I'm sure I'll likely get the specific answer to this question once I replace them, but two long time Jag mechanics have now concurred that my slow but significant power steering fluid leak appears to be the reservoir->pump supply hose and low pressure pump->reservoir return hose.


Here's what I'm wondering.... why are these hoses leaking and not the high pressure hoses of the same vintage?

The 'supply' hose has no pressure on it whatsoever other than gravity, and is secured with spring clip clamps at both ends. I don't know yet if the leak is at these junctions or the hose is split/weeping, but....

And similarly for the return hose, while is has some pressure pumping the fluid back to the reservoir, it too is very low I'm sure. This hose as a screw-in connector with an o-ring at the pump, but again has a simple spring clip clamp at the reservoir end.

So with all that background, anyone else have any experience with these two hoses leaking and why they tend to other than just age/fatigue of the rubber of the hose itself? e.g. Is it as easy as needing tighter/better clamps?

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Unfortunately, just like me, mine dried out became hardened and quite useless.
Nevertheless $90 at the Grand Touring dealer ship made the top hose better again. Unfortunately I'm still the same

 

I had to replace the reservoir hose a couple times during the course of my ownership. I can't explain why they leak....never really investigated very much to be honest. But, yeah, you normally have more problems with the pressure hoses....

<shrug>


Cheers
DD

 

Thanks, that is interesting data. Makes one think there must be a design (material?) defect that the AT fluid is not compatible with. Maybe Jaguar mis-spec'd the material in making some assumptions that this low(no) pressure hose didn't need to be as tough as the pressure hoses?

I wonder then if this is one of those cases where an aftermarket hose, say from a hydraulic hose supply house, would be better than OEM?

Interesting....

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So, the MNA3980AC (part 18 in the diagram) reservoir to pump supply (or sometimes called suction) hose is anywhere from $30-60USD which is a bit silly as it is just a plain hose with no special connectors, etc. It does have a short molded bend at the reservoir end, but I'm not sure that is worth the high cost

Now, I actually am a proponent of OEM parts when it makes sense as I think it is likely the fit and quality of OEM has value.

But in this case I have to wonder if a standard piece of 5/8" (guessing at the size from my office chair, but likely) transmission cooler hose would be as good if not better than the OEM piece that seems to be leak prone, and of course that would cost about $5 or less.

Any thoughts on why a standard piece of transmission cooler hose from my chain auto parts store wouldn't be a good choice for this hose?


I plan to get the real OEM part MNA3990AC (part 1 in the diagram) for the return line as it has a specific fitting at the pump end.



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I see no problem with a replacement using generic hydraulic/steering/transmission hose.....if you can manage the bend.

Cheers
DD

 

Strangely enough my power steering reservoir hose also leaks. Maybe when I put a new one on I will also use a better hose clamp.

 

Al,

That low-pressure hose from the reservoir to the pump is the most common source of P/S leaks on the XJ40 also. The collective assumption in the XJ40 community is that it's the hose's proximity to the exhaust that causes it to harden and lose its ability to seal, most often at the reservoir end. I've never had a problem with any of the other hoses, which are all original on our '93 at 197K miles. But I've probably replaced that silly low-pressure hose four or five times. As you assumed, any good oil-resistant 5/8 in. I.D. hose will work just fine:

Welcome to Jag-lovers - Members Photo Viewing Page


One thing I've come to wonder, though, is whether it might be prudent to use the newer spring clamps that apply pressure equally around the entire circumference of the fitting, instead of the worm-drive hose clamps that were originally equipped (at least on our XJ40). According to Pat Goss on MotorWeek TV, worm-drive clamps should not be used on plastic fittings, such as the ones on a P/S fluid reservoir, because the fitting/nipple will tend to expand into the recess under the clamp screw. I can't detect anything like that on our reservoir's fittings, but it makes me wonder.

Cheers,

Don

 

Thanks Don, the X300 comes with the spring clamps.

Glad to hear that 5/8" is the size. That saves me a little time.

If heat is the issue, maybe I'll put some heat shield wrap on those two hoses. I have some that is made to slip over hoses left over from a fuel injection project many years back.

That write up is fantastic, and goes to show how great these forums are for owners!


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My X300 XJR power steering low-pressure return hose leaked from the crimped fitting at the cooler end. I had a hydraulic hose shop cut the crimp ferrule off and fit a new piece of hose and re-crimp it to the cooler fitting. The old one was 12mm hose. The new one is 12.5mm because that's what the shop had on hand. It is not leaking yet.
The pump feed hose from the reservoir also leaked at the pump and made a big mess; trans fluid spreads everywhere! A new screw-type hose clamp did not fix the leak. I put on a new hose, with the old spring clamps, and its not leaking so far.
The original hoses could have been 20 years old, so I guess its no surprise they are going hard.

 

Any idea if the pump->reservoir hose is 3/8" or also 5/8"? (I can find out later, but just came to mind and I'm not currently under my hood )

Also, do we know if our reservoir has a built-in filter/screen as shown in the following thread:

Recommendation to clean your power steering fluid reservoir circular wire mesh filter - Bimmerfest - BMW Forums


Our reservoir is of a similar type, so just wondered if we knew.

If not, I may fit a filter to the low pressure pump->reservoir hose, but most PS filters are 3/8" hence my question about hose size.

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I don't know if it's relevant or not, but possibly no harm to know. I was recently chasing down a power steering fluid leak and sourced it to a fitting at the steering rack. A little tightening and the problem seems to have been sorted. But while poking about, I noticed that the two hoses from the reservoir were chaffing/wearing against each other where they made contact. this slight wear was concealed at it occurred where the two hoses sort of crossed over each other.

Any leak from this point would have become apparent in time, depending upon how clean things were in the first place. There is, or should be, a small plastic clip arrangement that fits onto both hoses and keeps them apart. Might be worth looking into as a possible cause of a minor leak.

 

Thanks, I plan to sleeve both supply & return hoses in aluminized fiberglass heat shield fabric as well. So maybe that will help.

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Replaced the power steering low pressure supply ("suction", reservoir to pump, MNA3980AC) and low pressure return (cooler to pump, MNA3990AC) hoses today. I used a heavy duty plain 5/8" hydraulic hose for the MNA3980AC which is less than $5 versus the non-too-special $25-60 OEM hose. The replacement MNA3990AC return is a Eurospare, so we'll see how that works out long term. The OEM was twice as expensive at $100.

I added aluminized fiberglass hose heat shield to to both hoses to see if that helps them hold up better, especially the supply/suction hose which runs close to the exhaust manifold.

Also got new OEM hose clamps, one JHC302230 for the return, and two JHC301220 for the supply/suction. They were really cheap, so I thought new clamps were inexpensive insurance while replacing the hoses.

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Replaced the power steering low pressure supply ("suction", reservoir to pump, MNA3980AC) and low pressure return (cooler to pump, MNA3990AC) hoses today. I used a heavy duty plain 5/8" hydraulic hose for the MNA3980AC which is less than $5 versus the non-too-special $25-60 OEM hose. The replacement MNA3990AC return is a Eurospare, so we'll see how that works out long term. The OEM was twice as expensive at $100.

I added aluminized fiberglass hose heat shield to to both hoses to see if that helps them hold up better, especially the supply/suction hose which runs close to the exhaust manifold.

Also got new OEM hose clamps, one JHC302230 for the return, and two JHC301220 for the supply/suction. They were really cheap, so I thought new clamps were inexpensive insurance while replacing the hoses.

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