• Thank you for visiting HeavyEquipmentForums.com! Our objective is to provide industry professionals a place to gather to exchange questions, answers and ideas. We welcome you to register using the "Register" icon at the top of the page. We'd appreciate any help you can offer in spreading the word of our new site. The more members that join, the bigger resource for all to enjoy. Thank you!

Bobcat 331 Temperature / Coolant Alarm Gremlin

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
Hi all.

I picked up an old Bobcat 331 last fall. It was neglected by its previous owner(s). I've gotten most of the bugs worked out of it and it's been earning its keep for the most part. However, there's one issue that I haven't figured out, yet. Once it gets up to working temperature, the coolant light comes on and the buzzer goes off.

Here's what I know:

The cooling system is full of new coolant.
The water pump is circulating coolant.
Using a laser thermometer, the oil pan is at about 185-186 degrees F.
The thermostat housing where the temp sensor is, is at 150 degrees F. (so is the radiator)

Yet the coolant light comes on and the buzzer is complaining.

Voltage at the battery (terminal to terminal) is 12.86v. Same reading from the positive terminal to the frame.
With the ignition key in the "on" position, the wire that attaches to the temp sensor is showing 11.75 volts.
With the ignition key in the "off" position, that same wire shows about 300mv. The wires at the the back of the instrument cluster also show about 300mv when the ignition is off.
Sometimes the the temperature gauge will drop to all the way to the left (zero), with the buzzer still sounding. (I don't know how to interpret that symptom).

Questions:

1. Shouldn't voltage be at 0mv with the ignition off?

2. Would moisture in the ignition switch or somewhere else cause this? (There is some condensation inside the gauge assembly).

Does anyone have a service manual or electrical diagram they could share? Has anyone had this issue before?

Any help pointing me in the right direction would be greatly appreciated.

Thanks
 

John Canfield

Senior Member
Joined
Apr 27, 2009
Messages
431
Location
Texas
Occupation
Ranching
Check out Andrew Camarata’s YouTube channel, I’m almost positive I watched a video of his where he had a similar problem on maybe a Yanmar mini-ex, this might give you some troubleshooting ideas. He runs a bunch of old equipment and does his own repairs.
 

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
Serial #? This is not an uncommon problem with the 300's, usually the panel itself unfortunately. Did you actually unplug each connector from the panel and check for moisture? If there is moisture under the gauges more than likely the panel has been compromised and you will find moisture in the connections. Be careful unplugging them because sometimes the pins are corroded and will break off.
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
John, thanks for that! I found his video where he diagnosed that same problem on his Yanmar. (He's a very knowledgeable guy, btw.) I got my hands on a service manual, but it doesn't cover the serial number on my machine. However, it's pretty close to what I have. The one difference that i found so far, is that my machine has a relay that's not shown on the wiring diagram.
20190621-134204.jpg


I ran the machine until the buzzer and temp light came on. Unplugging the relay turned off them both off. Something is activating the relay, but the electrical diagram that I have doesn't show what the relay is tied to. The purple and white wire runs in parallel with the engine temperature switch. If it gets grounded, the temp light and alarm both come on. The orange wires appear to go to the ignition switch? And the black wire?

Anybody familiar with this? I don't know why this relay is even needed. The only function that it seems to perform is to turn on the light and the buzzer independently of the engine temperature switch.
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
Bswwood, I didn't unplug the gauges. I'm going to dig into it a little more tomorrow and try to trace where that black wire leads to. Did they add a temp sensor to the hydraulic circuit?

Serial number is 00x0x_jDt0XIuvIdK_600x450.jpg
 

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
John, thanks for that! I found his video where he diagnosed that same problem on his Yanmar. (He's a very knowledgeable guy, btw.) I got my hands on a service manual, but it doesn't cover the serial number on my machine. However, it's pretty close to what I have. The one difference that i found so far, is that my machine has a relay that's not shown on the wiring diagram.
20190621-134204.jpg


I ran the machine until the buzzer and temp light came on. Unplugging the relay turned off them both off. Something is activating the relay, but the electrical diagram that I have doesn't show what the relay is tied to. The purple and white wire runs in parallel with the engine temperature switch. If it gets grounded, the temp light and alarm both come on. The orange wires appear to go to the ignition switch? And the black wire?

Anybody familiar with this? I don't know why this relay is even needed. The only function that it seems to perform is to turn on the light and the buzzer independently of the engine temperature switch.
That's a timer relay, Did all gauges go out when unplugged?
 

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
That's a timer relay, Did all gauges go out when unplugged?
The timer only controls how long the buzzer will run according to the manual. Black is ground, orange goes to buzzer and is tied into guages, same with purple thru a series of diodes
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
20190621-211122.jpg
I didn't think to check the other gauges. I was paying attention to the temperature light and the buzzer.

QrvNkyR


If that's the timer, then it's on the wiring diagram. Seems to be set to kick on after about 20 minutes
 
Last edited:

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
Ignore what I said about the panel now that I have the serial number. I don't see a hydraulic temp sensor for your machine. I don't see anything in service manual that will help trouble shoot this issue. I would replace the sender 6664895, also check the diodes for current flow in one direction, the diodes are tied into the gauges and buzzer circuit.
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
The timer only controls how long the buzzer will run according to the manual. Black is ground, orange goes to buzzer and is tied into guages, same with purple thru a series of diodes

Dumb question, what is the purpose of this timer? Is it just to light up the gauge panel and make noise when the ignition is first turned on?
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
Ignore what I said about the panel now that I have the serial number. I don't see a hydraulic temp sensor for your machine. I don't see anything in service manual that will help trouble shoot this issue. I would replace the sender 6664895, also check the diodes for current flow in one direction, the diodes are tied into the gauges and buzzer circuit.

I think that the relay is the path that's giving the ground contact to the temp light and buzzer. If the temperature switch was bad, unplugging the relay shouldn't silence the alarm. Should it?
 

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
Diodes in right console, and not a dumb question at all, but yes I think that is all it is used for. Manual does not go in depth
 

Attachments

  • 15611674789122917590420223570736.jpg
    15611674789122917590420223570736.jpg
    1.6 MB · Views: 11

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
O
I think that the relay is the path that's giving the ground contact to the temp light and buzzer. If the temperature switch was bad, unplugging the relay shouldn't silence the alarm. Should it?
One way to find out, unhook the water temp sender when the machines at operating temperature and see if the buzzer in light goes off, and if you touch that wire to ground the buzzer and light should come on. It looks to me like the temp light itself is independent of the timer relay
 

joispoi

Senior Member
Joined
Mar 1, 2008
Messages
1,284
Location
Connecticut
O

One way to find out, unhook the water temp sender when the machines at operating temperature and see if the buzzer in light goes off, and if you touch that wire to ground the buzzer and light should come on. It looks to me like the temp light itself is independent of the timer relay

Unhooking the sender didn't silence the alarm. On the diagram, the temp light and timer ground paths + the buzzer connect at the node just above the water temp switch. It looks like either the sender or the timer can provide ground to both the light and the buzzer. I suspect that the relay is bad. If it's a $50 relay that only makes noise before startup, I think that the fix might just be to unplug the relay.
 

Bswwood

Active Member
Joined
Jun 19, 2019
Messages
41
Location
Utah
It's possible the thing I find interesting is it has to get to working temperature before it goes off, this seems to be the puzzling part
 

PNW_Newbie

Member
Joined
Oct 28, 2022
Messages
14
Location
Port Angeles WA
I wish this thread had finished and an answer to his problem was posted...I am a total newbie and my 331 just started doing the same exact thing...First hurdle for me is getting the plastic handle unscrewed from the rod that controls the blade so I can take the right console cover off...Half can of PB blaster down and three days of soaking with no luck...sigh..lol
 
Top