The history on my mule is that it recently overheated due to a bad water pump and it also got hot enough to melt the edges of the plastic valve covers and ruined the thermostat as well in the process). The repairs I describe below got my mule running like new again for a little easy labor at a cost of approximately $125 with antifreeze.
I did have someone else do the water pump first so that cost is not included. What I have learned is that if your valve covers melt everything else can be ok but the engine getting air will cause the mule to run really rough, like when your head gaskets are bad and it will blow black smoke out the tailpipe until you replace the covers. I initially thought the engine was done. Again don't assume the head gaskets are bad. Here's the step's I followed to get my mule running like new again.
Hope it helps someone else with similar issues.
1) Flush the radiator and replace replace a leaky water pump, if necessary, (again don't assume head gaskets are bad) these things are tough.
2) Check valve covers. If the edges have melted do to overheating buy new ones online (don't be cheap and put sealer on them) with metal gaskets (OEM covers and gaskets approx $50 on amazon) and replace them.
3) If you have been blowing black smoke change your air filter (non OEM $14 on Amazon) its probably clogged from the oil fumes.
4) Replace the thermostat (OEM $20 on Amazon). There are Youtube videos for this. Its a little messay but easy.
5) Refill antifreeze and jack the front of the mule on some ramps or park on the incline of a hill and unscrew the purge valve screw on the rear passenger side
of the engine near the main antifreeze line to let air out of the system when the engine is cool.
6) If you were blowing black smoke change the spark plugs (never hurts).
7) Start the engine and try it out. If you were blowing black smoke give it a few minutes to clear out any residue left in the system and don't assume its not fixed right away. If the valve covers were the main issue it should be running much better right now. If it won't start make sure you replaced the air filter its probably clogged.
Note: If your valve covers are good you can buy a head gasket test kit on Amazon to confirm whether the head gaskets are blown for appoximately $39.
If your Mule is not running rough but just overheating I would replace the thermostat to make sure its not bad and flush the antifreeze and purge air out of the lines by lifting the front end of the mule in the air (with ramps or parking on a hill) and opening the purge valve while the engine is cool and then lower it back down and top off the levels in the radiator and reserve tank to make sure there is no air in the coolant line.
Other tips for 3010 Mule maintenance
Here's a few other tips for keeping your Mule running good for a long time:
1) Grease you carrier bearing regularly. It is a bear to reach the zert without removing the floor cover which if you have a older mule can be a lot of work.
What I did was bought a 90 degree zert attachment online and attached it to the zert on the bearing and because the connection was so tight just left it for greasing the bearing again later.
2) After greasing it go out on a straight runway and drive it in 4 wheel drive for a few minutes to work the grease in.
1) Tire pressure is huge when using 4 wheel drive. You mule will ride much better if you follow the book and put 24 lbs in the rear tires and 10 lbs in the front tires. The steering wheel will also stay straighter in 2WD if the tire pressure is correct.
2) When switching between 4WD to 2WD stop and go into reverse if needed to complete the switch.
Horn not working (Try not to get the steering wheel wet it will cause the plate on the inside to rust)
1) Check the fuse under the seat
2) Remove the horn fuse and pull off the center cap and the inside plastic housing and if you see rust around the center ring at the top of the steering wheel sand it off or use a flat head screwdriver
to scrape the rust off. Re-install the plastic insert and cover and replace the fuse and you should be good. You might have to hit the horn button for a few minutes to get things working spot on again.
Oil in the Air Filter
Make sure you didn't overfill the oil when changing it. If you did empty some out and replace the air filter
Bad front boots
1) Don't let this go. Get new covers put o ASAP or have the CV joints replaced ASAP. I had someone else do this for me.
Regular maintenance (follow your owners manual obviously-these are just what I do).
1) Change oil every year and oil filter as needed.
2) Change air filter every year.
3) Clean drive air filter (wash yellow foam cover in soap and water and rinse with water and let dry and blow air filter with compressed air) or change it out if needed ($17 online).
4) Check transmission fluid every year and follow regular maintenance for flushing it.
5) Change fuel filter every 2-3 years as needed.
6) Change spark plugs every 1-2 years as needed.
7) Check and top off (if needed) antifreeze.
8) Put a trickle charger on you battery when you park it for long periods of time.
9) Put Stabil in your gas when parked for long periods of time as well.
10) Check front differential oil every couple years and replace the fluid according to schedule (I use Royal Purple oil)
These maintenance tips are all quite cheap and will keep your Mule running much longer with less repairs
(especially the carrier bearing greasing). My Mule is now 15 years old and runs as good as the day I bought it so
I hope these tips are helpful to others on this forum. "Enjoy the ride".