Volvo temp gauge over reading?

[Flybrain]

I had my boat out of the water for a service.

I had the o-ring replaced on my heat exchanger as well.

When I launched the boat the gauge showed it was heating to over 100 degrees celsius.

I have since changed the thermostats, and tried bleeding the coolant twice.

The raw water side seems to be working well. With an IR thermometer the exhaust elbow and impeller housing were reading a maximum of 16 degrees celsius.

I thought the heat exchanger might be blocked so have taken that off (it was clean). The rubber seals were maybe not seated very well so the water wasn’t passing through the heat exchanger properly? I will refit it tomorrow.

The overheat alarm hasn’t sounded (I will test it works tomorrow).

Is it possible the gauge is over reading? Bad earth?

Any suggestions welcome! Thanks in advance

 

[vas]

can you identify the volvo sender on the engine block? Usually close to the thermostat housing. Aim your IR meter there for starters.
Slightly confused as exhaust elbow measuring 16C with engine running is imho almost impossible even after the mixer... I mean even hitting the exhaust hose should show more than that with engine running for a few mins!
Did the gauge show a normal value when stone cold (like 15-20C) and then went up to 100C within a few mins of firing up or as soon as you turned the switch? Former, v.odd (sender/gauge issue), latter sometype of short.
Volvo senders have all their info/data online so once you identify the model (99% need removing sender off and scraping paint off the hex next to the threads) so you could check the sender with a ammeter.
I'd start with checking cabling that may have been disrupted with your servicing work.

Guess you would get more detailed feedback if you gave engine make and model.

V.

 

[Flybrain]

Thanks for your reply. It’s a Volvo AD31P.

The gauge showed a normal stone good value and it took a long time to go up to about 80, once under load and at only about 2000rpm it showed it being over 100.

I will go and check the cabling now and remover the sender. I’ll also check the exhaust elbow reading with the IR thermometer (and the thermostat housing)

Thanks again

 

[Portofino]

Airlock ? Is there a way of burping it …both sides btw ? Are you sure the closed coolant sides ok ? Filled up burped ?

Check the water pump side the circulation.Was any of this disturbed .New pipes fitted or old replaced ?check them inside incase the pulling / tugging delaminated them ? .
Even a rusty internal elbow will restrict flow when it’s needed at higher rpms

Those IR readings are low if accurate .

Do one of the block and around the cylinder head as well as the other two .

If it’s a twin swop gauges around and make a long jumper ( wire with spades ) to swap connections for the senders from one gauge to another in situ assuming you can easily unplug them ?? Saves phaffing dismantling the dash , and tests the senders out as well a gauges .

 

[vas]

not at all familiar with that engine, but decent temp on the gauge when cold, decent slow rise to 80 and then when pressed shoots to 100 doesn't look like anything to do with a gauge/sender issue!
Check what Porto above states, that coolant is fine, impeller is not foobared, no excessive growth on hull/prop (probably irrelevant if the boat was out I expect it was cleared/antifouled as well?)
And make sure your IR meter works right (or no offence know how to use it!) there's no way running engine exhaust elbow shows 16C...

V.

 

[Flybrain]

Hi just back from a sea trial.

Thanks for the suggestions.

It was a bad earth to the back of the temperature gauge. I’ve got no idea how that had happened!

 

[snowbird30ds]

there's no way running engine exhaust elbow shows 16C...

That can happen if the surface aimed at is shiny, best for any sort of shiny surface with IR thermometers is to apply some matt black tape before checking for a good reading, even a bit of masking tape and a permanent marker will do.

 

[vas]

That can happen if the surface aimed at is shiny, best for any sort of shiny surface with IR thermometers is to apply some matt black tape before checking for a good reading, even a bit of masking tape and a permanent marker will do.

correct!
I've had to do the black permanent marker thing on various pipes at home CH when I was debuging an intermittent fault of a gas boiler.
tbh, I was expecting the engine to have a cast iron painted elbow though, probably not the case.