Why Do Hydrostatic Transaxles Get So Hot?

Friction creates heat. Fluid under pressure, being forced through restrictions, is subject to friction losses and pressure losses, generating heat as a by-product. All the moving parts also are subject to friction losses, which also generate heat. The heat you feel is directly related to the efficiency losses in the transaxle. Check your fluid quality & quantity. Check any filters that may be restricting oil flow to the transaxle. Are any heat exchangers installed in the system? The heat can also be created from the transaxle being overworked by other components in the system that are not operating properly.

Ditto to what RVZ717 said. I would also add that the units should be kept clean. Dirt and debris stuck to the casing and cooling fins prevent heat from being transferred away.

The design of the machine the hydros were put into can also be a factor. In other words, is the machine around the hydros designed to provide sufficient air movement and cooling or does it hinder the fan's performance.

this all explains the problems with this transaxle and how it is fitted to a ride on mower, which gets very dirty and is quite difficult to clean completeely once all the implements are fitted. i am thinking that it has got too hot, over a period of time, and this has affected the moving parts, maybe warping them, so they dont move properly.

i have it in bits, but it looks ok, will take the gear bit to pieces and see if they are warped or broken.

but i see now how with it being covered in mud and grass, this would affect its heat transfer, so in the future if and when i get it going again, i will keep it very clean and maybe fit a new fan on rebuild,

thank you

Keep in mind that if this has a lot of hours on it, say more than 500, the parts may simply be getting worn. Depending on the application, those units can have design lives of anywhere from 500 to 2000 hours. Even though the parts look good, they may be worn past their optimal tolerances. There may be some seals that are worn as well. Between the hydraulic components and the mechanical components, the efficiency losses are enough to noticably affect the performance. The greater the inefficiencies, the greater the heat buildup. On the plus side, the unit is probably rebuildable.

yes, this is what the garage said, but they said it couldnt be fixed and had to be replaced, which is a terrible waste. imainge if everybody just replaced all the time.

so i am determined to try my best to fix it, i dont think the transmission fluid hadever been changed. at least not by me, i have only used the machien for ayear, but i wasnt the first to use it.

so when i get in and look at the seals, also the shift key maybe worn, if i am lucky i can replace them for new ones.

but it first lost power going up little hills then lost power completely, but omly going forward, would go back wards fine, so i figured the forward gear or shift was worn out, any way thanks again, i will post agin whe i have a new question. ta

Hydrostatic transmissions tend to be very inefficient. Back in the 1960's I tested a variety of hydrostatic transmissions for lawn tractors as GM was looking to put a hydrostatic transmission in a Cadilac. The best efficiency was 75% at a 1:1 ration on an International Harvester cub cadet. That means a lot of heat is produced when operating a hydrostatic transmission, especially when operating at a high reduction ratio.

this is very helpful, and explains the problems with transaxles on ride on mowers, s they get very dirty and are quite hard to clean properly when they are fitted with their implements. so this dirty cover on the casing would affect the heat transfer and so keep it too hot, thus affecting the quality of the transmissoin fluid. sometimes eople change the fluid and it fixes the problem.

again thank you

Since you mainly use the mower in hot weather, if it was my unit, I would fill the transmission with 10W40 or 20W50 Multi Viscosithy Engine oil when you put it back together. Engine oil is designed to operate at elevated temperature and the Multi Viscosity stuff does'nt thin out so the efficiency stays up as heat builds.

Had a neighbor do this and kept his mower running almost full speed capablity two more summers.

Even Vickers and Eaton recommend Engine oil as a suitable replacement for Hydraulic oil and several mobile equipment operators locally use engine oil in all their hydraulic circuits to eliminate the chance of someone putting the wrong oil in the wrong equipment.

I would be cautious about putting an entirely different type of oil in the transmission. It may perform better for a while if it is all worn out inside, but unless the oil is recommended, I wouldn't do it unless you just want to get by for a while longer before replacing the entire unit. No offense, but I would regard Bud's tip as a last resort before having to replace the unit, although it may be enough to get you by until a more opportune time for replacement.

Another resource you might check is www.lawnsite.com. There is a mechanics forum on there where there are a lot more people that have actually worked on these things than probably what you'll find here. There are a lot of good people there too.

thanks for the link to lawnsite, i have joined and met some liek minded people who are very welcoming, so i should get some advice on the subject as the amchine i am fixing is american and most people seem to e american.

thanks again for that,

but i will still comecaxck to cr4 for technical questions

jay

i put it all back together, replaced the fluid with new and now it works fine, in fact i think i could have saved a

lot of time and just replaced the fluid, haha

Hey, good for you. The grass must be quite high by now. It will get a good workout cutting it. What did you use for fluid? Is the fluid available in a synthetic version? Have you incorporated a filter into the transmission?

If heat build up is a concern, plumb a spray nozzle from a pressure cleaner, or something similar that will spray clean tap water in the unaccessable areas. Then just connect the nozzle(s) to a garden hose fitting and flush it when done using the mower.

Again, nice work.

hi ,i replaced it with fluid that was recommended by the manufacturer,its wasnt cheap, but it worked, of course i have not had this problem since, as is typical, but thanks for all the advice anyway

Glad to hear that putting in clean, correct oil helped. The manufacturers usually have good reason to specify a certain oil, and sometime genuinely do have their own oil specifications that are better than other products on the shelf. They usually charge accordingly, but is justified through the performance.

im sure if the previous users had maintained the transaxle/ride on properly this would never ahve happened, as all the other parts are a it worn from tkaing the strain