Engine Temp Fluctuating

[oceaneyes]

I noticed today that my engine temperature starting fluctuating abnormally. Last season the boat ran at 185 almost all the time, never over. This season the engine temp will read 136, 175, 164, and will just jump around. Could this be a bad thermostat or sensor?

 

[Harry]

Temp sensor, almost 100% certain.

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[oceaneyes]

Makes sense to me. Do you have a part number or link?

 

[Harry]

What motor do you have? I'm a D6. I can give you a number for D6 when I get home tomorrow.

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[oceaneyes]

D4 260

 

[BB marine]

Water / Coolant temperature sensor #1624368. Replacing the sensor is probably the right diagnosis if guessing. I would still recommend checking the actual operating temperature of the engine to confirm it is not a open or stuck thermostat. If you are operating the engine in cooler water the fluctuation of temperature readings would be more. If in operable thermostat is the case. A quick sea trial with a temp gun will tell the story. Run the engine up to full load and operate at 50% load or higher for a few minutes check the operating temperature with the gun and compare it to the Volvo EVC display.

 

[oceaneyes]

Hi Brian,

Silly question - what am I shooting with the temp gun? I'm more familiar with gas engines and these look a little different to me.

Thank you!

 

[BB marine]

The Block. You want to be checking the block temperature. If the block temperature maintains an even temperature of between 175F to 185F and the EVC is showing temperatures 136, 175 , 165 continuously then I would say the sensor is bad because the thermostat is a 176 to 200 F. If you shoot the block and see a a steady temperature of 150 to 175 and no higher I would say the thermostat is bad.

The blocks temperature will remain somewhat constant because it is the heat source. The coolant will fluctuate more until the Thermostat has stabilized it. If the Thermostat is bad you may see a cooler engine temperature and more flexuation of temperature. Remember the EVC is a programed reading it will not always show 1 F increments. It may show 5F or 10F increments. Once again I would guess it is a sensor but I would want to prove it.

 

[oceaneyes]

Thank you!

 

[doke01]

The wire to the temp sensor could also be an issue. Mine has some corrosion on it and did the same thing. Just required cleaning of the connector.

 

[oceaneyes]

I noticed my coolant cap is hissing and I’ve always lost a little bit of coolant near the hot water heater on the starboard side. This is on my list as well but haven’t gotten to it yet. I’m going to look for leaks on the seawater side.. that’s what I’ve been reading.

Could it be related?

 

[oceaneyes]

The wire to the temp sensor could also be an issue. Mine has some corrosion on it and did the same thing. Just required cleaning of the connector.

Disconnected the harness, cleaned, sprayed with CRC, reconnected and it’s holding a consistent 185 now. Hopefully this lasts at least now I know where the sensor is located. Off to solve the coolant issue.

 

[Eric R]

The wire to the temp sensor could also be an issue. Mine has some corrosion on it and did the same thing. Just required cleaning of the connector.

Disconnected the harness, cleaned, sprayed with CRC, reconnected and it’s holding a consistent 185 now. Hopefully this lasts at least now I know where the sensor is located. Off to solve the coolant issue.

I’m going to be checking mine now! I also noticed this fluctuation starting on my D4-260 as well. Did an 8 hour cruise the other day and most of the time it was locked at 185 like it always has, but then out of nowhere I’d see it blip to like 135, 150, 95, and then settle down again. Sounds like it’s most like the same issue for me. Where is this sensor located? Haven’t looked it up yet.

As for the coolant at the water heater, I also had this exact same issue. It was a simple fix. The threads on the fitting that connects the hoses just needed some resealing. I did mine during a coolant flush when it was empty so I didn’t have to worry much about loss, but you should probably at least clamp the hoses to avoid much spill and getting air into things.




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[oceaneyes]

The wire to the temp sensor could also be an issue. Mine has some corrosion on it and did the same thing. Just required cleaning of the connector.

Disconnected the harness, cleaned, sprayed with CRC, reconnected and it’s holding a consistent 185 now. Hopefully this lasts at least now I know where the sensor is located. Off to solve the coolant issue.

I’m going to be checking mine now! I also noticed this fluctuation starting on my D4-260 as well. Did an 8 hour cruise the other day and most of the time it was locked at 185 like it always has, but then out of nowhere I’d see it blip to like 135, 150, 95, and then settle down again. Sounds like it’s most like the same issue for me. Where is this sensor located? Haven’t looked it up yet.

As for the coolant at the water heater, I also had this exact same issue. It was a simple fix. The threads on the fitting that connects the hoses just needed some resealing. I did mine during a coolant flush when it was empty so I didn’t have to worry much about loss, but you should probably at least clamp the hoses to avoid much spill and getting air into things.




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Thanks for the info about the coolant. I’ll take a couple pics of the temp sensor soon. It’s still half apart.

 

[oceaneyes]

The wire to the temp sensor could also be an issue. Mine has some corrosion on it and did the same thing. Just required cleaning of the connector.

Disconnected the harness, cleaned, sprayed with CRC, reconnected and it’s holding a consistent 185 now. Hopefully this lasts at least now I know where the sensor is located. Off to solve the coolant issue.

I’m going to be checking mine now! I also noticed this fluctuation starting on my D4-260 as well. Did an 8 hour cruise the other day and most of the time it was locked at 185 like it always has, but then out of nowhere I’d see it blip to like 135, 150, 95, and then settle down again. Sounds like it’s most like the same issue for me. Where is this sensor located? Haven’t looked it up yet.

As for the coolant at the water heater, I also had this exact same issue. It was a simple fix. The threads on the fitting that connects the hoses just needed some resealing. I did mine during a coolant flush when it was empty so I didn’t have to worry much about loss, but you should probably at least clamp the hoses to avoid much spill and getting air into things.

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Hi Eric - Below are three photos showing you the temp sensor. It's a little tight but if you remove the two bolts you can get enough access to clean the connector and replace. I think we'd have to take more apart to replace the entire sensor.

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gallery2.php?g2_itemId=79534
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