frequency to change hydro oil / filter but only average 70 hrs a year? Still yearly?

Fact: Hydro-Gear recommends an initial filter AND OIL change at between 75 and 100 hours and every 400 hours thereafter for their ZT-2800, ZT-3100, ZT-3200 and ZT-3400 transaxles.

Fact 2: For all Bob-Cat zero-turn mowers "the transaxle / pumps / wheel motors will have a 2 year warranty which can be extended to a 3 year warranty, provided the product is within the warranty period and if the hydraulic system is maintenanced at the required service intervals by an authorized BOBCAT dealer in accordance with the requirements stated in the manual."

It says that the service needs to be completed by an authorized dealer to extend the warranty from 2 to 3 years. For me that meant having the initial service done by my dealer before I hit 100 hours. Cost was approximately $200.

My thoughts regarding hydros are similar to my thoughts relating to engine air filtration systems. DON'T OPEN THE SYSTEM UNLESS THERE IS A REAL NEED TO DO SO. Every time you crack open a cap and expose the unit to the environment you risk introducing contamination. This contamination is often the direct cause of failures. It would therefore have been better to just leave it alone. Even if you try to clean the cap and the plug holes ahead of time there's usually some grit embedded on the threads and around the entry point if you just wipe it. Don't just wipe it off with a rag. Wipe it and wash it. Make sure that it is absolutely clean! The whole process should be done in a clean dust-free environment. Pretend you're a surgeon. Take your time! Yes, there's an inline filter, but the damage done by the contamination getting through the unit to the filter will still occur and is permanent.

What I'm saying is if you're going to hastily service/check your hydros and not pay extraordinary attention to not getting ANYTHING foreign into the unit, don't touch it. Your good intentions are more likely to ruin your hydros than prolong their life.

Other causes of hydro failures are not keeping the unit clean causing overheating, operating them with the mower at low engine speeds, and pushing/pulling/towing the mower without disengaging the hydros. Abuse as well. I'll bet more hydros are destroyed by the above reasons than lack of service.

It's also a good idea to give your hydros a rest now and then, especially during heavy use in hot conditions. I try to idle down my mower and take a water break for 5 minutes every hour or so to let things cool off when I'm mowing my back acreage in the summer that takes about 5 hours.

Wouldn't it be nice to have a transmission temperature gauge display on the hourmeter?

I guess I'll never find out why someone would service their hydros annually yet recommend to never drain the oil unless a repair is needed. Makes zero sense to me. That's like changing your underwear every day but never washing them. :laughing:

Darryl G said:

I guess I'll never find out why someone would service their hydros annually yet recommend to never drain the oil unless a repair is needed. Makes zero sense to me. That's like changing your underwear every day but never washing them. :laughing:

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I could not answer why the manufacturer would recommend this, but it makes sense to me that the manufacturer would only want you to remove as much fluid necessary to do the filter service. While replacing fluid that has experienced some degradation/decomposition, it is the filter that removes the particulates. So long as you do not introduce any contamination into the system, the fluid after the change will be cleaner than before it was serviced. Also, if all of the fluid was drained, which I believe you would have actually siphon the system, you could then introduce air into the motors which would otherwise be primed if the filter alone was removed. If a problem arose from air being introduced into the system by mistake, you would likely end up with a disgruntled consumer who then has to get professional service for something that they themselves should have been able to do at home.

Again, I do not have the answer but I did pose this question to a mechanic that services hydraulic systems on large manufacturing equipment and he mentioned the risk of cavitation in the pump if you cannot properly remove the air. I don't know if this would actually happen but if anyone out there has made it a habit of completely removing the fluid while doing a filter change and top off, I would appreciate their input on this. I simply follow the Owner's Manual.

I will add my 20¢ worth.
When I do a tranny oil change I soda blast around every where that I will be removing a filter or plug .
This is preceeded by a strong blow dawn with the long handle air duster running at the max pressure my compressor can pump out , 180 psi of the entire area
Then after the soda blast they get a pressure wash then a blow dry then they sit for at least 1/2 day to make sure everything is clean & dry.
After that it is as per tranny makers instructions re quantities & purging & topping up.
A consideration that few owners take into account when they purchase their machines.
A remote reservior and a remote filter make this process really quick & easy.

On the Cub Cadet tractors I drop the tranny all together so it can be cleaned properly before removing the oil filter.
This also allows the oil filter to be pre filled if the tranny is rotated 90 deg.
The tranny then gets its purging & topping up before it is replaced in the tractor.

You can never clean the work area enough.
A tiny amount of dust can trash the hydros in no time flat.

SO if you can not be bothered to clean the area properly don't change the oil.
The life of synthetic oil in a hydro box is almost forever the only reason for changing it is removing the wear debris.

bertsmobile1 said:

The life of synthetic oil in a hydro box is almost forever the only reason for changing it is removing the wear debris.

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My Exmark used to require Mobil 1 15W-50 in the hydro system but no longer does Exmark recommend use of this oil. Something changed in the formulation of Mobil 1 so Exmark now sells their own hydro fluid that contains the proper chemical formulation/additives. I think it was Zinc or some other mineral in the oil that the hydro system benefits from but regulations don't allow for this to be used in "on-road" vehicle oils anymore.

Also, I know that the filter used in my system is bi-directional. This is not a gimmick, because I have seen these types of filters in industrial applications. Anyway, between the cost of the filter and fluid, we have a $60 annual hydro service. Steep but beats burning up EZT's every couple of years.

cruzenmike said:

My Exmark used to require Mobil 1 15W-50 in the hydro system but no longer does Exmark recommend use of this oil. Something changed in the formulation of Mobil 1 so Exmark now sells their own hydro fluid that contains the proper chemical formulation/additives. I think it was Zinc or some other mineral in the oil that the hydro system benefits from but regulations don't allow for this to be used in "on-road" vehicle oils anymore.

Also, I know that the filter used in my system is bi-directional. This is not a gimmick, because I have seen these types of filters in industrial applications. Anyway, between the cost of the filter and fluid, we have a $60 annual hydro service. Steep but beats burning up EZT's every couple of years.

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Oh, now I get it. Sorry, didn't realize you had EZT trans on that machine. I know the later ones have HG pumps and wheel motors. They must have upgraded the hydros on newer models.

Darryl G said:

Oh, now I get it. Sorry, didn't realize you had EZT trans on that machine. I know the later ones have HG pumps and wheel motors. They must have upgraded the hydros on newer models.

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No, I have Hydro-Gear pumps and Parker/Danfoss drive motors. I was simply making a statement regarding the added expense of servicing a system like mine beats having a relatively non-serviceable system like EZT's which would fail in less time.

cruzenmike said:

No, I have Hydro-Gear pumps and Parker/Danfoss drive motors. I was simply making a statement regarding the added expense of servicing a system like mine beats having a relatively non-serviceable system like EZT's which would fail in less time.

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Ok. Bert goes into detail about how important it is to not introduce contamination into the system during service and the lengths he goes to in order to prevent it. That was my main point here - that servicing them could actually do more harm than good and why mine don't get serviced unless necessary. Different strokes for different folks. :smile:

Darryl G said:

Ok. Bert goes into detail about how important it is to not introduce contamination into the system during service and the lengths he goes to in order to prevent it. That was my main point here - that servicing them could actually do more harm than good and why mine don't get serviced unless necessary. Different strokes for different folks. :smile:

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More like, pick your paranoia; premature failure from lack of service or contamination from doing any service at all!

Yep that was the whole point.
Some are really hard to get at and even harder to clean.
An inital early oil change is important because the highest rate of wear in during break in.
After that the less you touch it the better.
If you have an external filter then change it at the hourly interval specified by the maker
Hydros are the one thing where less maintenance is better due to contamination possibilities.
The oil will last forever all you are doing is removing the wear debris and wear debris is directly proportional to hours of use.

The caveat to that is water condensing inside the trans which will cause the oil to deteroriate.
So if your engine oil goes milky during the off season then you will need to change the oil a bit more than at the hourly intervals.

It is the same as fuel going off.
A lot of it has to do with your local enviroment, where you store the mower and how long an average working session is.
The factory can not account for all of these variations in use.

So if you were one of my customers, I would change your oil at the beginning of the second season so I can see what the oil looked like after storage.
From there I would check the makers recommendations and sort out a schedule for you.
If your oil came out crystal clear then it would be at the maximum hours ( or even higher ) .
If it came out grubby & milky then it will be annually, at the beginning of the season to get rid of the condensation of the off season storage.
Unlike engine oil, where you have the combustion contaminants changing the chemistry of the oil , and additives that react or just plain oxadise plus the effect of very high temperatures.
The only thing that causes tranny oil to deteriorate is water from the air inside the box, other than that is has an easy life