Volvo Penta TMD40A oil alarm and expansion tank

[Nunuwawa]

Hello all

I recently bought a Storebro 31 with two Volvo penta TMD40A (1980) engines.
The oil alarm (what I think it is) from one of the engines doesn't work and I cannot find a similar one anymore
Does anyone know with what/how to replace this? (12V)
See attachments

Then I have another question
There is an expansion tank but I don’t understand how it supposed to work
Just under the pressure cap is an overflow outlet which is always open
How can any cool water pressure build up like this?
See attachments

Thanks a lot for any advice

Walter

 

[Nunuwawa]

Hello again
It looks it is a oil temperature sensor instead of oil alarm
Volvo part number

827151

1​

Temperature sensor

Thanks

Walter

 

[Leighb]

Welcome to SRC 31 ownership. There are two senders in the oil system, one for the pressure and the other is the alarm. There is no provision, on mine at least, for an oil temperature sender. A common problem with various of the engine circuits is a poor connection somewhere. Early on I had a scary moment when the oil pressure dropped to zero on one engine, which turned out to be a bad connection. Also the engine stop circuit failed, the button and the stop solenoid were fine, again it was the wiring in between.
it might be worth trying to make direct connection between the sender and the gauge and see if that resolves the problem? There are quite a lot of multi pin connector between the engine and the instrument panel.

 

[179580]

Hello again
It looks it is a oil temperature sensor instead of oil alarm
Volvo part number

827151

1​

Temperature sensor

Thanks


Walter

Oh no it is not.

 

[superheat6k]

I replaced the OEM oil pressure switch (not sender) with a switch I think from RS. I will see it I can find a reference for you.

Here you go ...

PS61-10-4MGZ-A-SP | Gems Sensors Hydraulic Pressure Switch, SPST-NO 15 → 60psi, 42 V dc, BSP 1/4 process connection | RS Components

 

[Plum]

Hello all

I recently bought a Storebro 31 with two Volvo penta TMD40A (1980) engines.

There is an expansion tank but I don’t understand how it supposed to work
Just under the pressure cap is an overflow outlet which is always open
How can any cool water pressure build up like this?

I don't know your specific engine (I have a 41) but the cap in your photo is not the pressure cap. I believe you have a pressure cap on top of the heat exchanger and, usually, the tube from there that goes to the expansion bottle you showed exits just above the main seal of the pressure cap. Above that main seal, and above where that tube exits, should be a secondary seal so that when the coolant cools it sucks what was pushed out into the expansion bottle back into the heat exchanger.

www.solocoastalsailing.co.uk

 

[RichardS]

I don't know your specific engine (I have a 41) but the cap in your photo is not the pressure cap. I believe you have a pressure cap on top of the heat exchanger and, usually, the tube from there that goes to the expansion bottle you showed exits just above the main seal of the pressure cap. Above that main seal, and above where that tube exits, should be a secondary seal so that when the coolant cools it sucks what was pushed out into the expansion bottle back into the heat exchanger.

www.solocoastalsailing.co.uk

This would be my assessment. If the vent pipe at the top simply connects to the air space, the pressure relief cap will be at the other end of the dip pipe which goes from the side of the tank.

Richard

 

[VicS]

I don't know your specific engine (I have a 41) but the cap in your photo is not the pressure cap. I believe you have a pressure cap on top of the heat exchanger and, usually, the tube from there that goes to the expansion bottle you showed exits just above the main seal of the pressure cap. Above that main seal, and above where that tube exits, should be a secondary seal so that when the coolant cools it sucks what was pushed out into the expansion bottle back into the heat exchanger.
www.solocoastalsailing.co.uk

That does not seem to agree with the parts diagram which lists the cap on the expansion tank as a pressure cap and the cap on the top part of the thermostat housing as just a plain filler cap,.
The angled pipe does not appear to come from the filler cap neck so is not the overflow associated with a pressure cap.
Its unclear where the hose from the bottom of the expansion tank goes but presumably somewhere around the heat exchanger / thermostat housing which will be pressurised

I would expect the little vent pipe on the expansion tank to be sealed or for a pressure cap which seats at the bottom of the neck to be fitted

 

[Plum]

That does not seem to agree with the parts diagram which lists the cap on the expansion tank as a pressure cap and the cap on the top part of the thermostat housing as just a plain filler cap,.
The angled pipe does not appear to come from the filler cap neck so is not the overflow associated with a pressure cap.
Its unclear where the hose from the bottom of the expansion tank goes but presumably somewhere around the heat exchanger / thermostat housing which will be pressurised

I would expect the little vent pipe on the expansion tank to be sealed or for a pressure cap which seats at the bottom of the neck to be fitted

I agree its a bit of a mystery but yes, the pressure cap is in the header tank (14 ín your picture) that is directly coupled to the heat exchanger and the expansion bottle (30) has a filler cap. I was assuming hose (41) enters between the pressure seal and the secondary seal of the pressure cap. If it does not, then its definitely a mystery!



www.solocoastalsailing.co.uk

 

[VicS]

I agree its a bit of a mystery but yes, the pressure cap is in the header tank (14 ín your picture) that is directly coupled to the heat exchanger and the expansion bottle (30) has a filler cap. I was assuming hose (41) enters between the pressure seal and the secondary seal of the pressure cap. If it does not, then its definitely a mystery!

www.solocoastalsailing.co.uk

I assume the pressure cap is similar to this one
Different shaped tank with a "vent " to the left connected back to the top of the heat exchanger ( radiator in this case)

The tank neck is plain, with no inner seat, the cap only seals on the top of the neck. If it overflows it does so all over the top of the tank... but in 40 years it has never overflowed

 

[Plum]

I assume the pressure cap is similar to this one
Different shaped tank with a "vent " to the left connected back to the top of the heat exchanger ( radiator in this case)

The tank neck is plain, with no inner seat, the cap only seals on the top of the neck. If it overflows it does so all over the top of the tank... but in 40 years it has never overflowed

View attachment 115097 View attachment 115098 View attachment 115099

The pressure cap is the silver coloured one towards the front of the engine above the heat exchanger in the picture in post #9

 

[VicS]

The pressure cap is the silver coloured one towards the front of the engine above the heat exchanger in the picture in post #9

According to the parts description that just a filler cap. Its the one on the expansion tank which is described as a pressure cap.

 

[Nunuwawa]

Thank you all

I will try to find where exactly the bottom hose from the expansion tank goes to

Regarding the oil alarm sender
Volvo has (had) a 12v and a 24v version
I thought it is just a contact but if there are two version something more is involved?

I did a little test trip yesterday and one engine overheated and I saw a lot of water
came out, will check today where it was coming from.
Also this engine made a strange metallic sound the first minutes, this suddenly stopped, strange……
The engine seemed to work normal.

Thanks again

Walter

 

[Nunuwawa]

I assume the pressure cap is similar to this one
Different shaped tank with a "vent " to the left connected back to the top of the heat exchanger ( radiator in this case)

The tank neck is plain, with no inner seat, the cap only seals on the top of the neck. If it overflows it does so all over the top of the tank... but in 40 years it has never overflowed

View attachment 115097 View attachment 115098 View attachment 115099

pressure cap looks just the same, only different color

 

[RichardS]

pressure cap looks just the same, only different color

That is definitely a pressure relief cap but I can't be sure that it has a return vacuum valve in the centre as there is no sealing ring around the central valve but it could seal against something inside the neck of the expansion tank. We would need a photo down the neck of the tank to be sure but my view is that it does not have a vacuum return as the internal boss is not sprung or deep enough and that it simply allows excess pressure out through the central valve via a drilling to one of the four side lugs.

Either way, that raises the issue in #7 about whether that small plastic pipe at the top really does go into the open air space at the top of the tank. If it is simply a vent into the open space then the cap is not doing anything at all. If it is an open vent, I wonder whether the tanks are supplied with that vent pipe sealed in the moulding which gives installers the option of drilling out the plastic depending upon the type of installation required and in your case the vent has been incorrectly opened by a previous owner?

Richard

 

[VicS]

pressure cap looks just the same, only different color

ITYWF that the colour is a code that identifies the pressure, but they are marked anyway. (Mine is 75 kPa)

 

[VicS]

That is definitely a pressure relief cap but I can't be sure that it has a return vacuum valve in the centre as there is no sealing ring around the central valve but it could seal against something inside the neck of the expansion tank. We would need a photo down the neck of the tank to be sure but my view is that it does not have a vacuum return as the internal boss is not sprung or deep enough and that it simply allows excess pressure out through the central valve via a drilling to one of the four side lugs.
Richard

It definitely does have a vacuum release valve.

The centre unit can be removed and I have, many years ago, taken it apart to find out how it works, but I am not going to do so again.

 

[RichardS]

It definitely does have a vacuum release valve.

Does the central valve also release excess pressure in the expansion tank? Surely it can't operate in both directions?

If it does release pressure, where does it vent the excess pressure to?

If it does release the vacuum, where does it suck the air from?

Richard

 

[VicS]

There is a little vacuum release valve (A) in the centre of the main pressure control valve

The vents ( B ) are where excess pressure is released and where air is drawn in to release the vacuum

(Modern replacements may not be the same)

 

[RichardS]

There is a little vacuum release valve (A) in the centre of the main pressure control valve

The vents ( B ) are where excess pressure is released and where air is drawn in to release the vacuum

(Modern replacements may not be the same)

View attachment 115229

View attachment 115230

Interesting. I did suggest that the B lugs were vented to atmosphere but I've never seen a pressure relief valve and a vacuum release valve combined into one fitting like that.

It's a clever construction which, if the little plastic tube has indeed been opened out into the expansion tank air space, is totally wasted.

I might be tempted to block off the plastic tube and see what happens.

Richard