brake fluid or engine oil in hydraulics?

Bosun Higgs

Bosun Higgs

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My autohelm unit is a 12v motor driven hydraulic ram ( Simrad) which is part filled with a brown oil of indeterminate origin. I need to top it up and for a variety of reasons I'm not able to simply go out and buy the recommended Shell Tellus 27. The required viscosity is 15-40cST at 40 deg which is eqivalent to SAE 20 engine oil. Can be either mineral or synthetic.

I have available brake fluid, engine oil at SAE10, some pink hydraulic fluid for Allsion earthmoving kit ( Verkol Vesta c-10w), and some other indeterminate hydraulic fluid which is clear.

Question is, which to use? My inclination is the engine oil since it feels, smells and looks almost identical to the existing fluid.

What do you reckon? What exactly is the difference between hydraulic fluid and engine oil? Will it matter is what is a pretty low grade application. And how about using ATF?

The plan is to clean it all out and renew the seals anyway in August.
 
Last edited:
Bosun Higgs said:
My autohelm unit is a 12v motor driven hydraulic ram ( Simrad) which is part filled with a brown oil of indeterminate origin. I need to top it up and for a variety of reasons I'm not able to simply go out and buy the recommended Shell Tellus 27. The required viscosity is 15-40cST at 40 deg which is eqivalent to SAE 20 engine oil. Can be either mineral or synthetic.

I have available brake fluid, engine oil at SAE10, some pink hydraulic fluid for Allsion earthmoving kit ( Verkol Vesta c-10w), and some other indeterminate hydraulic fluid which is clear.

Question is, which to use?
Click to expand...

If it's designed for mineral oil, don't even think about using glycol brake fluid in it. We Citroen DS owners are very careful about this! Can you lay your hands on some LHM - Citroen hydraulic fluid? Spec is 18cSt @ 40C, so just within your spec. Alternatively, Dexron transmission fluid is about twice that viscosity.

You might find this useful - it's an exhaustive discussion of what you can use instead of LHM, so has a lot about the benefits and drawbacks of different substitutions.
 
You say you can't go out an buy the right stuff. Have you tried the internet and ebay? you'd be surprised what odd stuff you can get, pay for by credit card and get delivered to your door.
 
Hydraulic oil

DO NOT use engine oil in a hydraulic system . Engine oil contains detergents ( Bubbly ) and additives that can ruin your oil seals . Check the Transmission / power steering oils in Halfords or your local motor factors .
 
Find a hydraulic engineers near you in the yellow pages/on google and phone them or even turn up unannounced (with a suitable clean container) and chat up someone in overalls; you'll probably get some gratis or a spot of cash. Tellus27 is just a vanilla hydraulic oil, the modern spec is ISO32.
 
Just guessing, but engine oil seals are just that. They prevent oil passing the seal.
Hydraulic oil seals are used to create the barrier to high pressure fluids and work to much higher parameters. The pressure they work at would blow your average crankshaft oil seal away.
 
steering racks are very similar to autopilot rams. I would use power steering fluid. You can get some which condition the seals and could maybe save you the next overhaul .
 
Lakesailor said:
Just guessing, but engine oil seals are just that. They prevent oil passing the seal.
Hydraulic oil seals are used to create the barrier to high pressure fluids and work to much higher parameters. The pressure they work at would blow your average crankshaft oil seal away.
Click to expand...

In an emergency it's fine to use engine oil in a Citroen, but it has to be flushed out as soon as possible afterwards. Mind you, I think that's more because the suspension damping depends critically on the oil than because it does much harm.
 
ytd said:
steering racks are very similar to autopilot rams. I would use power steering fluid. You can get some which condition the seals and could maybe save you the next overhaul .
Click to expand...

And just to muddy the waters a bit more, I owned for some years an Austin Princess 1800 in which the power steering used engine oil. That must have had hydraulic rams. I also have an old sports car which uses engine oil in the gearbox. Further, tractor gearboxes use the same oil as their three point linkage hydraulics - it's variously called tractor fluid, tractor hydraulic fluid, torque fluid, universal fluid, T.D.H. oil etc. Seems that the rules aren't that simple or else it isn't as critical as some think.
 
IIRC, you should remove all the existing oil first - I thought I read not to mix different oils in hydraulic systems?
 
Your SAE 10 engine oil should be ok. Change the lot together with any filter unless that's a simple gauze which can be cleaned. Debris gradually builds up and is the enemy of hydraulic systems.

Hydraulic oil typically has an anti-foaming additive and is otherwise a fairly plain mineral oil.
 
paulm299 said:
DO NOT use engine oil in a hydraulic system . Engine oil contains detergents ( Bubbly ) and additives that can ruin your oil seals . Check the Transmission / power steering oils in Halfords or your local motor factors .
Click to expand...

'PRODUCT DATA SHEET
DESCRIPTION 10 W/30 or 20W/30 detergent/dispersant oil for agricultural tractors.
APPLICATION Naturally aspirated diesel engines not requiring Series 3 or MIL-L-2104C oils
Four stroke petrol engines of the older design, some tractor transmissions and hydraulic systems
Not for Axles incorporating oil immersed brakes.
ADVANTAGES Cost effective lubricant for non wet brake tractors.
CLASSIFICATION API CC/SD Military MIL-L-2104B
.
QUALITIES High viscosity index.
Low pour point.
Good detergent/dispersant properties for sludge and deposit control.
TYPICAL CHARACTERISTICS.
SAE 10W//30 20W30
Kinematic Viscosity @ 40ºC,mm²/s 80.0 80.0
Kinematic Viscosity @ 100ºC,mm²/s 10.0 10.0
Viscosity index 104 104
Pour Point ºC -30 -18
TBN(MgKOH/g) 5 5
APRIL 2003'

From the Rye Oils http://www.rye-oil.ltd.uk/agriculturaloils.php website. Tractor Oil Universal.

If your previously used unidentified oil had no detergent properties, accumulated sludge brought into suspension by a detergent oil could cause initial problems requiring an oil change. Water can accumulate in hydraulic systems as air flows in and out of the reservoir. An oil change tackles that problem also.
 
reeac said:
And just to muddy the waters a bit more, I owned for some years an Austin Princess 1800 in which the power steering used engine oil. That must have had hydraulic rams. I also have an old sports car which uses engine oil in the gearbox. Further, tractor gearboxes use the same oil as their three point linkage hydraulics - it's variously called tractor fluid, tractor hydraulic fluid, torque fluid, universal fluid, T.D.H. oil etc. Seems that the rules aren't that simple or else it isn't as critical as some think.
Click to expand...

It all depends on what the system is designed to use.

If it wants Tellus 27 then put Tellus 27 in. As has been mentioned before, that's pretty common stuff and I believe it isn't massively expensive either - well it wasn't the last time I used it but that was a few years ago.
If you're going to rebuild it in the future anyway then its worth you getting a can isn't it?
 
Bosun Higgs said:
My autohelm unit is a 12v motor driven hydraulic ram ( Simrad) which is part filled with a brown oil of indeterminate origin. I need to top it up and for a variety of reasons I'm not able to simply go out and buy the recommended Shell Tellus 27. The required viscosity is 15-40cST at 40 deg which is eqivalent to SAE 20 engine oil. Can be either mineral or synthetic.

I have available brake fluid, engine oil at SAE10, some pink hydraulic fluid for Allsion earthmoving kit ( Verkol Vesta c-10w), and some other indeterminate hydraulic fluid which is clear.

Question is, which to use? My inclination is the engine oil since it feels, smells and looks almost identical to the existing fluid.

What do you reckon? What exactly is the difference between hydraulic fluid and engine oil? Will it matter is what is a pretty low grade application. And how about using ATF?

The plan is to clean it all out and renew the seals anyway in August.
Click to expand...
If in doubt use tractor hydraulic oil - it's safe and (not being marine) reasonably priced.
Beg some from your friendly local farmer, he's probably got a 25litre can in the tractor shed.
Last time I needed some was in Marans, it cost me FF10 for a 5 litre can and the agricultural engineer supplied the can.
 
I'm puzzled that this has suddenly re-surfaced after 6 months but thanks for the belated advice anyway. I can't remember what I eventually put in the ram but it works OK.
 
It's now time for your annual oil change.

The Verkol Vesta will be fine, as its designed for the job. Perhaps you would like to keep a maintenance log detailing what you do to remind yourself instead of leaving it to the vagaries of the forum.:D
 
Correct oils

Just as an aside, no-one seems to be saying "what does Simrad recomend for this". Surely it would be best to ask the manufacturer of the device. Most cars etc. have warnings not to use the wrong fluid for whatever you are trying to top up, power steering fluid for steering, automatic transmission fluid for auto gearboxes, engine oils for diesel or petrol, brake fluid for brakes, hi-pressure oil for final drives, the list goes on and on, and each item can have different specs dependant on car manufacturer. The Citroen cars quoted have two types dependant on year and model, you cannot mix the two.
 
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