Jump to content

Correct Oil?

Recommended Posts

I want to top up the power steering reservoir on my Militant Mk 3.

The handbook says the correct oil is OM13, and I see from various threads on here (e.g. http://hmvf.co.uk/forumvb/showthread.php?9292-What-do-you-use-instead-of-OM13) that the Morris equivalent is alleged to be Liquimatic No 1 (ISO 10 viscosity) although there seems to be a difference of opinion on the exact viscosity.

At some time in the past the steering system seems to have been replenished using possibly ATF, as it has a red colouring and so I do not want to put a different fluid in there if it may be incompatible with the ATF.

The steering makes a noise under load when starting from cold but which goes away when warmed up, which has prompted me to check the fluid level; it needs topping up, but the reservoir is not empty.

I have phoned Morris's technical line, quoting the original spec of OM13, and the initial answer was that I would need to find out what OM 13 was before they could tell me their equivalent, however when I explained that was why I was phoning them, he then said I would need at least Liquimatic No 2 (ISO 15 viscosity). I mentioned the correspondence on here and that Liquimatic 1 seemed to be an equivalent, but he was adamant that No 2 was required. Their price is circa £85 plus VAT for a 25 litre drum.

I have also phoned Miller's oils who have a depot in Glasgow, telling them that I need a 10 viscosity hydraulic oil, and they recommended their Millmax 10 (£60 plus VAT for 25 litres). Although their technical help sounded less professional that Morris's, he said that ATF is considerably more viscous than 10 and that the noise I am hearing is probably caused by the oil being too thick when cold.

Millers were happy that there would be no chemical incompatibiity between their Millmax and the ATF, but Morris's wouldn't give any advice about compatibility issues without knowing for sure that the existing fluid is actually ATF. Obviously I would try to drain as much as I could of the existing fluid before refilling with new stuff, but it will be impossible to ensure absolute chemical cleanliness without major dismantling.

So the questions:

What is the correct ISO viscosity rating for OM13?

What does anyone else use for a similar application?

Can I stop worrying about incompatibilities between oils- I am thinking about seals etc?

Has anyone had any quality issues with, or have any opinions on either Millers or Morris's?

Edited by Iain Crosbie
Link to comment
Share on other sites

Hi Iain.


In a word - OM13 is a hydraulic oil and as such, there is very little difference between the varoius types of hydraulic oil.


I would imagine you will have no problems putting any hydraulic oils in the system between ISO10 - ISO15.


It's pretty much all the same thing.


Others will disagree but I do tend to think a lot of head scratching occurs when people start talking about the correct oil types.


Sometimes it does mattter when referring to different types and grades of oil, bronze components etc, but with a Milly steering pump, a hydraulic oil is a hydraulic oil.


I used ISO15 in my Mk3 recovery and as yet - the steering wheel has not fallen off. lol


Not sure about using ATF though?



Link to comment
Share on other sites

Hi Iain, the ISO viscosity is 13 for OM13, Currently there is only ISO 10 or 15 available. I have been using ISO 15 for the last 20 years or so in my Saladin and other vehicles with no issues. The difference in viscosity is very slight, and makes no difference, I went for the slightly higher grade , but in reality its not so sensitive. OM13 was originally speced as a normal mineral hydraulic oil with stearic acid added. I remember talking to a technical adviser at Silkolene backin the 1980's, as they then had the MOD contract for OM13, and he said that it was used as to improve its lubrication properties for some projects that used a long hydraulic ram. He suggested Derwent 15, an ISO 15 grade oil. I've used several other makes over the years as well with no issues.

Link to comment
Share on other sites

  • 3 weeks later...

Im a hydraulics engineer and can confirm the ISO 10w and 15w comment made.

Sod all difference in them and the OM is equivelant to an ISO 13.

We use mainly ISO 46 and ISO 32 all day long, the 32 goes in the older machines with a bit more wear in them!

Dont worry about mixing ATF oil, it mixes with all Hydraulic oil grades.

Just because its red doesnt mean its ATF either, JCB put a red dye in their ISO 46 and tell you that you need their "special" oil only and charge you the earth for it!!! LOL

I have also seen it in GREEN and BLUE!!!!

At the factory they only put ATF in the hydraulics of most Cherry Pickers because of the lower viscocity. Only because they dont know the climate the machines are going to, could be hot or sub zero! We always top the tanks up with HYD 46 (ISO 46) as recommended by NATIONWIDE ACCESS who supply them!

Any problems let me know I have a good source for oils and lubes if required.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...