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Old 24-07-2010, 14:16   #16
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Goto ➥ Basic Engine Gauge Theory and Testing
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Old 24-07-2010, 14:26   #17
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You know how to test senders & gauges, right?

Basic Engine Gauge Theory and Testing
no - not yet

Cheers
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Old 24-07-2010, 18:37   #18
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Methinks the sender must be grounded before it will work in a cup of tea.

Michael

Oops - you did ground it. Never mind...
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Old 25-07-2010, 14:35   #19
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Any progress on this David?
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Old 25-07-2010, 15:14   #20
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David, yes a hot cuppa is sufficient to test a temperature sender.

The sender itself is usually a "thermistor", that is, a resistor which changes value depending on the temperature. You test it by using a plain ohm meter set on a thousand-ohm scale. One test lead goes to the outside of the sender, the threads themselves, and the other lead goes to the terminal for the wire. (Usually the senders have one wire terminal and then make ground through the engine block.)

The resistance of a typical sender is 240 ohms at room temperature, and 40 ohms in a nice cup of near-boling water. Very rough numbers--they could be half or double that, it is the variation you are concerned with.

If the sender shows a similar variation from cold to hot, it is working. Sometimes they go dead, and I've had a Volvo sender go dead only to be replaced by a new DEAD one from Volvo, so if you do replace them, test the new ones as well.

The other sneaky problem could be that someone said "Gee, that was hard to replace" and installed those senders with some teflon tape on the threads. Teflon is an insulator, if the sender has to be grounded through the block--teflon will insulate it and you'll never get it to work. This must be a metal-to-metal contact on the threads. Antiseize is OK, teflon tape is not.

Since the temp meters peg when you ground the sensing wire directly to the block--the meters and all the wiring are OK, and the problem is in the senders. Could be one went dead, then the other, and over the past decade a PO just ignored them because Volvo parts can be, well, dear.
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Old 25-07-2010, 15:46   #21
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Any progress on this David?
Nope. It's Sunday Only discussions with Father (and he offers his thanks to all on the internet - however that works ).

Tommorow me Father will take the sender to the Marine Engineers / Volvo Dealer and get them to test - have a chat (he's known the boss for 20 odd years) - and unless they come up with any other plan probably order a new one............and keep fingers crossed that the problem is simply the temp sender. (why 2 at the same time? engines not used much over the last couple of years? maybe also they went a few months apart and as engines not used not noticed?)

BTW engines are 13 years old - father got them installed brand new (boat now 30 yo) and does his own routine maintanence / basic spanner work - but has thrown a mechanic at the engines on a couple of occassions over the years for a few things, albeit nothing major. Condition wise they look under 6 months old .........hopefully insides look the same............

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Old 25-07-2010, 16:06   #22
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... The resistance of a typical sender is 240 ohms at room temperature, and 40 ohms in a nice cup of near-boling water. Very rough numbers--they could be half or double that, it is the variation you are concerned with...
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Old 25-07-2010, 16:29   #23
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More or less ...
Unfortunately the circuit tester is very basic. Power on. power off.

Now it's off, the Engineer can bench test. Over (in?) a cuppa

Will let folks know on progress...........
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Old 01-08-2010, 12:56   #24
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Will let folks know on progress...........
Long story short

Temperature Sender was taken to Marine Engineers - tested it. said ok

Father said: Hmmmm..........I'll order 2 new ones please (£26 / USD40 for both.......figured that cheap and easy enough to fit into the category of might as well try even if a longshot - that money wouldn't get the Engineer half way to the boat, let alone tools out ).

Fitted both new Senders, fired the engines up - and the guages now work

Today took her for a run around the coast for 3 hours to her summer mooring and all ok

BTW just for general info, both (Volvo) engines have 772 hours on them, from new in 13 years - I guess the temp senders failed from old age rather than wore out But to be fair that includes well north to Paris and south to the Bay Biscay over that period. and a couple of years along the way of doing b#gger all

Father sends his thanks to all on the internet - he is now even thinking of joining the internet age himself. that's gonna be painful (for me)
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Old 01-08-2010, 14:45   #25
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Gord, it is interesting to see that EU senders are backwards from US ones. FWIW in my experience the Japanese ones follow US convention. Either way...

David, I'd suggest you fire up the old word processor and get some "certificate borders" at a stationery store. Then send each of those alleged engineers a large "Notice Of Revocation Of Engineering Credentials" signed date sealed stamped and made up in a suitably official manner.

Sometimes I wonder if the entire world has gone incompetent, or it they really ARE on a mission to waste everyone else's time.

What can you say, they're Volvo parts, they probably got homesick and then, when they heard that Volvo was bought out by the Chinese, died of despair.
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Old 01-08-2010, 15:22   #26
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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.
Munch, munch, munch....yechhhh
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Old 01-08-2010, 16:10   #27
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Munch, munch, munch....yechhhh
The next step was going to be back to the wiring up to the guages - as both senders going pop at same time did sound unlikely, but I guess they really went a few months apart (could even have been longer)

Went for £26 of senders as easier to DIY than chasing electrickery through spaghetti behind the dashboard

All ideas were greatly appreciated to help us muddle through / get a feel for being in the ballpark of the right track.

Double bonus on the mechanical front this week - the Triumph lives! 900cc of triple
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Old 01-08-2010, 16:30   #28
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Glad it worked out.

I once saw a Triumph with flames shooting out the vent hole in the gas tank cap and going at least 20' in the air. We had just come back from a trip to Ontario and my friend overfilled the tank and didn't clean up enough before he started the beast. The poor guy had just bought it from his brother a few weeks earlier.
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Old 15-04-2012, 23:51   #29
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Re: Volvo MD22 - errr, Where's the Thermostat ? :-)

I have red this topic with big interest, because I have quite a similar problem on my MD22L.
I have no temperature gauge, only the standard panel.
Problem: when the engine is started a few instants later (max. 1 minute) the temperature alarm is activated.
Actions done up to now:
checked temperatures with infrared thermometer (all OK!)
replaced the temperature switch (9) and the temperature sending unit (6) with new (expensive) volvo ones.
Suggestion of the volvo engineer: replace the complete electronic print
(costs 250 to 300 Euro) but no guaranties if it will eliminate the false alarm.
The alarm test on the panel works fine and I can switch off the soundbeep after starting, but the temperature alarm light stays flashing and what is the worst that I am not well informed if a real problem with engine temperature should occur.
Anybody with same experiences or suggestions to help me?
Looking forward to reactions
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Old 16-04-2012, 10:29   #30
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Re: Volvo MD22 - errr, Where's the Thermostat ? :-)

Wavelength, no specific ideas but if that "electronic print" is the usual, a strip of flexible plastic with printed circuit traces on it? And no components, just printed "wires" ?

Those are routinely repaired, no reason to replace them. If you can access it, or unplug it (carefully, sometimes the connectors are subtle and difficult to align), by all means take it out for a better examination. There's no magic there, just metallic traces that basically are wires. Either they are broken or unbroken, and if they are broken, you can carefully solder a jumper across them, or to bypass them. NOT a big deal, unless you are a mechanic charging $125/hour and don't want to invest an hour of your time.

I'd suggest getting a factory manual, or at least the circuit diagram, which would at least allow you to follow the circuit and see what might be tripping the alarm. Throwing random and expensive oarts at it often won't fix anything--like a simple short or broken wire someplace.
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