Temp Guage on 4.3 LX Mercruiser 2 wire

[kneedragger]

I have a 94, 4.3 liter LX, with the holley 4 barrell, Engine number 14099090M

My temp gauage is not working all of last summer, and I am trying to diagnose the issues. The intake manifold/thermostat housing has two wires one Brown w/ blue stripe (Starboard side) (i think is the temp Guage), and one solid brown (Port Side) leading to two different brass hex head sending units.

In reading searched posts on this subject, I understand to check to make sure the guage is working, to gound the wire to the block and see if it is pegged hot. However, most of what was researched only dealt with one wire.

I grounded both wires, and the guage does not move. However, If i bridge the wires together, I get a maximum hot reading on the guage.(hope I did not fry anything)

Also, with the motor NOT running, after a about 30 seconds, my alarm will sound.

First and foremost, I want to fix the guage, then worry about the alarm, and they may be connected.

What do each of these sending units do? Are they wired correctly, and can I test them?

Thanks for the help!

 

[Don S]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

That number you gave is a block casting number, not a Merc SN. Look just aft of the starter, there should be a brass tag rivited to the block.

The gauge sender has a single tan wire going to it. To test the gauge, disconnect the wire off the sender (tan wire), turn the ignition switch to run, the guage should be reading 0. Now touch the tan wire to ground. The gauge should peg out. If not the gauge or wiring to the gauge is bad. If it does peg the guage, you probably need a sending unit.

Your alarm may be ok. Some of them around that time used a timer in the alarm so it wouldn't go off when you first turn the ign sw on showing low oil pressure.

 

[kneedragger]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Don,

Thanks for the quick response. Try this number, OF266584. I will perform the task you mentioned above.

What does the Brown W/ Blue stripe go to?

If I do need to replace the sending unit, are there guidlines on temp ranges? Similar to a thermostat? Or are they all universal, and just work on ohm resistance?

 

[Don S]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Try this number, OF266584

That's more like it. You really do have a 94 engine. That doesn't happen too often around here.

What does the Brown W/ Blue stripe go to?

Look at the wires again and see if they aren't tan and blue. Brown is a lot darker (almost black) and used for the trim sender.

If I do need to replace the sending unit, are there guidlines on temp ranges? Similar to a thermostat? Or are they all universal, and just work on ohm resistance?

If you need to replace it, either get one from your Merc dealer, or get an aftermarket one that crosses to the Merc number, or you never will know if it's working right or not.

PS: Go up to the adults only sticky and download the OEM service manuals for your engine and drive. #18 for your engine, 14 for the drive.

 

[kneedragger]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Look at the wires again and see if they aren't tan and blue. Brown is a lot darker (almost black) and used for the trim sender.



Dang Don, your knowledge never ceases to amaze me. I call it brown, and you call it tan. But you are exactly right. (I REALLY hope that this does NOT come across as being condescending)

Now, what does this tan wire w/ blue stripe go to on my thermostat housing?

Thanks

 

[Don S]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

I call it brown, and you call it tan. But you are exactly right. (I REALLY hope that this does NOT come across as being condescending)

Not a problem, I know there are both in the wiring harness, Just making sure you are using the right ones.

 

[180shabah]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

The other wire is the switch for the high temp alarm.

 

[sdoomaha]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Had a similar problem with my '94 4.3...wasn't the guage, sending unit or wiring, it was the themostat locked closed. You can check your sending unit by applying heat...I just used a bowl of hot water then touched it to the block again to ground it.....found everything was working fine. I pulled my thermostat housing and checked the thermo in water heated on my stove...it never opened. If you look to see where the sending unit is located on the housing, it is on the "cool side" of the thermostat...if your thermostat never opens, the water heated by the block never reaches the sending unit, so it appears your motor is always running cold, or the guage isn't working. Replaced the thermostat in mine, and problem solved.

Good Luck...hope you get it figured out....

 

[kneedragger]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

I replaced both my thermostat, and sending unit this weekend. I plan to water test in a couple of months, and will post results.

I was able to rule out my guage simply by connecting the wire to the ground. My guage pegged hot.

 

[achris]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Common 'problem' with those engines (I had one) is that when someone replaces the thermostat they use a standard, off the shelf, automotive gasket. Then the temp gauge stops working. You need to use the genuine Merc gasket. It has a couple of ground continuity eyelets in it. The block that the temp sender lives in is isolated (electrically) from the engine block without the gasket continuity.... Merc gasket part number is 27-53045-1

The tan/blue wire is the alarm wire. There is another sender (which is actually just a switch), looks almost the same as the temp sender.... Are you sure you have the gauge wire on the right sender?

Chris.......

 

[kneedragger]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

Chris,

You are correct. Thanks for bringing that up.

I did use a mercruiser gasket with the four little brass "eyelets" on it. I fugureed these were for grounding purposes.

I also removed the old gasket material with a razor blade. After about 30-40 minutes of scraping, I finally used my air grinder with a wire wheel to remove the rest of the gasket material. Since it was cast iron, I can do that. I would not reccommend it with aluminum. In hindsight i should have done that to begin with. I HATE removing gaskets!! I am too impatient.

Anyway the surface was bright and shiney when I installed the new gasket.

I have two sensors on my thermostat manifold one (on starboard side) goes to the alarm. The other (on port side) goes to my temp guage, and this one is solid tan.

 

[achris]

Re: Temp Guage on 4.3 LX Mercruiser 2 wire

...I grounded both wires, and the gauge does not move. However, If i bridge the wires together, I get a maximum hot reading on the gauge.(hope I did not fry anything)...

Shouldn't have done any damage.... The reason the gauge pegged out is because there are several switches on the alarm circuit, one of which is oil pressure. With the engine not running that switch is closed, and creates a path to ground for the gauge.

Another test you can do is to ground the tan wire on the sender body (while it's screwed into the housing) and this will confirm you have a good ground path for the sender (continuity eyelets in the gasket doing their job).

Chris.........