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Discussion Starter #1
Ordered a new one from Center,ine. The sensor is about 1/2 " diameter in threaded area. It is way too small for the cyl head; existing one is at least twice that .
Anyone know where I might find the right one? There are many shown on E Bay parts, but none look like the one in my cyl head now.

Chief Bre9
 

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But Mad North-Northwest
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So I'm going from memory on the L-jet Spiders, but pretty sure your car has three senders: one for the Bosch injection system, one for the gauge, and one for the warning light. The former two are on the right side of the engine and the warning light one is at the top center rear of the head. Which one are you trying to replace? Sounds like you either bought the wrong one or are looking at the wrong one on the car.
 

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Discussion Starter #3
So I'm going from memory on the L-jet Spiders, but pretty sure your car has three senders: one for the Bosch injection system, one for the gauge, and one for the warning light. The former two are on the right side of the engine and the warning light one is at the top center rear of the head. Which one are you trying to replace? Sounds like you either bought the wrong one or are looking at the wrong one on the car.
So I'm going from memory on the L-jet Spiders, but pretty sure your car has three senders: one for the Bosch injection system, one for the gauge, and one for the warning light. The former two are on the right side of the engine and the warning light one is at the top center rear of the head. Which one are you trying to replace? Sounds like you either bought the wrong one or are looking at the wrong one on the car.





Trying to replace the water temp sensor on top of the cylinder head, just back of # 4 spark plug. Every one I have looked on line shows the 1/2" diameter sensor I received today from Centeer,ine, which is way too small to replace the existing one.

Chief Bre9
 

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But Mad North-Northwest
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That's a water temp sensor on top of the head, yes, but that's only for the high temperature warning light. Orange/black wire.

The one you bought is a sender for the gauge. That's somewhere on the right side of the head with a single brown wire.

You sure your gauge isn't reading right? May want to use an Ohmmeter and measure cold resistance vs. the new one you bought before you replace it. If they're the same then the sender isn't your problem.
 

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Discussion Starter #5
So I'm going from memory on the L-jet Spiders, but pretty sure your car has three senders: one for the Bosch injection system, one for the gauge, and one for the warning light. The former two are on the right side of the engine and the warning light one is at the top center rear of the head. Which one are you trying to replace? Sounds like you either bought the wrong one or are looking at the wrong one on the car.
I'm probably looking at the wrong one; I shorted the one behind #4 plug to ground & the overheat light on the dash lit up. So, where on the right side of the engine is the one connecting to the water temp gauge on the panel? Other blog says it has a single brown wire....
 

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But Mad North-Northwest
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I'm probably looking at the wrong one; I shorted the one behind #4 plug to ground & the overheat light on the dash lit up.
Yeah, I said that.

Other blog says it has a single brown wire....
I said that too. Try and keep up, Chief :D

I think this post has the right info. In post #1 you can see it at the very right, just under the big black hose. In post #2 it's sender 41 in the diagram. It'll be the one with a single brown wire.


If you ground the brown wire the gauge should go full scale. If that's good then measure the cold resistance relative to your new sender: if they're pretty close then likely your existing sender is fine. What issue are you having with the gauge reading?
 

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as Tom says, you are looking for this one.
First though, I'd make sure the wire is even connected, and also that it is clean.
If you do need to swop it out, you will lose some coolant.

temp gauge sender.jpg
 

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Discussion Starter #8
That's a water temp sensor on top of the head, yes, but that's only for the high temperature warning light. Orange/black wire.

The one you bought is a sender for the gauge. That's somewhere on the right side of the head with a single brown wire.

You sure your gauge isn't reading right? May want to use an Ohmmeter and measure cold resistance vs. the new one you bought before you replace it. If they're the same then the sender isn't your problem.
I'll look again today, using the pic sent on one of the blogs. The gauge only shows 110 degrees with a fully warm
engine. Radio shop checked it externally with an infra-red gauge showing 185 degrees when warm.

Chief Bre 9
 

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Discussion Starter #9
That's a water temp sensor on top of the head, yes, but that's only for the high temperature warning light. Orange/black wire.

The one you bought is a sender for the gauge. That's somewhere on the right side of the head with a single brown wire.

You sure your gauge isn't reading right? May want to use an Ohmmeter and measure cold resistance vs. the new one you bought before you replace it. If they're the same then the sender isn't your problem.






radiator shop used infra red sensor showing 185 degrees & gauge at 110. I'll measure resistance today.

Chief Bre 9
 

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do as Tom says
remove the single brown wire and ground it (Ignition ON obviously)...... the instrument gauge needle should go right up to max.
If it doesn't - then it's no use replacing the sender, as the problem lies elsewhere.
 

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Discussion Starter #12
Yeah, I said that.



I said that too. Try and keep up, Chief :D

I think this post has the right info. In post #1 you can see it at the very right, just under the big black hose. In post #2 it's sender 41 in the diagram. It'll be the one with a single brown wire.


If you ground the brown wire the gauge should go full scale. If that's good then measure the cold resistance relative to your new sender: if they're pretty close then likely your existing sender is fine. What issue are you having with the gauge reading?
Gubi, at 83 I don't move as fast as I used to. It's Hell to get old, but the good news is 1: Wife & I got our Covid shots today, and, 2. Finally found the brown wire(it had a black plastic jacket on), hooked up a long wire w/alligator clips, & shorted it to ground & sure enough gauge went full scale! Why they had to bury it under all the hoses & wires, I don't know. So now, more unbolting until I can get a wrench on & looks like I will lose some coolant in the process. How close do you recommend the cold distances should be new/one old one?

Chief Bre 9
 

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Discussion Starter #13
do as Tom says
remove the single brown wire and ground it (Ignition ON obviously)...... the instrument gauge needle should go right up to max.
If it doesn't - then it's no use replacing the sender, as the problem lies elsewhere.
Finally found it, & gauge goes all the way. Now I have to find all the wrenches to get all the other pieces out of the way!

Chief Bre 9!
 

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Just poking fun, Chief. Glad you can still work on the Alfa at 83!

These are some data I took on a sender that I think is the same as the one on your car. Not 100% on this, though, so be careful how much you trust me.

In thinking about it, if you know the car's running at 185 probably best to measure resistance of the in-car sender when hot. That'll be more useful and accurate than measuring at room temperature. So with the car at operating temperature, I think you should see about 250 ohms on the sender if it's good. If it's bad it'll probably be around 1000 ohms if the gauge is reading 110F.

Again, I could be wrong with these data as I took them a long time ago...

1667651
 

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Discussion Starter #15
Just poking fun, Chief. Glad you can still work on the Alfa at 83!

These are some data I took on a sender that I think is the same as the one on your car. Not 100% on this, though, so be careful how much you trust me.

In thinking about it, if you know the car's running at 185 probably best to measure resistance of the in-car sender when hot. That'll be more useful and accurate than measuring at room temperature. So with the car at operating temperature, I think you should see about 250 ohms on the sender if it's good. If it's bad it'll probably be around 1000 ohms if the gauge is reading 110F.

Again, I could be wrong with these data as I took them a long time ago...

View attachment 1667651
Here are the numbers: New, out of box sensor: 2.265 ohms; old one still in cylinder head: 3.862 ohms. So, I still don't know how to interpret these numbers, since they are so far from what is in your chart. These are when the car is cold.
I started to take the old one out, but space is so tight I did not have a 7/8"/3/8' drive socket to do it.

Chief Bre 9
 

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Discussion Starter #16
Here are the numbers: New, out of box sensor: 2.265 ohms; old one still in cylinder head: 3.862 ohms. So, I still don't know how to interpret these numbers, since they are so far from what is in your chart. These are when the car is cold.
I started to take the old one out, but space is so tight I did not have a 7/8"/3/8' drive socket to do it.

Chief Bre 9
 

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But Mad North-Northwest
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I'd assume your Ohmmeter is reading kOhms, so that would be 2265 and 3862 Ohms respectively. It does seem like the one in the car is reading higher than expected and might be bad.

If you really want to make sure, drive the car until it's fully hot and see what it measures hot, should be like 250 Ohms I think.
 

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Discussion Starter #18
I'd assume your Ohmmeter is reading kOhms, so that would be 2265 and 3862 Ohms respectively. It does seem like the one in the car is reading higher than expected and might be bad.

If you really want to make sure, drive the car until it's fully hot and see what it measures hot, should be like 250 Ohms I think.
I can probably do that when the 24 degree weather abides.
 

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Discussion Starter #19
I'd assume your Ohmmeter is reading kOhms, so that would be 2265 and 3862 Ohms respectively. It does seem like the one in the car is reading higher than expected and might be bad.

If you really want to make sure, drive the car until it's fully hot and see what it measures hot, should be like 250 Ohms I think.
I can probably do that when the 24 degree weather abides.
 

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Here are the numbers: New, out of box sensor: 2.265 ohms; old one still in cylinder head: 3.862 ohms. So, I still don't know how to interpret these numbers, since they are so far from what is in your chart. These are when the car is cold.
I started to take the old one out, but space is so tight I did not have a 7/8"/3/8' drive socket to do it.

Chief Bre 9
Would your readings have been done at room temperature and might be 2.265 and 3.862 Kohms? Or thousand ohms, 2265 ohms and 3862 ohms?
Sorry, Tom beat me, didn’t mean to repeat.
 
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