Hydro temp light

[Dieselcowboy 210]

Why would my hydro temp light come on and stay on after mowing for awhile? I just did a filter and fluid change with full synthetic. Tnything I can do other than unhooking it? the trans case was really kinda hot enough I did not want to keep my hand on it very long. This is in a 520h

[gwest_ca-(File Mod) 11,433]

From the Demystification Guide page 3-38

Switch # 113193 is designed to close at 200 degrees F.

Normal oil temperature is 180 degrees F.

[zieg72 209]

Make sure the fins are not caked up with gunk.  My 97 use to temp up when it was hot after a long run until I blew all the gunk out

[Dieselcowboy 210]

I just bought this one and I have givein it the works wash and cleaning before the first run. Everything around the trans is red again.

[312Hydro 474]

Check the fan on the tranny. The center bolt may be loose allowing it to freewheel.

[Dieselcowboy 210]

Could the sensor be faulty? If the fan, oil, filter, and clean housing there is not really a reason to overheat on normal mowing right?

[Dieselcowboy 210]

OK I mowed today until the hydro temp light come on. I brought our heat sensor home from work ( It has a lazer to point and sense). I hopped off and tested the trans case it was reading 120 degrees and the hydro filter was reading 130 degrees. I read somewhere on the forum that the hydro sensor is suppose to trigger at 200 degrees. Is that right?  The engine oil filter was at 160 degrees. So I might be a sensor issue anyway.  Anyone have ideas with this info on hand?

[zieg72 209]

The sensor is touching the oil so I would say it is a faulty sending unit

[Dieselcowboy 210]

The sending unit being the sensor itself ?

[Hodge71 665]

The sensor is the bimetal thermocouple type. My understanding about it is that the 2 different metals expand and contract at different rates. This one is calibrated to close at 200 degrees allowing voltage to travel through and to the light causing it to illuminate. ANything under 200 should keep the light out. All you should need is a new sensor

[Save Old Iron 1,571]

Before you spend time searching for and invest money on buying a new sensor - remove the sensor and measure the contact resistance at room temperature.

 

Place the temp sensor in water at about 170 or so and the resistance should be the same as room temperature. Increase the temp of the water until just before it boils. The temp switch resistance should now have toggled to opposite of what room temp was. If it was an open circuit at room temp, the contacts should be shorted at over 200F.

 

Somewhere between 180 and 200F, the contact resistance should toggle. If the change happens in the range of 130 - 140F range, replace the switch.

[MalMac 1,332]

Like said If you can test temp sensor. I did have one go bad and replace it. Expensive little dude.

[546cowboy 302]

With the temps you listed I would say it is the sensor and the easiest way is to find a used one and replace it. When the light comes on does it go off if you put it in neutral and let it idle for a minute? I had one do that a couple times. That was after 2 hours of mowing with a 60" deck.