Beta Marine 35/38 coolant temperature sensor.

[pete.i]

I believe the coolant temperature sensor on my engine has packed up. It is difficult to tell because it only lights an LED on the control panel when the engine reaches a critical temperature. Anyway the engine doesn't appear to be overheating as I have checked it with one of those laser thermometer doobrys. As I don't think an LED indication is a particularly good idea I had this idea to change to a temperature guage system. I have removed the old sensor and it does appear to read open circuit which ever way I use the meter probes. So I bought a new sensor from Beta Marine at the ridiculous price of £55, in case I cannot convert to a guage. Unfortunately on testing it it also seems to read open circuit. These sensors have two connections. One goes to the case and reads short circuit. The other, I would have thought, should read a resistance, depending on how hot it is, between it and the case. I cannot read any resistance between that contact and case no matter what ohms range I set my meter on, nor whether the sensor is hot or cold. I have tried it in boiling water and with a heat gun. Am I barking up the wrong tree with these particular sensors or do they not work resistively? I have ordered a sensor and guage of Ebay which I am hoping I can use instead of the present system but the new sensor from Beta Marine was in case it all goes pear shaped.   

[john6767]

Ours is a Beta 35 with just the basic control panel, ie only the warning light/buzzer for over temperature.  I have thought about adding a temp gauge and looked at the sensor and there is on a wire on one of the connections.  I was assuming that the other connection could be used with a temp gauge?  I would be very interested to understand if that is correct and if you could use any gauge or do you have to buy one from Beta, which I am assuming will be more expensive.

[pete.i]

Both the sensors that I have are the two terminal type. These were fitted to engines pre 2005 according to Beta Marine. After 2005 the sensor only has one terminal. The guy I spoke to at Beta Marine says these sensors are not interchangeable although I cannot for the life of me understand why other than the fact that my control panel has LED indicators and the post 2005 control panels seem to have incandescant bulbs.

 

Anyway on my sensors (both) I read a dead short between the unused terminal and earth, chassis, deck whatever we want to call it, and if I connect the LED wire to it the LED is lit at all times. On the other terminal, on both sensors, I read an open cct and the LED stays off at all temperatures. So my understanding of how engine coolant temperature sensors work has taken a bit of a blow. Unless, of course, both the sensors are faulty. I have ordered a sensor and matching gauge off Ebay (£5 ish) which, hopefully, has the correct thread and I will be fitting that. So when that is done, I will report.

 

But I still have the enigma of the original and original (stupidly expensive) new sensors that do not seem to work.

[john6767]

Our boat was built 2005, it for sure has two terminals on the sensor. Please provide an update of how you get on.

[Neil2]

2 hours ago, pete.i said:

I believe the coolant temperature sensor on my engine has packed up. It is difficult to tell because it only lights an LED on the control panel when the engine reaches a critical temperature. Anyway the engine doesn't appear to be overheating as I have checked it with one of those laser thermometer doobrys. As I don't think an LED indication is a particularly good idea I had this idea to change to a temperature guage system. I have removed the old sensor and it does appear to read open circuit which ever way I use the meter probes. So I bought a new sensor from Beta Marine at the ridiculous price of £55, in case I cannot convert to a guage. Unfortunately on testing it it also seems to read open circuit. These sensors have two connections. One goes to the case and reads short circuit. The other, I would have thought, should read a resistance, depending on how hot it is, between it and the case. I cannot read any resistance between that contact and case no matter what ohms range I set my meter on, nor whether the sensor is hot or cold. I have tried it in boiling water and with a heat gun. Am I barking up the wrong tree with these particular sensors or do they not work resistively? I have ordered a sensor and guage of Ebay which I am hoping I can use instead of the present system but the new sensor from Beta Marine was in case it all goes pear shaped.   

Unless or until someone else sheds light on it I believe your understanding is correct. There should be resistance when the sensor is cold but no resistance if/when the coolant reaches a "critical" temperature.  Unfortunately I am not on my boat at the mo otherwise I could run your tests as I know for certain my sensor (kubota engine) works... (another story).   I wonder if, when you have tried to get it to open, the water temperature isn't high enough, maybe it's set slightly above boiling point?  It's a crude comparison but the whistle on our kettle doesn't sound until the kettle has been boiling for quite a while, maybe you need to give the sensor a bit longer to fire?  Clutching at straws here...

 

I'm looking at replacing the alarm sensor with a guage and as I understand it it's a simple mod, just a case of getting the right size thread on the new sensor - just out of interest where did you get yours?   

 

 

[Boater Sam]

If its a basic panel with just an LED temperature light, the "sensor" is just a switch, OPEN circuit until too hot then it switches on, one terminal is connected to ground, enfine, t'other goes to the LED which has 12v on the other side.

 

With a temperature gauge it is a different sensor, its resistance to ground decreases with rising temperature, only one wire.

 

So your switch (sensor) will not go short circuit till the engine is too hot. Then the LED will come on.

[pete.i]

34 minutes ago, Neil2 said:

Unless or until someone else sheds light on it I believe your understanding is correct. There should be resistance when the sensor is cold but no resistance if/when the coolant reaches a "critical" temperature.  Unfortunately I am not on my boat at the mo otherwise I could run your tests as I know for certain my sensor (kubota engine) works... (another story).   I wonder if, when you have tried to get it to open, the water temperature isn't high enough, maybe it's set slightly above boiling point?  It's a crude comparison but the whistle on our kettle doesn't sound until the kettle has been boiling for quite a while, maybe you need to give the sensor a bit longer to fire?  Clutching at straws here...

 

I'm looking at replacing the alarm sensor with a guage and as I understand it it's a simple mod, just a case of getting the right size thread on the new sensor - just out of interest where did you get yours?   

 

 

I haven't got it yet but I have ordered one from Ebay. The one I have ordered is a sensor and gauge as I think the sensor has to be matched to the gauge to give the correct readings. The stupidly expensive sensor I got from Beta Marine. I did leave both sensors in actually boiling water for a good few minutes and also played a heat gun on them for a minute or so. I didn't see any change in the multimeter readings in either case. As you say it will be the thread which is critical on the replacement gauge and sensor. My sensor is actually screwed into an adaptor on the engine block and that is from new because the green paint covers both the sensor and the adaptor.

 

This is the one I have ordered. Cheap as chips because it may not work so I didn't want to go expensive. It says it is digital which it obviously isn't LOL.

 

 

 

https://www.ebay.co.uk/itm/2-52mm-Digital-Car-Water-Temperature-Gauge-40-120-LED-Universal/283447330287?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

 

Hopefully that thread size will work. We shall see.

6 minutes ago, Boater Sam said:

If its a basic panel with just an LED temperature light, the "sensor" is just a switch, OPEN circuit until too hot then it switches on, one terminal is connected to ground, enfine, t'other goes to the LED which has 12v on the other side.

 

With a temperature gauge it is a different sensor, its resistance to ground decreases with rising temperature, only one wire.

 

So your switch (sensor) will not go short circuit till the engine is too hot. Then the LED will come on.

It's a bit late then which is why I want to change it to a gauge/sensor config. But your explanation does sound plausible. What is the purpose of the grounded terminal? this isn't on the newer engines.

Edited May 6, 2019 by pete.i

[john6767]

5 minutes ago, Boater Sam said:

If its a basic panel with just an LED temperature light, the "sensor" is just a switch, OPEN circuit until too hot then it switches on, one terminal is connected to ground, enfine, t'other goes to the LED which has 12v on the other side.

 

With a temperature gauge it is a different sensor, its resistance to ground decreases with rising temperature, only one wire.

 

So your switch (sensor) will not go short circuit till the engine is too hot. Then the LED will come on.

So are you saying that the second unused terminal on the sensor is not for when a gauge is used?

[pete.i]

2 minutes ago, john6767 said:

So are you saying that the second unused terminal on the sensor is not for when a gauge is used?

I cannot see how it can be as it is a direct short to earth. If Boater Sam's explanation is correct that will explain why I am not getting the readings that I thought I should. I suppose, thinking about it, just to light an LED it doesn't need a varying resistance although what the purpose of the grounded Terminal is I have no idea.

 

[john6767]

1 minute ago, pete.i said:

I cannot see how it can be as it is a direct short to earth. If Boater Sam's explanation is correct that will explain why I am not getting the readings that I thought I should. I suppose, thinking about it, just to light an LED it doesn't need a varying resistance although what the purpose of the grounded Terminal is I have no idea.

 

I guess I has just assumed that the engine had the sensor to drive the gauge, so that it would work with either instrument panel.   Certainly to drive the led it just needs to be a switch, so i guess it could be a different sensor for the two panels and the one that is installed has the second terminal as a ground.  On the panel with the temp gauge I though that there was also a warning light though.

[Neil2]

It's just occurred to me that the these sensors must be set to work with a 50/50 mixture of antifreeze, so presumably they won't set off the alarm/light until the coolant reaches the boiling point of the antifreeze mixture, - higher than water. 

 

Is this why testing the sender in plain boiling water doesn't work?

 

[Boater Sam]

25 minutes ago, Neil2 said:

It's just occurred to me that the these sensors must be set to work with a 50/50 mixture of antifreeze, so presumably they won't set off the alarm/light until the coolant reaches the boiling point of the antifreeze mixture, - higher than water. 

 

Is this why testing the sender in plain boiling water doesn't work?

 

Partly, but mainly because you have a pressurised cooling system, pressure increases the boiling point. So the sensor probably closes slightly over 100 deg C.

You are not on the top off a high mountain with your kettle are you?

[Tony Brooks]

That extra terminal is probably to make it "marine" spec. and price so punters think it is insulated return.

 

[john6767]

So it looks as though there is a different sender on the engine if you have a gauge or just a light, but it does say that pre 2007 the two connector one that is a switch and sender was standard.  If the OP’s like ours have the two connector one it does suggest that should be for a gauge and there I assume variable resistance with temp. Was the replacement part number 200-01133?

 

The parts list for Beta 35, 38 and 45 is here https://issuu.com/betamarine/docs/b35_to_b45t_spares_list?e=15614309/61277963

 

one of the relevant pages showing the cooling system parts

 

 

 

[pete.i]

11 hours ago, Neil2 said:

It's just occurred to me that the these sensors must be set to work with a 50/50 mixture of antifreeze, so presumably they won't set off the alarm/light until the coolant reaches the boiling point of the antifreeze mixture, - higher than water. 

 

Is this why testing the sender in plain boiling water doesn't work?

 

I would think that that is absolutely correct. Bear in mind that I assumed it worked like a normal sensor and that I should have read a varying resistance. having said that I did test my old one with a heat gun and that got it proper hot and still nothing changed. I didn't test the stupidly expensive one (£55) that I got from Beta Marine with the heat gun.

 

@john6767   Yes that is the same parts list that I have. I got the dates wrong I said 2005. Anyway I was told that the newer sensor wasn't compatible with my engine (2000) but that may be just because I haven't got a gauge. I'm not prepared to spend another silly amount of money to test that theory though just yet. I'm going with the cheapy from Ebay, which hasn't arrived yet, for now.

Edited May 7, 2019 by pete.i
To add summat else

[Boater Sam]

1 hour ago, Tony Brooks said:

That extra terminal is probably to make it "marine" spec. and price so punters think it is insulated return.

 

That did occur to be but as the "extra" terminal is connected to the body of the switch it makes a nonsense of an insulated return engine i.e. marine spec. I wonder if Beta know that?

[john6767]

1 hour ago, pete.i said:

I would think that that is absolutely correct. Bear in mind that I assumed it worked like a normal sensor and that I should have read a varying resistance. having said that I did test my old one with a heat gun and that got it proper hot and still nothing changed. I didn't test the stupidly expensive one (£55) that I got from Beta Marine with the heat gun.

 

@john6767   Yes that is the same parts list that I have. I got the dates wrong I said 2005. Anyway I was told that the newer sensor wasn't compatible with my engine (2000) but that may be just because I haven't got a gauge. I'm not prepared to spend another silly amount of money to test that theory though just yet. I'm going with the cheapy from Ebay, which hasn't arrived yet, for now.

But the interesting thing is that pre 2007 it is the two connector switch/sensor one and post 2007 the single connector switch one.  That really does suggest that if you have a two connector one it will drive a gauge.  I guess it need to get a meter out.

[Iain_S]

The sensor marked 050 (Part No 200 -01133) drives both a warning lamp and a gauge. The smaller spade terminal drives the gauge and there should be a resistance between it and the case. The standard 1/4" spade drives the lamp, and is open circuit unless there is an overheat condition, when it goes short circuit. Not sure of the temperature it switches at, but it could well be over 100 degrees C.

 

If the OP's sender is open circuit, and the warning LED is coming on, then there may be a short to ground somewhere on its connecting wire.

[Tony Brooks]

1 hour ago, Boater Sam said:

That did occur to be but as the "extra" terminal is connected to the body of the switch it makes a nonsense of an insulated return engine i.e. marine spec. I wonder if Beta know that?

Probably but the glow plugs, starter etc are also usually earth return despite in some cases looking like insulated return. I also question how many alternators really are insulated return and not just earth return with a negative terminal on the case.

[pete.i]

1 hour ago, Iain_S said:

The sensor marked 050 (Part No 200 -01133) drives both a warning lamp and a gauge. The smaller spade terminal drives the gauge and there should be a resistance between it and the case. The standard 1/4" spade drives the lamp, and is open circuit unless there is an overheat condition, when it goes short circuit. Not sure of the temperature it switches at, but it could well be over 100 degrees C.

 

If the OP's sender is open circuit, and the warning LED is coming on, then there may be a short to ground somewhere on its connecting wire.

I think that the appearance of one terminal being shorter than the other in that picture is just camera angle. The original one off my boat and the stupidly expensive new one I got from Beta Marine both have terminals of the same length. Also on both of the senders that I have there is absolutely no resistance between the earthed terminal and earth, or body of sender. I did bite the bullet and use a heat gun on the new sensor I have and the switched terminal does indeed switch when it gets hot enough. The earthed terminal does absolutely nothing. So I am convinced that a gauge will not work with this sender under any circumstances. I know it says "sender" but both mine only "send" a make or break condition to the LED from one terminal. The other terminal is permanent earth and if I connect the LED to that it is permanently lit for all conditions.

[Boater Sam]

13 minutes ago, pete.i said:

I think that the appearance of one terminal being shorter than the other in that picture is just camera angle. The original one off my boat and the stupidly expensive new one I got from Beta Marine both have terminals of the same length. Also on both of the senders that I have there is absolutely no resistance between the earthed terminal and earth, or body of sender. I did bite the bullet and use a heat gun on the new sensor I have and the switched terminal does indeed switch when it gets hot enough. The earthed terminal does absolutely nothing. So I am convinced that a gauge will not work with this sender under any circumstances. I know it says "sender" but both mine only "send" a make or break condition to the LED from one terminal. The other terminal is permanent earth and if I connect the LED to that it is permanently lit for all conditions.

So its exactly  as I said several posts ago? The eathed connection is unnecessary on your boat,just ignore it.

[pete.i]

And I haven't disagreed with you Boater Sam. I initially thought that it was a "proper" sender which it isn't. It's just a switch. I am ignoring the earth terminal and always have. It's one or two of the other posters that seem to think it will power a gauge. Their's may well power a gauge. Mine, one of which is brand spanking new bought at a silly price from Beta Marine, will most definetly not power a gauge. As I am now aware of that, thanks to you, I am in the process of purchasing a cheap Chinese knock off gauge and sender. Unfortunately it has to come from China so it wont be here just yet. But when it does I will post on the outcome of that wait.

[john6767]

2 hours ago, pete.i said:

I think that the appearance of one terminal being shorter than the other in that picture is just camera angle. The original one off my boat and the stupidly expensive new one I got from Beta Marine both have terminals of the same length. Also on both of the senders that I have there is absolutely no resistance between the earthed terminal and earth, or body of sender. I did bite the bullet and use a heat gun on the new sensor I have and the switched terminal does indeed switch when it gets hot enough. The earthed terminal does absolutely nothing. So I am convinced that a gauge will not work with this sender under any circumstances. I know it says "sender" but both mine only "send" a make or break condition to the LED from one terminal. The other terminal is permanent earth and if I connect the LED to that it is permanently lit for all conditions.

Just to clarify the new one is part number 200-01133, which is supposed to be a switch and sender, something wrong here..

[pete.i]

7 minutes ago, john6767 said:

Just to clarify the new one is part number 200-01133, which is supposed to be a switch and sender, something wrong here..

Dunno all I know is that there is absolutely no way in the world that the two senders I have, one of which is a brand new on from Beta Marine, will drive a gauge. obviously the old doesn't work at all because it is faulty but the new one only turns on when enough heat is applied to it. There is no change in resistance whatsoever until the thing switches. It is either off or on. The other terminal is straight to earth and doesn't change in any way from a short condition.

 

Anyway new sender and gauge has just arrived from China. So I will be fitting it tomorrow and I will come back on this thread and let you know how it goes.

11 minutes ago, john6767 said:

Just to clarify the new one is part number 200-01133, which is supposed to be a switch and sender, something wrong here..

 

[Iain_S]

2 hours ago, pete.i said:

I think that the appearance of one terminal being shorter than the other in that picture is just camera angle. The original one off my boat and the stupidly expensive new one I got from Beta Marine both have terminals of the same length. Also on both of the senders that I have there is absolutely no resistance between the earthed terminal and earth, or body of sender. I did bite the bullet and use a heat gun on the new sensor I have and the switched terminal does indeed switch when it gets hot enough. The earthed terminal does absolutely nothing. So I am convinced that a gauge will not work with this sender under any circumstances. I know it says "sender" but both mine only "send" a make or break condition to the LED from one terminal. The other terminal is permanent earth and if I connect the LED to that it is permanently lit for all conditions.

It's not the length, it's the width. The switch is on a 6.35mm spade, the temp. sender one is smaller, 4.1mm, I think.

 

I did check one once, and, if I remember right, the resistance of the gauge terminal to body was about 150 Ohms.