Can't find a replacement Coolant Temperature Sensor

[JonL]

1990 MerCruiser 4.3L 175HP V6 Alpha One: Engine Model OD392581; Engine Serial Number OD 410228: Sea Ray.

I have two temperature sensors on the thermostat housing. I can find the Water Temperature Sender (smaller one) all day long, but it is impossible to find the Coolant Temperature Sensor (longer one). Does anyone know where to find one, or the part number for this item.

My engine becomes unstartable once the engine warms up and runs awhile. If I turn it off hot, it won't start properly. This started after it overheated from a bad impeller. I'v replaced the impeller and the thremostat, but cant find the Coolant Temperature Sensor to replace it. The porcilen around the outside broke off so I need to replace it. Does this even seem like it could be the problem? I'm hoping it's not the rings in the engine cause it seems to run just fine when it's cold.

I've read here that one of the sensors/senders sends info to the ECM. Is that true? Does my MerCruiser have a ECM? And which sensor exactly is it that sends the signal to the ECM versus the temperature gauge on the dash?

In Case I don't get back here regularly I'd appreciate an email (EDIT Removed email address)

Thanks
Jon

 

[Don S]

Re: Can't find a replacement Coolant Temperature Sensor

According to your serial number, you have a carbed engine, you don't have an ECM, that is on EFI engines only.
One of your senders is for the gauge, the other (smaller one) is an alarm switch which sound the audio alarm under the dash.

 

[stonyloam]

Re: Can't find a replacement Coolant Temperature Sensor

Does this help? http://www.mercruiserparts.com/Show...desc=WIRING+HARNESS+AND+ELECTRICAL+COMPONENTS (#7)

 

[JonL]

Re: Can't find a replacement Coolant Temperature Sensor

Yes you are right, it is carbed. Thanks for that info. How do I find the coolant temperature sensor then that works the guage? I have searched the internet to no avail. Went into NAPA auto parts with the sender/sensor and they had not seen one. I found one in a NAPA Marine Products catalog, but it has a plug connector at the tip and mine has a threaded post with a lock washer and a single nut. Can I use the same sensor in each side of the thermostat because the threads look the same, and I don't really care about the alarm since I always drive with one eye on the temp gauge.

Also any idea why my engine won't start when it is hot. I know water is circulating bacause I ran it with the outdrive in a tub of water and hot water was exiting properly?

But really need to know where to find this sensor?

Here is a picture of both sensors. each one has only one wire coming off the top. I'm not positive which is the sensor vs. the sender?

http://landoncpa.net/Images/sensors.jpg


Thanks Don

 

[JonL]

Re: Can't find a replacement Coolant Temperature Sensor

What you sent looks like the water temperature "sender"; the one in the top of my image; and does that go to the gauge or alarm?

The one in the bottom of my picture must be the coolant "sensor"? And goes to the alarm? That is the one I cant find.

 

[stonyloam]

Re: Can't find a replacement Coolant Temperature Sensor

There are 3 #7s listed, the bottom one sure looks like it.

 

[JonL]

Re: Can't find a replacement Coolant Temperature Sensor

Yes thanks, I'm trying to find the top one. They both came out of my thermostast housing. There is one on each side? The bottom one in my picture has a plastic or porcilin piece on top about 1/2 inch. the third no. 7 Don shows doesn't have that, and looks more like the one on the top in my picture?

Are all these thermostate housings different ??

 

[achris]

Re: Can't find a replacement Coolant Temperature Sensor

The 2 sensors in the thermostat housing are NOT the same. One is a switch for the alarm, has a Tan/Blue wire attached and its part number is -48952. The other is a sender for the temperature gauge and there are 2 variants. One has 3/8"-18TPI, part number -97257A1 and the other is 1/2"-14TPI, part number -97258A1. (The third sender listed in the diagram is for dual station installations ONLY)

Regardless of whether the sender and switch are working or not, they have no effect on the engine starting. If you have had an overheat the first thing to do is a compression check. You may have softened the piston rings, or even blown a head gasket.

Chris...........

 

[JonL]

Re: Can't find a replacement Coolant Temperature Sensor

Thanks Chris...never would have found the sensor without your help.

I was afraid someone was going to say the rings are gone.

Jon