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Old 23-07-2010, 14:00   #1
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Volvo MD22 - errr, Where's the Thermostat ? :-)

Not mine - on me Father's Motorboat.

Had a brief look last weekend, snap below:-




Online I have this:-



Volvo Penta Exploded view Thermostat housing MD22A, MD22L-A, TMD22A - MarinePartsEurope.com

First question is:

1) where da fook is the thermostat on the engine couldn't work it out last weekend Thinking it is front r/h side top? (just past the MD22 in the photo) - as this is where the water temperature sender is (I think it's item 9 in the schematic).......but can't say that around about looked like it contained a thermostat

2) anyone have an idea why both engines would not be showing any water temperature on the guages? The other guages reading ok and engines sound fine and not over hot..............Put a tester on both the wiring from engine to guages and then seperately through the temperature sender itself and power getting through. The Guages do flick a millimetre when ignition on (so needles not stuck!).........initial thinking was that thermostats were stuck open so engines simply not getting hot - but had a run around the bay recently and still nothing at all Boat not had much use in recent years, but engines started up every few months or so (BTW they are 13 years old - still look factory fresh, despite having in the past had plenty of use - me father has an aversion to dust in the engine bay, let alone oil ). Possible that both temperature senders have decided to give up at the same time?..............or are we missing something obvious? (plan was to look at the thermostats - if we can find them and not buried under anything else).
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Old 23-07-2010, 14:27   #2
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Just re-read the schematic...........(the link has a key)

no. 6 is a "Thermo monitor"...........errr, what's that do?
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Old 23-07-2010, 14:34   #3
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Quote:
Originally Posted by David_Old_Jersey View Post
Just re-read the schematic...........(the link has a key)

no. 6 is a "Thermo monitor"...........errr, what's that do?

That is the temp sending unit.

9 looks like a temp switch. High temp alarm.
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Old 23-07-2010, 15:17   #4
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You're looking in the right place.
As Surya says, 6 is the temp. sender.
See page 98, Workshop Manual ➥ http://www.nathape.com/res/Logoundan...ginerepair.pdf
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Old 23-07-2010, 15:21   #5
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That is the temp sending unit.

9 looks like a temp switch. High temp alarm.
High temp alarm? makes sense and good it hasn't gone off. unless it's also stopped working

What's really annoying is that the schematic looks exactly like I would expect - I just couldn't see anything on the engine that looked like it! well - not where I was looking (my excuse is not familiar with the engine - father's excuse is that never had any problem for 13 years ).

Will have another looksee at the weekend.
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Old 23-07-2010, 15:43   #6
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You're looking in the right place.
As Surya says, 6 is the temp. sender.
See page 98, Workshop Manual ➥ http://www.nathape.com/res/Logoundan...ginerepair.pdf
Cheers for that Gord - P16 - wanna play spot the thermostat

My guess is at the front of the engine (not shown on P16) and against the bulkhead - which may explain why not spotted by me............
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Old 23-07-2010, 16:26   #7
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I really doubt that both thermostats or temp. senders would go bad at the same time. Possible, but not likely. Is there anything in common on the instrument panel connecting the two gauges? If you can find out what the full scale deflection voltage is and then feed some voltage to the gauges, do they work? Its a lot easier to check them than it is to pull 2 thermostats.

My first guess is that the gauges have a common voltage source.
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Old 23-07-2010, 16:36   #8
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I really doubt that both thermostats or temp. senders would go bad at the same time. Possible, but not likely. Is there anything in common on the instrument panel connecting the two gauges? If you can find out what the full scale deflection voltage is and then feed some voltage to the gauges, do they work? Its a lot easier to check them than it is to pull 2 thermostats.

My first guess is that the gauges have a common voltage source.
The same time is the puzzler First thought was electrical - but pretty sure both seperate. But that's not 100% sure

Feeding some voltage to the guages is an idea.........
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Old 23-07-2010, 16:47   #9
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That's a 13 year old engine? Sure is purty.
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Old 23-07-2010, 17:25   #10
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I really doubt that both thermostats or temp. senders would go bad at the same time. Possible, but not likely. Is there anything in common on the instrument panel connecting the two gauges? If you can find out what the full scale deflection voltage is and then feed some voltage to the gauges, do they work? Its a lot easier to check them than it is to pull 2 thermostats.

My first guess is that the gauges have a common voltage source.
^that

the thermostats are fine.

1) are you sure the coolant is topped? a gauge sensor will not measure air temp inside an engine.

2) ground the sender wire it will go full deflection on the gauge.
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Old 24-07-2010, 06:43   #11
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1) are you sure the coolant is topped? a gauge sensor will not measure air temp inside an engine.

2) ground the sender wire it will go full deflection on the gauge.
You know how to test senders & gauges, right?

Basic Engine Gauge Theory and Testing
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Old 24-07-2010, 06:46   #12
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You know how to test senders & gauges, right?

Basic Engine Gauge Theory and Testing

while I agree with the in depth testing procedure you've highlighted. Grounding the sending unit wire at the block end will give a "quick check" to determine if more investigation is necessary.
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Old 24-07-2010, 07:07   #13
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i agree with nevermonday. do you have 2 engines, and therefore 2 sets of t - senders and therefore 2 temp gauges on this boat? i find it quite unlikely that both sending units would conk out at exactly the same microsecond, or that both gauges would do likewise. so therefore i would look for what is common on both gauges. if both gauges are simultaneously reading zero then it has to be a bad common hot or common ground feeding the 2 gauges. i'd start at the gauges and work backwards, cleaning and dielectric'ing all the contacts into both gauges. look for a place in the wiring harness where either of those common wires for the gauges is wiggled loose or abraded.let us know what u find ...
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Old 24-07-2010, 14:00   #14
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Ok, cheers for all the input

Went onboard this afternoon, started the engines up and...............still the same

Anyway, we moved her accross the harbour to the winter berth for easy access and did some further investigations (albeit only on 1 engine)

As suggested (and because easy!) first step was to ground the temp sender to the block. Bingo! Guage comes to life!

Is my reading of that correct in that the problem must lie elsewhere?

Second step was to remove the temp sender (drained the system first) - the bit inside looks like a lump of copper - probably because it is? gave it a wipe sat and looked at it over a cuppa

Decided to see if connecting the temp sender back up (and turning both the batteries and ignition on ) and then dangling it into a cup of hot water did anything. Nope.

Then thought maybe it needs to be grounded - found a bit of wire and grounded it. Nope. Swapped the terminals over. Nope.

All told a good 5 miinutes in the hot water. and the copper end got hot enough not to want to hold, albeit not taking the skin off hot. Fortunately

My current question is - would testing the copper end of the temp sender in a cup of hot water actually give any results? If so would seem (to me!) that the problem is simply the temp senders....and therefore time to buy a new one and see what happens, before buying a 2nd for the other engine.

(my understanding is that the temp sender operates from simple expansion of the metal - no idea how the electrickery knows though with dissimilar metals inside brass? copper and electrickery could there be any electrolysis inside? even though no air? - science stuff not my forte )

BTW I can now identify the thermostat housing
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Old 24-07-2010, 14:07   #15
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I don't think you'll get a cup of water hot enough to register without a heating element.
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