Cat excavator water temperature gauge in cab goes to red; using a temperature gun, reading of top of radiator was 150F, top water hose at 140F. I checked the wiring at the temp sender did the disconnect wire from the temp sender; open = low, grounded wire to the machine = gauge went to full red. Installed a new CAT part number 094-5966 temp sender. After a couple mins (5) the gauge went to red. After the new sender installed and engine run 5 mins, temp top hose was 140F, bottom hose 124F, top radiator 150F. Machine Caterpillar E120B Serial Number 6JF00719 Engine 3114 Any idea as to what to do next to fix the temp gauge in the cab?
Did you Teflon tape the threads on the sender?
I’m guessing the sensor is a single-wire type. If you pull the wire off the sensor the gauge should go to zero/minimum. If it doesn’t my bet would be that it is shorted to ground somewhere between the gauge and the engine.
Did not use tape used paste
It is a single wire I pulled the wire off the sender and it did go to zero, I grounded the wire to frame and the dial went to red.
I asked because, tape and paste can interfere with the grounding of the sending unit. The threads should be dry. I’m just sayin’, check the easy things first.
Need to ohm out the new sender from post to body and body to ground, both cold and hot. Also, be sure your connector isn't bottoming out and touching the body.
Those temperatures are getting awful close to what we would suspect a plugged radiator I think I would start by cleaning rad externally
Shooting temp at sender maybe interesting if accessible.
It had teflon tap on it, I used paste for the new one. So the tape did not cause a problem for what 20 years.
I looked, I can see through the radiator with a light all over the surface area.
Do not understand where you are wanting me to ohm out the new sender, please explain more in detail. post to body? body to machine/ground? I take it the post is the nipple the wire is connected to? Old one was screwed in all the way, for over 20 years never touched it, the new one is the same.
"New" just means "never tested in operation". Don't assume it is good just because it is brand-new out of the box.
Is low coolant flow also a possibility.? Stuck temperature regulator maybe.? Your comment "after a couple of minutes the gauge went to RED" appears to support that theory. When the gauge is in the RED have you tried aiming the temp gun directly at the coolant temperature sender.?
Feel the radiator and see if an area is cold and another is hot. If thats the case you can get faulty readings. Have the inside of the radiator cubes cleaned.
Have you had the radiator cap off and could you see flow when it went to red??
I just had the same issue with a JCB JS235HD. Temperature monitor goes critically red within 20 mins to 30 mins. Half pf the rad was cold and half was hot to the touch. Had it flushed, and back up and running, in perfect condition. Been able to work all day without any issues since. Hope that helps.
Is the machine dying when it goes to red?
Yes it will as long as the red danger warning illuminate the dash. Its an immediate warning to shut the engine down to prevent further damage. In other words, it goes into a limp mode.
IMHO you're crediting a 30-year-old machine with far too much in the way of electronic intelligence....... Those E-Series excavators were only one step past being steam-powered.
First item that I would check is the temperature on the outlet side of the engine oil cooler. Another place is on the head behind the thermostat. If those read the same as you have been seeing I would suspect the wiring harness. It's a B model machine manufactured in Japan when there were issues with wiring harness insulation. I've found it less expensive to purchase an automotive temperature gauge with sensor. Put the sensor in and most automotive sensors are twelve volt so run the gauge from a twelve volt battery. Maybe even find a manual gauge with a capillary tube and check it that way. I've looked at plenty of machines from the analog era where the monitor panel noise maker wires were clipped and a set of manual gauges were installed.
Wow! The machine is that old? Well that may be a different kettle-of-fish. But I'll still advise, to have the tubes flushed properly. The best way is to remove the bottom the core.
Watch it I remember when they were new
Lol yes I remember the E's, a friend of mine had one, he used to call me every minute to put back on the tracks. They kept running off. Luckily it was a long stick version, so I was able to just lift them back on using the same machine.
I will aim the temp reader at the sender and report what I find. Thank you. Nige; today Sunday I took reading before I started the engine at 630 PM and one hour later 730 PM. The before starting temperatures were to of radiator 88F; top of hose 85 F; temp sender 75; bottom radiator hose 75F. After one hour temperatures were top of radiator 147F; top hose 126F; temp sender 135F; bottom hose 108F. After one hour the temp gauge in the cab was just over the middle/center of the gauge with the red zone to the right the dial was not close say 1/4 inch from red zone.
Were you working the machine during that hour or was it just sitting idling.? I dunno about anyone else but that sounds like low coolant flow to me. I would not expect the temperature at the sender to be significantly higher than both the temperature of the top hose or the top of the radiator. I would suggest to look at the temperature regulator next.
the engine was only idling. after one hour of idle the temp was top of radiator 147F top hose 126F temp sender 135F It does not make any sense to me, why the temp sender is higher then the hose going to it via the metal elbow, but lower then the top of the radiator. Do you think it its time for a new radiator thermostat? I take it the temp regulator Nige wrote is the radiator thermostat? I can flush the radiator out with it still attached to the machine, but maybe switching out the thermostat first and see what that outcome is, might be the next item to try. thank you for replying, much appreciate every ones suggestions. This site is sooooo useful. The access to so many minds and experienced people.
A lack of flow through the system would explain that. Question is what's causing it. Cat call it a temperature regulator, which is exactly what it is supposed to do; regulate the coolant temperature within a set range once the engine has initially warmed up. See the parts illustration below. I would not suggest to replace the regulator just yet. Remove it and dump it in a pan of boiling water. Does it open.? If it doesn't then replace it and re-test the cooling system performance. If it does then you are in for a radiator removal and internal cleaning. This will involve de-soldering the top & bottom tanks because the radiator is a single unit.
Might want to check the belt on the water pump and how the pump turns
If the belt, fan, thermostat or cowlings are defective, the temperature change would affect the whole radiator system. If the radiator is blocked at the bottom, that area would have a lower temperature since the coolant wouldn't be circulating in that section. If the coolant have not been changed for a long time it would leave some sticky residue mostly at the bottom of the radiator that would result in blocking the inner pores. If you use water rather than coolant. That makes it worst. Water causes corrosion much quicker wether hard or soft. I would have the radiator removed and cleaned properly, you may even have to remove the bottom tank to expose the tubes and use a flat brazing rod and have them cleared. Or maybe replacing the radiator. Been through this same problem a few times. Based on your explanation of your problem i think this your last resort. Greetings to all from Antigua and Barbuda.
Was that one of the engines 'thinking here" that the impeller would turn loose of the shaft or itself where it was epoxied or something like that. Wasnt that a Mitsubishi Id start with a manual gauge, just to rule that out. Then seeing what the top and bottom readings were the flow thru radiator is too slow, allowing it to cool the smaller amount of water that is flowing thru it to have a greater difference in temps. 126f- 108f
Start the engine with the radiator cover off. Allow temp to build to for the thermostat to open if theres circulation visible then the pump is good. If the pump is bad, the coolant or water will just boil and flow from the cover the minute the thermostat opens. I may sound a bit old school. But my methods work on both old and new.
Today August 18 2026, I took out the temp regulator and placed it in 200F water, it did open; did this twice so that's not the problem. Moving on we did a continuity test of the wire from the temperature sender. used a long brown wire from the temp sender wire that is yellow with green strip, that plugs onto the sender, it was not plugged to the temp sender, brown wire back to cab, put one lead of electric tester on the brown wire other electric tester lead was connected to the yellow/green strip wire going into the control box the elect tester zeroed out. This was with the auxiliary power on (not engine running no temp regulator reinstalled yet) and also with the auxiliary power off same result. So the wire from the temp sender the the plug that attaches to the plug end with wires coming out of the dash this is fine. The temp regular is fine. Any further suggestions would be greatly appreciated everyone.
Use a hot plate and put the temp sender in a pan of water hooked up to the system and see what it reads. Or you can use a manual gauge. The monitor panel itself can be the problem. As I recall you can remove the display and dismantle it to check the circuit board.
Have you tried looking for flow in the cooling system as suggested in Post #32 above.?
After trying and still unsuccessful with all other methods, have you yet thought of having the radiator properly cleaned internally?
I’d still prefer your idea of trying to verify coolant flow first. If there were any doubts after that test I would then suggest a sticky beak at the water pump impeller as suggested above by @HATCHEQUIP before going to all the effort of removing and disassembling the radiator.
I picked up the new temperature regulator today and compared the old with the new. See photo below. the new one has a rubber o-ring sealing off the regulator, the old one does not have one and it does not seal one can see through it (12 to 3 on a watch face) in the photo, maybe it wore out over the decades. Both have the pin hole to let air out/escape. That has to part of the problem.
Genuine OEM or aftermarket.? Did the one you removed have a Cat part Number on it.?
It is from the Caterpillar dealer, part number from the parts book for the machine is 9Y33655 the new number is 1265869. The old regulator part number is 9Y3088 with 180F stamped into it, I am looking at it. Note different part numbers. I put the new one in the machine. On the new regulator it has 82C which is 180F. ran the engine at idle for 45 mins the temp did get up to 155F. Increased engine RPM an after 15 mins it only got to 174F. Operated the hydraulics moving arm stick, bucket in the air this did not get coolant 50?50 mix above 174F. The coolant did not get that hot to open the regulator. I ran the radiator the entire time with out the cab. I filed it the brim, at the start the coolant flowded a little bit out of the radiator it was full to the brim. At the end it was about 1 inch down from the brim and I would say it was boubbling AT 174f. At the end the water temp sender unit read 148F The metal elbow above the sender was 171F The top radiator hose was 154F I used a meat thermometer to test the water 50/50 mix in the radiator it read 174. I take it the new regulator never got hot enough to open? I might dig a hole with the machine to see if that gets the temp up. Any suggestions would be greatly appreciated.
1265869 is the listed replacement for 9Y3365, which in turn replaced 9Y3088. So all good there. I would agree. The fact that the radiator got to 174 would indicate that coolant is passing through the bypass line in the cooling system that allows a certain amount of flow through the radiator even when the regulator is completely closed. See the attachment, top of Page 4. You really need to work the machine hard to get the regulator to open fully.
Today Friday, we dug a hole with the excavator through tough hardpan. The machine warmed up a bit for 10 mins first then worked it for ½ hour. I took temp reading before digging; coolant 174F, top radiator 170F, top hose 155F, lower hose 110F, metal elbow sender screws into 180F, temp sender 176F. Temp gauge in dash went into the red zone. I took temp reading after digging the hole; coolant 172F, top radiator 172F, top hose 159F, did not check lower hose, metal elbow sender screws into 180F, temp sender 180 then went down to 168F. Next we tightened the belts, water pump which was a little loose and fan. Next dug another hole. The results were: coolant 172F, top radiator 170F, top hose 147F, metal elbow 175F, temp sender 147F. The temp gauge in the cab was on the line between green and red. This is not normal; the temp gauge should be some distance from the red zone. Do you think the temp gauge in the dash is not reading correctly? Can that happen? The wiring tests are correct; wire off the sender and wire grounded tests. With the water pump belt tension tighten; I was hoping that was the problem but not so. Yes the coolant temp did not get to 180F, but the temp gauge in the dash went to the red zone. Any comments, suggestions? I am stumped.
Looking back I don’t think you ever posted a photo of the gauge in the dash. That would be handy, along with an indication of the needle position when you did the tests above.
Its a possibility that you have two Different sensor readings. One sensor might be reading the actual water temp at the radiator, and the other, a critical engine temperature warning. That why you may be getting a warming light on the dash. It means to shut down immediately.
You dont have to take my word on it, but as an experienced heavy equipment operator for 40 years. Who can repair any equipment i operate, I always got the issues corrected myself in quick time and back to work without having to call a mechanic. I love my job as an operator bro and take seriously with pride.
That's exactly what the machine has. See the snip from the electrical schematic below The signal from the "water temperature unit" (aka coolant temp sender) is what powers the temp gauge on the panel. The "water temperature switch" activates at a set temperature and illuminates a warning light on the dash panel for high coolant temperature. At the same time it sounds a warning buzzer. The specifications for the 8T-9793 normally-closed Switch are as follows. Contacts close at 107.2±2.8°C (225±5°F) with rising temperature. Contacts close at a minimum of 93°C (199.4°F) with falling temperature. As I understand it the OP is concerned about high coolant temp readings on the gauge. I do not recall him ever mentioning anything regarding the high coolant temp warning light/buzzer.
Yes the reason I am looking into this is that the warning buzzer went off while digging a pond the operator does not remember if a warning light came on. I did a ohm test on the new sender it read 300 cold. I am trying to figure out what the two electric wires coming out of the housing right next to the temp sender. Is this the "water temperature switch"? The blue connector is not metric size it is a little loose on the new temp sender. I will get a photo of the water temp gauge in the dash went it is hot.
Correction. That should read “contacts OPEN at 107.2±2.8°C (225±5°F) with rising temperature”
The warning buzzer can go off for a number of reasons, not just high coolant temperature. How can he be sure what it went off for.?
It is. With the key ON unplug the 2-pin connector to the left of the switch and check what happens in the cab in the way of warning lights and/or buzzer. Do you have a manual for this machine and do you know what all the various warning lights are for.?
The connector on single wire sensor looks wrong never saw one like that always a eyelet and a nut
I’ve seen this type before. The connection on the end of the sender looks a bit like a smaller version of the top end of a spark plug.
Have the maintenance and parts manuals
Noticed that when the machine key is turned to auxiliary, not engine started, the water temp gauge moves about 1/4 through the green zone the hydraulic temp gauge does not move. Might be a bad gauge in the dash.
And it appears the yellow wire is cut (to the left of plug)on the 2 wire switch/sensor
No the yellow wire comes out of the back plastic loom it just appears to end (cut off)
Took three photos of the water temp gauge in the dash. one finger in photo is the engine stopped and cold two fingers is the key turned to only auxiliary three fingers is the engine just started I think the problem is the water temp gauge in the dash, the needle for some reason has moved to the right so when engine is up to operating temp it is in the red zone of the in between green red zone.
You could be correct, but your comment below from an earlier post may be relevant and should be investigated further. Reduced conductivity at that terminal due to a "loose connection" could well be affecting the gauge reading.
Well it appears the problem was the water temp gauge in the cab dash. I replaced it, and the needle is not going into the red zone stays in the middle of the green zone. The old one a mechanic noticed was not going to the peg on the left side when engine turned off; was about 3/16 to the right, so when the engine temp was warmed up it would be at the junction of the green and red color area on the dial. All that work just to fine out it was the temp gauge in the dash. Thank you every one for your reply and many suggestions. This forum site is wonderful.
Thanks for the follow-up. This site is truly great, and it's members are very helpful.