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802a Coolant Fault Light

C

Clorox

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I just purchased a used MEP-802a and am getting a coolant high temp fault light after four hours or so of use. At that point the generator shuts itself off.

Currently the unit is being used to power a house since we will most likely not have power restored for another week. High loads such as the water heater, microwave, etc have been turned off and the generator is being run at 25-60% utilization according to the gauge on the generator.

When I picked the unit up, the coolant was a little low so I did add about 12 oz to the catch can to bring it up to the cold line. The gauge for the coolant temp on the front is showing around 220 degrees when it shuts down. Overall the generator is running fine aside from the coolant issue, fuel burn looks to be around the stated .5 gallon/hour.

In reviewing the -24 TM, I see it suggests thermostat and water pump for items to check. Is there anything else I should check? I don't have an infrared thermometer to verify things with at the moment. Any suggestions on other things I could check? Is the thermostat something that I could get at NAPA?
 
C

Clorox

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Ok, I have an update. I fired the generator back up this morning after sitting all last night. Current temperature is 33 degrees and it was down around 20 degrees over night. The generator ran for 10, maybe 15 minutes and shutdown with the high coolant temp fault light on. The catch can has coolant between the cold and hot lines, nothing feels super hot. I am wondering now if it might be the sensor? That would be like a 200 degree change in coolant temperature in 10 minutes while at 30-50% utilization. That just seems a bit of a stretch but I am not a mechanic either.
 
T

Toolslinger

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Good morning, and welcome aboard...

The experts will be along shortly. Good that you have already gone through the -24.

Of note, the temp gauge is a separate circuit circuit from the high temp light, so one can go bad, but you still have the other either as reference, or safety.
I don't recall what the normal run temp is. I'd agree it seems like the temp rise seems pretty quick compared to your ambient temp.
 
C

Clorox

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Thanks Toolslinger! I am still going through the TMs to see if I can track anything else down that might help.

My guess is that 180-200 would be the normal operating window.
 
C

Clorox

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I have done a little more troubleshooting, daylight is a nice thing to have.

I started the generator up and flipped the battle short switch. Then I shut most of the load in the house off and closed the circuit breaker. Generator is running about 25% utilization. A few minutes later the coolant temp light comes back on. The gauge is showing around 200 degrees. I ran the generator like this for 15-20 minutes. The upper radiator hose is nice and warm, probably around 120 degrees. The lower hose is cool, around the same temperature as inside the cabinet. The coolant temperature gauge is staying around 200 degrees.

From my non mechanic point of view, I would say that the thermostat is working correctly along with the water pump. My guess is now that the sensor that the fault light is using is the culprit. I am going to keep running it in the mode a little longer and keep an eye on it.
 
R

Ray70

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I believe you are correct. The engine normally runs at about 200F ( according to the gage ) which in reality is about 180F
The shut down in controlled by the 2 pin thermal switch located on the oil filter side of the engine, near the thermostat.
You could remove it and attach a DMM, heat it up in a pot of water and see at what temp the resistance changes drastically ( not sure if it's NO or NC, but it will be readily obvious once you probe with a meter.
 
C

Clorox

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Thanks Ray, I will give that shot when the power is back on. I have been running the unit for a few hours this afternoon and the temp gauge is around 200-220. The fault light is on but I have it in battle short mode. I am 99% sure that the temp sensor is the problem. In looking at the TM I am trying to find a part number so I can order a replacement. Does anyone know if there is a cross reference that would be available at a local parts store?
 
Guyfang

Guyfang

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Gents, before we get all hot and bothered:

3. Cooling System:
Type Pressurized radiator and pump
Capacity 8.2 qts. (7.8 L)
Normal Operating Temperature 170-200 °F (77-93 °C)
Temperature Indicating System
Voltage Rating 24 VDC

So, if the sending unit is sending the right temp, (220) to the Meter AND Fault Indicator, then the sender is in fact right. Were it me, I would test the sending unit AND meter, then KNOW if the sender is bad. If I was in a hurry, I would do as you are. Buy a sending unit. But that is not trouble shooting.
 
R

Ray70

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Ah Ha! seems I mis-read slightly. I thought you were tripping the over temp light with the gage reading at 200* , but in fact you said temp increased by 200* above the ambient temp. to 220.
So perhaps you really are overheating? Which could be a stuck closed thermostat, or a thermostat installed backwards.
As Guy stated, best to test everything. First you need to determine what the actual engine temp is.
If the engine feels hot but the upper hose and radiator are still cold I'd suspect the thermostat.
An IR thermometer will tell you pretty quickly.
 
FarmingSmallKubota

FarmingSmallKubota

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Take a picture of your gauge, several have put aftermarket gauges in that are not accurate. close but not close enough. Since you do not have a temp gauge this might be a clue
 
Guyfang

Guyfang

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A coolant high temperature switch in conjunction with the fault system provides automatic shutdown in the event
that coolant temperature exceeds 225±5 °F (104±3 °C). The COOLANT TEMP indicator indicates the engine
coolant temperature from 120 to 240 °F (48 to 115 °C).

TESTING The Temp meter:
1. Shutdown generator set.
2. Open left side engine access door and disconnect negative battery cable.
3. Release control panel by turning two fasteners and lower control panel slowly.
4. Isolate generator set VOLTAGE adjust potentiometer (WP 0036, Figure 1, Item 47) by disconnecting wire
156A at terminal 1 and wire 157B at terminal 2 from AC voltage regulator (WP 0020, Figure 1, Item 21).
5. Set multimeter for ohms and connect between terminals L and R of generator set VOLTAGE adjust potentiometer
(WP 0036, Figure 1, Item 47).
6. Adjust VOLTAGE adjust potentiometer (WP 0036, Figure 1, Item 47) until multimeter indicates 117 to 143
ohms resistance.
7. Remove multimeter, but do not disturb potentiometer adjustment.
8. Disconnect and isolate electrical lead from terminal S of COOLANT TEMP indicator (WP 0036, Figure 1,
Item 1 8).
9. Connect jumper wire between disconnected wire 156A and terminal S of COOLANT TEMP indicator (WP
0036, Figure 1, Item 18).
10. Connect jumper wire between disconnected wire 157B and terminal G of COOLANT TEMP indicator (WP
0036, Figure 1, Item 18).
11. Connect negative battery cable and move generator set MASTER SWITCH (WP 0036, Figure 1, Item 42) to
PRIME & RUN position.
12. COOLANT TEMP indicator (WP 0036, Figure 1, Item 18) should indicate between 116 and 164 °F (47 and
73 °C).
13. Move MASTER SWITCH (WP 0036, Figure 1, Item 42) to OFF position and disconnect negative battery
cable.
14. Repeat Steps 5 through 7 above, setting potentiometer between 58.5 and 71.5 ohms.
15. Connect negative battery cable and move MASTER SWITCH (WP 0036, Figure 1, Item 42) to PRIME &
RUN position.
16. COOLANT TEMP indicator (WP 0036, Figure 1, Item 18) should indicate between 156 and 204 °F (69 and
96 °C).
17. Move MASTER SWITCH (WP 0036, Figure 1, Item 42) to OFF position and disconnect negative battery
cable.
18. Replace COOLANT TEMP indicator (WP 0036, Figure 1, Item 18) if indications are other than above.
19. Remove jumper wires and connect electrical leads to COOLANT TEMP indicator (WP 0036, Figure 1, Item
18) and AC voltage regulator (WP 0020, Figure 1, Item 21).
20. Raise and secure control panel.
21. Connect negative battery cable and close left side engine access door
 
Last edited:
Guyfang

Guyfang

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Testing the High Temp switch:

1. Remove coolant high temperature switch (WP 0092, Figure 1, Item 5) (Removal).
2. Suspend coolant high temperature switch (WP 0092, Figure 1, Item 5) in a container of 50/50 mixture of
antifreeze and water so that sensing element is completely immersed but not touching sides or bottom of
container.
3. Suspend a reliable thermometer in container. Do not allow end of thermometer to rest on bottom of container.
4. Set multimeter for ohms and connect between coolant high temperature switch (WP 0092, Figure 1, Item 5)
terminals. Multimeter should indicate open circuit.
5. Gradually heat antifreeze/water mixture, stirring so that heat will be evenly distributed and observe thermometer
and multimeter.
6. At between 220 and 230 °F (105 and 110 °C), multimeter should indicate continuity.
7. Replace coolant high temperature switch (WP 0092, Figure 1, Item 5) if it fails to operate as above.
8. If replacement is not needed, install coolant high temperature switch (WP 0092, Figure 1, Item 5) (Installation
 
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