Volvo TAMD41 - where is the second Sensor for engine coolant temperature?

Pleinmont

Pleinmont

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Hi
Recently I've been getting the odd intermittent water/coolant temp alarm/flash warnings from the dashboard panel at around 3000rpm but the Temp Gauge (dial) remains as calm and predictable as always (circa 82deg when cruising, 85deg at WOT).
Through process of elimination I think the engine is fine and cooled ok but maybe the alarm/light switch or connector is faulty.

I found the sensor for the Gauge on the thermostat housing (confirmed by unplugging when engine at temp and dial drops to 0) but I cannot find another other one for the alarm/light.
The exploded diagrams online show both of them side by side on the thermostat but mine only has one screwed in with the other hole filled with a blanking plug...

Does anyone know where another coolant or water temp sensor might be located on the engine?
Unless all my alarms/lights and gauge are fed by the one sensor (which seems odd).

Engine is TAMD41P-A from 2005

Thanks IA

1754319433497.png 1754319503994.png
 
Maybe... The oil cooler is plumbed in to the the cooling system so its a possibility.
I'm hoping someone here knows as the internet is drawing a blank...
 
Pleinmont said:
Hi
Recently I've been getting the odd intermittent water/coolant temp alarm/flash warnings from the dashboard panel at around 3000rpm but the Temp Gauge (dial) remains as calm and predictable as always (circa 82deg when cruising, 85deg at WOT).
Through process of elimination I think the engine is fine and cooled ok but maybe the alarm/light switch or connector is faulty.

I found the sensor for the Gauge on the thermostat housing (confirmed by unplugging when engine at temp and dial drops to 0) but I cannot find another other one for the alarm/light.
The exploded diagrams online show both of them side by side on the thermostat but mine only has one screwed in with the other hole filled with a blanking plug...

Does anyone know where another coolant or water temp sensor might be located on the engine?
Unless all my alarms/lights and gauge are fed by the one sensor (which seems odd).

Engine is TAMD41P-A from 2005

Thanks IA

View attachment 197230 View attachment 197231
Click to expand...
This is for the gauge .
The alarm sender is underside of exhaust manifold above oil filter
 
Ah... brilliant. Thanks both.
Also exactly the kind of diagram i was trying to find Plum!

Second question is I assume I would have to drain coolant out before unscrewing and replacing the lower alarm temp sender (and refill afterwards)?
Would you recommend draining all of the coolant out of all the plugs or just a particular section of the engine (near the exhaust manifold)?
 
Pleinmont said:
Ah... brilliant. Thanks both.
Also exactly the kind of diagram i was trying to find Plum!

Second question is I assume I would have to drain coolant out before unscrewing and replacing the lower alarm temp sender (and refill afterwards)?
Would you recommend draining all of the coolant out of all the plugs or just a particular section of the engine (near the exhaust manifold)?
Click to expand...
Don't know but if you have a new sender ready with a smear of Hylomar on the threads, cold engine, pressure cap on (this may help to hold a vacuum and reduce the rate any flows out of hole), remove old one, finger over hole, swap finger for new one. You should only lose a cup full.
 
Plum said:
Don't know but if you have a new sender ready with a smear of Hylomar on the threads, cold engine, pressure cap on (this may help to hold a vacuum and reduce the rate any flows out of hole), remove old one, finger over hole, swap finger for new one. You should only lose a cup full.
Click to expand...
My thoughts exactly.
 
Thanks for the pointers... Yep that sounds pretty straightforward if I can get the threads lined up and not drop anything :unsure::)
A selfie stick helped me finally locate the elusive switch last night under the manifold as you advised (couldn't get my head down that side to see it with my own eyes) (y) Maybe with a bit of serious contortion I can get under there. The connector has been crimped on too, just to add a bit more hassle when trying to swap over to a new one.

In the event that the switch is not faulty and a new one also complains when the revs go over 3000, is there anything obvious that could locally increase the temp of coolant around the exhaust manifold when the coolant in the thermostat area appears to be within the low 80s?
I'm really hoping it's the switch playing up and giving false readings (as the gauge has always looked bang on and still says temp is fine) but just thinking ahead...

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1754471467289.png
 
Hopefully... I thought someone might have given it an extra nip for vibration security as it hangs vertically. I couldn't get it off with my fingers yesterday.
Will try again with pliers (y)
 
Pleinmont said:
Hopefully... I thought someone might have given it an extra nip for vibration security as it hangs vertically. I couldn't get it off with my fingers yesterday.
Will try again with pliers (y)
Click to expand...

Sometimes they will have a little ‘tang’ on the female that goes into a hole on the male spade terminal.

Should come off with some wiggling.

This solves the mystery for me as well..
 
jakew009 said:
Sometimes they will have a little ‘tang’ on the female that goes into a hole on the male spade terminal.

Should come off with some wiggling.

This solves the mystery for me as well..
Click to expand...
No worries, took a while but got there in the end 😆
That's a good point re the tang and hole👍
 
Happy to report that the VP temp sensor on the manifold has been replaced with a new one and the overheat beeper has not gone off once during 3 days of boating (including a couple mins of WOT now and again).
Looks like it was on the fritz and the engine coolant temp dial was in fact correct all along. For once, a low cost repair 🙌 :)
Had a few sleepless nights worrying about it being a much bigger problem that might have needed a teardown but all is well with the engine 🙏
 
Pleinmont said:
Happy to report that the VP temp sensor on the manifold has been replaced with a new one and the overheat beeper has not gone off once during 3 days of boating (including a couple mins of WOT now and again).
Looks like it was on the fritz and the engine coolant temp dial was in fact correct all along. For once, a low cost repair 🙌 :)
Had a few sleepless nights worrying about it being a much bigger problem that might have needed a teardown but all is well with the engine 🙏
Click to expand...
excellent news, well done, thanks for letting us know. It is in a very inaccessible position, did you manage without draining the coolant or even without removing the main heat exchanger?
 
Ah I folded at the DIY option when I realised just how horrible the location was to get a spanner in...
I willingly paid for our local Volvo legend/guru Bob to do the honours 🙏 🙌

I don't think the exchanger came off (will know for sure when i see the labour charge!) so think he just lost a bit of coolant during the swap over. There was a litre or so in the bilge....
If he managed to do it without the exchanger coming off he must be some kind of contortionist.

Very pleased it's done and sorted - can reward myself with a heading sensor for the radar overlay now it seems the engine is ok ;)
 
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