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Engine Block Temperature Temp Sender VS Temperature Sensor?

T

taymag

Contributing Member
My temp gauge reads too high (200-210) but the block reads normal with a temp gun, I decided to get a new gauge since my gas gauge went out last year I figured maybe that was but but it still reads the same.

So my question is, what is the difference in the Engine Block Temperature Temp Sender VS Temperature Sensor?

And lastly, since I am worrying about my engine temp, how can I test my overheat alarm?


Thanks:cool:
 
A "temp sender" or sending unit is supplying a signal for a gauge. The sender much match the gauge and the gauge (normally) reads a (in some senders) resistance (perhaps a total of say 200 ohm range to cover either cold through hot or a reading in degrees from low to high) and translates that into the reading. There are a few different (technologies), so the sender matched to the gauge is essential.

A "temp sensor", at least the one most commonly used by Merc (which might be more properly described as an overheat sensor) is really just a resistor that is preventing the alarm circuit from being completed. It is (off) at 170 degrees or less (so no circuit) and if the temp reaches 190 degrees it (turns on) the circuit goes to ground and your overheat alarm goes off - "beeeeeeeep". It's not feeding or supplying any (signal) back to anything that could be measured.
 
galamb said:
A "temp sender" or sending unit is supplying a signal for a gauge. The sender much match the gauge and the gauge (normally) reads a (in some senders) resistance (perhaps a total of say 200 ohm range to cover either cold through hot or a reading in degrees from low to high) and translates that into the reading. There are a few different (technologies), so the sender matched to the gauge is essential.

A "temp sensor", at least the one most commonly used by Merc (which might be more properly described as an overheat sensor) is really just a resistor that is preventing the alarm circuit from being completed. It is (off) at 170 degrees or less (so no circuit) and if the temp reaches 190 degrees it (turns on) the circuit goes to ground and your overheat alarm goes off - "beeeeeeeep". It's not feeding or supplying any (signal) back to anything that could be measured.
Click to expand...

Ok thanks, so if I have checked my motor/block temp all over with a heat gun (its at 150 or so), its peeing fine, I dont get an overheat alarm ever but it has always ran around 200 on the gauge (even after changing the gauge) should I replace the sender or check something else first?
 
I've never had any luck with a temp gauge on an outboard. It's not like an engine with a closed cooling system (or even half system) that you get on an IB or IO where you can accurately measure the temp.

I would suggest you are better off installing a water pressure gauge which will tell you "how well" your waterpump is working. That information is far more valuable then "what temperature" the block is at whatever exact spot your temp sender would be at. Since you can't measure the water circulating (continuously) around the power head, it really would be a "spot reading" that tells you little.
 
galamb said:
I've never had any luck with a temp gauge on an outboard. It's not like an engine with a closed cooling system (or even half system) that you get on an IB or IO where you can accurately measure the temp.

I would suggest you are better off installing a water pressure gauge which will tell you "how well" your waterpump is working. That information is far more valuable then "what temperature" the block is at whatever exact spot your temp sender would be at. Since you can't measure the water circulating (continuously) around the power head, it really would be a "spot reading" that tells you little.
Click to expand...

Thats true, but I feel like its "slightly" useful, even if the temp is 20 degrees off you would still know if it starts to rise

Aside from that, what is a fair price to get a pressure gauge installed?
 
A gauge might go in the 25-35 buck range if you don't want fancy. The sending unit is another 10-20 bucks and a "typical" shop would probably charge you an hour to do it.

So if you were quoted $150 bucks I wouldn't be surprised.

You could buy what you need off Flea-Bay for probably well less than 50 bucks and spend an hour or so of your time hooking it up yourself. Fishing the wire from the motor up to the dash is sometimes the most time consuming part.

But do pick your location for the sensor wisely. Again, because the "same" water is not continuously flowing around the power head, just because it's cool at one spot doesn't mean you aren't overheating at another. If you have a clog water channels surrounding cylinder 2 or 3 (or whatever) but your sender is located on the head/water jacket of number 1, you won't necessarily be aware of a problem.
 
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galamb said:
A gauge might go in the 25-35 buck range if you don't want fancy. The sending unit is another 10-20 bucks and a "typical" shop would probably charge you an hour to do it.

So if you were quoted $150 bucks I wouldn't be surprised.

You could buy what you need off Flea-Bay for probably well less than 50 bucks and spend an hour or so of your time hooking it up yourself. Fishing the wire from the motor up to the dash is sometimes the most time consuming part.

But do pick your location for the sensor wisely. Again, because the "same" water is not continuously flowing around the power head, just because it's cool at one spot doesn't mean you aren't overheating at another. If you have a clog water channels surrounding cylinder 2 or 3 (or whatever) but your sender is located on the head/water jacket of number 1, you won't necessarily be aware of a problem.
Click to expand...

What do you mean "pick your location for the sensor wisely", I am just replacing the sensor thats already there..
 
If you are simply replacing the temp sensor that is part of the alarm circuit then it goes where it goes.

In one of your responses above you left me with the impression that you were planning on going ahead with the installation of a sender that would feed a temperature gauge, say on the dash, which would give you a reading in degrees or even a more basic hot/cold reading - and that's what I was referring to when talking about picking a location for the sending unit.
 
I have one of them on my dink. Worked great for several years, but I had to replace the sender unit of late. Must be some commonality between manufacturers since I used a unit from a different source and it worked the same.

Jeff
 
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