and not carry it around to other spots in the trans.

However, I think it really is a moot point.  There are few nasty things getting into a transmission-unlike an engine where various stuff filters past the rings and pollutes the oil.


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