Changed coolant and thermostat…now overheating.

[MJE]

New machine (Hitachi ex120-3) and today I changed the coolant and thermostat….now it is overheating after about 20 minutes of operation. maybe it was doing this before but since it is new to me I am not certain. Any ideas on what to check. Half tempted to put the old thermostat back in…I, tested it and it works with no issues.Other ideas?

 

[ianjoub]

make sure radiator is clean, fan motor is spinning correct speed

Is there an air bleeder valve on the cooling system? Maybe you have an air pocket.

 

[1693TA]

If your radiator filler neck is not physically higher that the top of the engine there is a good probability you have an air lock as mentioned. Usually an overnight cooling after the engine has been brought up to temperature will break this, but not always.

I've seen more than one new thermostat not perform correctly out of the box.

 

[Delmer]

Use a non contact thermometer to check the temperature of the thermostat outlet to the radiator, and the water pump inlet from the radiator, and the block or head, all while it's overheating. Those temps will give a good idea what's going on.

Is it losing coolant? or just getting hot on the gauge? or what?
Have you cleaned out the radiator? first thing to check on any ag or construction overheating is the radiator plugged with dirt. it's not clean unless you can look through it with light on the other side and see it's clean.

 

[Bumpsteer]

I've found replacment t-stats to be the most unreliable part on the planet.....even from the dealer.

Ed

 

[mukeshcat]

Put new thermostat in boiling water externally and check if they are fully opening ?

 

[MJE]

Update…installed old thermostat that was working after testing in boiled water, put 2 bottles of VP Racing cool down in radiator, cleaned radiator, ran heater for a bit while idle. Expansion tank not losing fluid. Still overheating. Could the cap cause issues?

 

[Delmer]

The cap is one of the last things I'd expect to cause this issue. Still need to know what it's doing, getting hot on the gauge? bubbling? steaming? what actual temp is the block?

 

[MJE]

Delmer, thanks for the reply. Gauge does not appear to be operational as it shows no movement. A warning light and buzzer are the only indications of overheating. No bubbling, no steaming. The hoses top and bottom get extremely hot, to the touch. I will have to get a way of measuring the temp. Aside from the warning light and buzzer there is no other indicators of overheating.

 

[Allan M]

Came across this video a while back while researching an overheating issue on a tractor. It didn't apply to my situation. Although this is a much smaller machine than yours it might be related.

Best, A

 

[MJE]

Allan, thank you for the post. I removed the belt this morning from my machine and have no movement in the crankcase pulley. my fingers were crossed hoping the was it.

While pursuing Allan’s suggestion I rotated the water pump pulley and there is a faint whining sound when rotated. This whining sound was in both directions of the pulley’s rotation. Is this normal.

I acquired a infared gun and ran the machine to the point of getting the warning light and buzzer…below are the readings.

activation of warning light/buzzer Pre light/buzzer
Thermostat (T). 200 180
Top hose 188 166
Lower hose 174
Expansion tank 102

 

[ianjoub]

^^^^ That sounds like a bad temp sender.

 

[Allan M]

There are definitely Hitachi owners and mechanics on this site. I hope these guys chime in soon. Occam's Razor: "All things being equal in complex systems the simplest explanation is usually the explanation." I also think that if you eliminate the obvious that which isn't obvious becomes visible. As an example, my mother-in-law called the other day. Her car wouldn't start at the grocery store parking lot. She had a new battery installed just a week earlier. She could enter the car, power up the radio, lights, windows, etc... I was thinking bad solenoid, ignition switch, starter, maybe loose new battery connection...but the simplest explanation? Key FOB battery too low to disable security system so car could start but enough juice to shut off the other car security so that she could enter the car and run windows, radio, lights, etc... I just lucked into this solution. I told her to try her duplicate keys. I wasn't thinking about a low FOB battery...but when the car started I put the logic together. I'm wondering in your situation what is the trouble shooting protocol? The cooling system isn't that complex relatively speaking (although the Hitachi crankcase belt clutch in the video I sent you was new to me): radiator cap that doesn't hold pressure, sensor as ianjoub points out, thermostat or thermostat installed backwards (see this on a car but that was years ago), bad water pump (sounds possible), coolant can't be an issue, fan belt skipping/too loose to circulate coolant, I don't think leaks are an issue. Again, it would be terrific to hear from a Hitachi mechanic on this one. I'll bet on a bad water pump if it's making noise. Good luck, A

 

[MJE]

Update: Ianjoub made a point about ensuring the radiator was clean. While we took a water hose and air gun to it, I was not confident that the back side of the radiator facing the oil cooler was completely clean. Today we pulled out the radiator….nearly half the radiator facing the cooler was covered in thick oil and dirt. After washing and blowing it out we put it back in and refilled it and ran the machine. The radiator temp was in the range of 150 degrees with the hose temps significantly lower. I won’t be able to run the machine hard until another few weeks but I believe the problem may be solved…dirty radiator! I also tested the new thermostat and reinstalled it. It has a burp hole in it that may also help with airlock. Thanks for all of your help…I will update if the problem resurfaces.

 

[Swetz]

covered in thick oil

I would investigate the source of this or you will be back to overheating in the future!