Volvo MD22L Erratic temperature gauge problem
- Thread starter Rich Stidger
- Start date
I humbly award @Ralph Johnstone the esteemed title of Wizard Extraordinaire.
His diagnosis of a bad ground at the gauge is undoubtedly my failure mode. Today at home I think I have proved his solution.
I took a known good fuel gauge and an oil pressure sender and hooked them up with a 12V power source. 12V power and ground to the gauge, ground to the sender, and the sender to the gauge. The gauge and the sender work just like the temperature gauge and temp sender that are on my boat. So with the oil pressure sender at zero pressure it has 240 ohms (like the temperature sender at room temperature) to the gauge and the gauge reads LOW.
Now removing the ground reference on the gauge the gauge now reads HI (pegged). This is exactly the failure that I see on my boat. Since all of my gauges in the engine panel share a common ground, and the temperature gauge is the only one that reads faulty, then I believe that the fault is at the ground of just the temperature gauge.
When I get back on board I will pull the panel and find the bad ground.
I am embarrassed to admit that I have been chasing this intermittent fault for at least 3 years, but I think I have it solved now.
I will post confirmation of the repaired fault next week. Thanks to all who contributed.
His diagnosis of a bad ground at the gauge is undoubtedly my failure mode. Today at home I think I have proved his solution.
I took a known good fuel gauge and an oil pressure sender and hooked them up with a 12V power source. 12V power and ground to the gauge, ground to the sender, and the sender to the gauge. The gauge and the sender work just like the temperature gauge and temp sender that are on my boat. So with the oil pressure sender at zero pressure it has 240 ohms (like the temperature sender at room temperature) to the gauge and the gauge reads LOW.
Now removing the ground reference on the gauge the gauge now reads HI (pegged). This is exactly the failure that I see on my boat. Since all of my gauges in the engine panel share a common ground, and the temperature gauge is the only one that reads faulty, then I believe that the fault is at the ground of just the temperature gauge.
When I get back on board I will pull the panel and find the bad ground.
I am embarrassed to admit that I have been chasing this intermittent fault for at least 3 years, but I think I have it solved now.
I will post confirmation of the repaired fault next week. Thanks to all who contributed.
Wow ! Can't wait for that to arrive in the mail. Makes up for this morning when I got bitten when breaking up a squabble between our rabbit and parrot.
I’ve had a couple situations like this. One one a cheap temp sending unit that increased resistance with heat causing the gauge to slowly and faulsely creep up. The second is on my wakeboard boat. The more is a large ge connector and the temp pin is bad. The temp will increase ( move up) with increasing power loads ( blower, stereo) lights. I think the second also involves a bad ground somewhere. I’d run a home run wire from the sender to the gauge and see what happens.
OK, update. Unfortunately, as I began to T/S, the problem was not present and the gauge was reading normally.
I pulled the Volvo panel and removed the connector and the gauge. There was light corrosion on the male and female spade connectors. I cleaned up the male connectors with a fiberglass pencil tool and I soaked the female spade connectors in vinegar before brushing with the fiberglass pencil as best I could. I pinched the female shoulders of the spade connector too. I sprayed all connections with DeOxit cleaner and reassembled. BTW, I cleaned all of the connectors for all three gauges at this time.
Upon startup, the temp gauge looked good- reading normally. The next day after 30 minutes of running the temperature gauge went erratic again. From normal 185F to 250F to 200F and back to normal. It did this repeatedly.
So obviously the problem was not fixed.
I am now thinking that the problem may be inside of the gauge. I still think it is a grounding problem. The ground for the temp gauge is in a string connection with the other two gauges and the tach. All other gauges are reading properly with no erratic movements. This suggests that the ground failure is at or inside of the gauge. The ground is also connected to a circuit board whose function is unknown.
Lastly, on a 2.5 hour run this afternoon the temp gauge performed normally. No erratic movements at all.
So it looks like my following action choices are:
1- Live with the problem. Believe the gauge when it is not jumping around and ignore it when it goes berserk.
2- Replace the gauge and see if the problem returns. A Volvo gauge is $100 but I could swap in a generic temp gauge for under $20.
I hate intermittent problems. I need to visually see the problem or measure the symptom and then after doing a repair be able to observe or measure that the problem is gone. If I can't do that, then my confidence that I have fixed the problem is low.
Here are some before and after cleaning photos of the spade connectors. BTW, there are diamond blade cleaners that are supposed to be good for female spade connectors. I have some on order for the next malfunction......
I pulled the Volvo panel and removed the connector and the gauge. There was light corrosion on the male and female spade connectors. I cleaned up the male connectors with a fiberglass pencil tool and I soaked the female spade connectors in vinegar before brushing with the fiberglass pencil as best I could. I pinched the female shoulders of the spade connector too. I sprayed all connections with DeOxit cleaner and reassembled. BTW, I cleaned all of the connectors for all three gauges at this time.
Upon startup, the temp gauge looked good- reading normally. The next day after 30 minutes of running the temperature gauge went erratic again. From normal 185F to 250F to 200F and back to normal. It did this repeatedly.
So obviously the problem was not fixed.
I am now thinking that the problem may be inside of the gauge. I still think it is a grounding problem. The ground for the temp gauge is in a string connection with the other two gauges and the tach. All other gauges are reading properly with no erratic movements. This suggests that the ground failure is at or inside of the gauge. The ground is also connected to a circuit board whose function is unknown.
Lastly, on a 2.5 hour run this afternoon the temp gauge performed normally. No erratic movements at all.
So it looks like my following action choices are:
1- Live with the problem. Believe the gauge when it is not jumping around and ignore it when it goes berserk.
2- Replace the gauge and see if the problem returns. A Volvo gauge is $100 but I could swap in a generic temp gauge for under $20.
I hate intermittent problems. I need to visually see the problem or measure the symptom and then after doing a repair be able to observe or measure that the problem is gone. If I can't do that, then my confidence that I have fixed the problem is low.
Here are some before and after cleaning photos of the spade connectors. BTW, there are diamond blade cleaners that are supposed to be good for female spade connectors. I have some on order for the next malfunction......
All of the connectors are clean. I measured zero ohms across all of the ground pins on the gauges with all connectors installed. The ground connection to the temp gauge seems to be solid.Guessing does work.
Jim...
I'm still leaning toward an intermittent gauge with possibly a faulty ground wire INSIDE the gauge.
However, short of replacing the gauge, I can't think of any way to prove that the gauge is intermittent. Tapping on the gauge itself doesn't produce the bad reading.