656 temperature

I have a 656 gas that has perplexed. When I start it the temp gauge goes to full hot pegged in about 3 to 4 minutes. I have replaced pump and thermostat but still no luck. Do the temp gauges go bad? Any way to check it?
Thanks for any suggestions.
Tom

Temp. gauges can go bad but I would use a temp gun and check to make sure .

I think you'd see water boiling out if the gauge was accurate.

Most likely a bad temp sender (I've had 'em fail exactly that way on a couple different tractors).

Quick test: Run the tractor until the gage pegs hot. Now disconnect the wire at the sender. If the gage drops back to cold with the wire disconnected the sender is the problem.

Does your tractor have an aftermarket temp gauge? The original gauge would be a mechanical one in the cluster with the fuel gauge. If you have the mechanical gauge the most likely cause is going to be a compression leak into the cooling system.

When you first start the tractor the thermostat will be closed preventing any circulation through the radiator. The exhaust gases from a compression leak will collect at the top of the head where the temperature sensor is located while the coolant is displaced into the radiator through the lower hose. Without the sensor being submerged in liquid coolant the temperature of the exhaust gasses can quickly rise causing the rapid movement of the gauge.

SAll good ideas..thanks! More question please? Where does the probe mount? I am not sure where it is? Can I buy just a probe? It is a fuel amp oil temp cluster gauge. I will check temp with a gun...where should check it?
Thanks again I appreciate the help.
Tom

Have you taken the cap off cause in just a couple of minutes it cant be boiling then take a temp of the coolant

If you have a triple gauge set then the probe/sensor is most likely a mechanical capillary type that consisting of a metal bulb with a fine tube protected by a continuous coil of wire surrounding and protecting the tube. It should lead from the bolt on metal adapter on the side or in front of the block with a hose leading to the radiator.

You can take a non contact reading directly from the coolant with the cap removed. Make sure you remove the cap with the engine cold.
If it is a pressurized system a few minutes with the cap removed should not hurt it and will allow you to simultaneously look at the gauge and measure the coolant in the radiator filler neck and compare. It might be somewhat cooler because the thermostat probably will not have opened up at that stage. The main issue here is safety. Scalding coolant is no joke. Ask me how I know.

The best and safest way to check it is to remove the probe and stick it in a pot or cup of hot water and check the gauge. You can simultaneously check the temp in the cup with your non contact infrared sensor or a simple high range thermometer.
You don't have to remove the gauge or capillary tube. Just stick the probe into the cup. You should have enough flexibility to move the capillary to a cup adjacent to the housing. Since it is mechanical it will work with no power.

I forgot to mention. When you remove the probe from the housing be sure to use a wrench to keep the probe from rotating as you loosen its collar. Twisting it will fatigue and break the capillary tube. Then you will need a new gauge set. Sometimes a probe and capillary can be replaced if you can reach the connector where it screws into the gauge. If the gauge itself is bad then the entire cluster has to be replaced or you can get an aftermarket gauge or an electric gauge with just a wire and no capillary to break. If the wire breaks it can easily replaced.

Please share your findings....Owens explanation(hypothesis) has me worried for you. I would like to know the outcome as it is good learning material here. Thanks

Chance

OK here is why I did. I found the probe I think but it is very tight behind the intake exhaust manifold and not very accessible. I topped off system with water and closed up cap. Started her up and at half throttle in 3 minutes was pegged on H. I used IR temp gun and read temp in several places. 170 was top temp after 10 or 15 minutes. I now feel systems good and probe or gauge is bad. Looks like a real chore to get at the probe so I will drain and refill with proper mix of antifreeze.
That is what have to report.
Comments welcome
Tom

A candy thermometer Will work for a temp test to compare with the gauge in the tractor. Can just stick it in the cap and see what it reads.