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Old 07-24-2011, 09:33 AM   post #1 of 1
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Default Oil temperature Gauge and Sensor install - with lots of pictures

This guide is showing how to install an electric oil temperature gauge and sensor on an air cooled engine. It specifically shows the installation on a 1999 Simplicity Legacy with a CH25 Kohler Command engine, but the principles will be similar for other tractors.

I started working on this as I have a Simplicity Legacy tractor with the Kohler engine. Since I don't have the luxury of a liquid cooled engine, I have no indication of how hot these engines run. It seem pretty hot when I am done mowing the lawn, but any air cooled engine does typically run kind of warm. I have wanted to install an oil temperature gauge for some time now and I finally found one at a price I could not resist.
It did take quite a bit to install it on the Legacy since you have to lift the engine out to get to the oil drain plug. Well at least tip it up, but since I was going at it I took it out all the way to give it a good blowout under the shroud. It was actually very clean so it wasn't needed - but better safe than sorry.
The installation will be a lot easier if you can access the oil drain plug on your engine.

Here is the guide to how I did it:

Here is the gauge I got. yes, I know Harbor Freight is questionable quality. But I actually hooked it up inside and put the probe in hot water. When I measured 184 F with my digital meter this one showed just under 180 F. So close enough. And with sale and coupon it was $ 9.00 (tax included)

These are the parts you get. Only downside are super thin wires on the gauge.

The first step is to remove the spark plug wires and the negative connection to the battery. Safety first

The sensor is 1/8" NPT while the engine plug is 3/8 NPT. So you need an adapter to install it.

Remove the two bolts and hooks holding the hood

Remove the hood

Then remove the PTO tension spring - it helps to have a real spring puller. But in a pinch a piece of wire will work too.

Remove the PTO belts. Remember to mark them first so they can go back on the same way.

Remove the drive shaft. This is kind of awkward to get to, but it is possible.
It really helps to have a hex key socket for the wrench (in this case 6 mm). The screw driver is for holding the drive shaft so it doesn't rotate when you try to loosen the screws.

First you have to remove the screen

Then remove the 4 bolts holding the drive shaft. You could move the engine forward before you remove these, but I think it was easier to take them out so to not disconnect the drive shaft from the hydro.

Remember to disconnect and plug the fuel line.

Unplug the electrical plug on the engine

Unplug the PTO clutch

Then remove ground cable, solenoid cable and power cable for the starter.

Disconnect the throttle and choke cable. If you mark them first it will be easier to re-install them in the correct position again.

Then remove the 4 bolts holding the engine to the tractor

Finally here is the engine out of the tractor. Note that I left the oil drain on the tractor as it is very difficult to get to on the Legacy. This means that you have to be very careful when lifting out the engine and setting it down – you want to make sure you don’t break it off.

I removed the unused oil drain plug and inserted the adapter. I put it in first so I could use a torque wrench. It would suck to strip out the threads. I torqued it to 10 ft-lbs per the engine instructions for the drain plug. I used Teflon tape on the threads to prevent leaks.

Install the sensor. I also used Teflon tape on the threads here and screwed it in tight. I made sure that I did not start spinning the bushing as I tightened.

Then I turned to the tractor itself and worked out where to put the gauge. There was really only one option - so that is where it went. I always think it is scary to drill a big hole in a tractor
But I had checked that a new plastic dash was only $ 35 if everything else failed.

Then I completed all the electrical connections. This was the most difficult part because of the very thin wires. And then trying to mate them up with the oversized fuse holders. I grabbed the power from the light switch. There is one power feed going to the switch and one leaving it that is hot when lights are on.
Here is a modified print of the gauge wiring. The constant hot listed is only to remember which color back light was selected on the gauge. It defaults to a pleasant color that matches the current dashboard. So I just tied it into the switched hot lead.

It is difficult to take good pictures of the wiring. But here is the end results.
You can see the gauge in the background all installed with the bracket and the two fuse holders on the right

Drivers view of the gauge installed

I used the tractor for driving the cart around a little as I had to empty the kiddy pool. I pump it into the cart and then use it to water the trees. I just use a 12V bilge pump which pumps out 75 gallons in just a few minutes.
Anyway as you can see the oil stabilized at only 160F.
Much lower than I expected so I guess the oil cooler really does work. The Legacy is also using and extra fan in the front of the engine to help cool it better than just the built in blower on the engine.

Here is a picture of the gauge at night showing the default color lighting in the dash. It is not too intrusive or blinding.

I later mowed the lawn with the tractor and the 60” tow behind mower (4 acres so about 1 hour 45 min). The grass was relatively short, but it is still a good workout for the tractor pulling the 500+ lbs tow behind. The oil temp stabilized just below 210 F which is very reasonable.

On another post someone had measured the oil temperature on a new Kohler Command engine after working it hard and had found about 250F. That engine did not have the oil cooler like mine has.
Kohler does advertise that the oil cooler reduces the oil temperature up to 40 F, so I guess they are correct in that statement.

If I had to do it again I would probably solder up the wiring harness on the bench first. That would make it easier than the crimp on connections on those thin wires.

All comments and questions are welcome. I will do my best to answer them.

Alan Lloys is offline   Quick reply to this message
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