Water temp - 4.3L - SOLVED

[jurasicjet]

Hello:<br />I recently had a water leak that was traced to the thermostat casting, lower gasket. After removing the casting and carefully and thoroughly cleaning the surfaces, I re-installed new gaskets. Leak solved. Now, however, I have a new problem.<br />I have basically no water temp. While in the lake, I removed some of the hoses to make sure that I have water flow, I do. I can get it up to maybe 115deg. F., but that is it. Before it would run at around 130-140 or so. <br />My housing has two temp probes in it. One on the port side and one on the starboard side. The one on the port side has a tan/blue stripe wire on it, the one on the starboard side has just a tan wire. Is it possible (ok, anything is possible) that I somehow jarred those sensors and now they don't work or did I get a piece of rust, etc. in the thermostat and now it is full open?<br />Thanks

 

[achris]

Re: Water temp - 4.3L - SOLVED

Hi JJ,<br /><br />May I call you JJ?<br /><br />The 2 sensors you see are temperature sensors, but one is for the gauge and the other is a switch for the alarm. The other thing to know about that housing setup is that the gaskets should have had a couple of brass eyelets in them. This is for ground continuity. The sensors ground through the body and into the thermo housing, then through the gasket eyelets and onto the engine block.<br /><br />Hope this helps.<br /><br />Chris................

 

[jurasicjet]

Re: Water temp - 4.3L - SOLVED

Hey Achris:<br /><br />Thanks!!<br /><br />I think that helps alot. You are correct about the one sensor for the alarm and the other is for the gauge. Interestingly enough, I replaced the gaskets with automotive gaskets, thinking no big deal, and I know that they didn't have any brass eyelets in them. I guess I'll head to the marina tomorrow and buy the correct gaskets. <br />Thanks again!

 

[achris]

Re: Water temp - 4.3L - SOLVED

Another happy customer.

 

[Don S]

Re: Water temp - 4.3L - SOLVED

I doubt it Chris...... Wonder why those steel bolts on that housing and into the manifold don't make the contact.<br />Funny that only Mercruiser uses those rivets, not Volvo or anyone else.

 

[achris]

Re: Water temp - 4.3L - SOLVED

Originally posted by Don S:<br /> I doubt it Chris...... Wonder why those steel bolts on that housing and into the manifold don't make the contact.<br />Funny that only Mercruiser uses those rivets, not Volvo or anyone else.

I thought those bolts were non-conductive. <br /><br />I have actually seen this fault on another boat Don. The guy had cut gaskets from a sheet himself, got the same funny temp gauge readings. Put the proper gaskets in and BINGO, gauge works again!!!<br /><br />Chris..............

 

[jurasicjet]

Re: Water temp - 4.3L - SOLVED

Well... I guess tomorrow it will be time to get out the ohm meter and see what those bad boy bolts are made out of. I'm guessing steel. <br />The sensor had some corrosion on it when I replaced the gaskets. Could knocking that corrosion off create a problem with the sensor? Looks like the sender is just a probe and nothing more. Is there a way to check the sensor (ohm, etc.)?

 

[Don S]

Re: Water temp - 4.3L - SOLVED

The ground for the sender is through the base/threads of the sender. Even something like teflon tape (Uck) will cause false readings.<br />Might also get one of those laser heat guns at Sears or your local autoparts and check the actual temp right next to the sensor. Could be a stuck thermostat.

 

[waterone1@aol.com]

Re: Water temp - 4.3L - SOLVED

Could you please post what year your engine is ? Are you shure that you re-assembled everything correctly ? Some years used plastic spacers that went on before the thermostat and if installed incorrectly would cause some wild temp problems. As for the brass eyelets, put an ohn meter on the thermostat housing. Scrape off a little paint and put one probe on the housing the other on a clean bolt or metal on the engine, if you see more than 1 or 2 ohms of resistance, that could be your problem...if not...thats not it.

 

[jurasicjet]

Re: Water temp - 4.3L - SOLVED

The engine is a 1992. Serial number F076691.<br />The only thing that I did to the thermostat housing was replace the top and bottom gaskets. I did not remove the thermostat or any of the sensors/senders. That is why I was rather baffled on why there was no temp reading after replacing just the gaskets. <br />Should the ohm reading be taken when the engine is cold or at operating temperature, or doesn't it matter?

 

[waterone1@aol.com]

Re: Water temp - 4.3L - SOLVED

It really shouldn't matter what the temp is. All you are trying to do is make sure that your temp sender is getting a good ground. I have always used the factory gaskets with the brass eyelets. Without them, you are depending on the mounting bolts to "carry" the ground. The ohm meter will tell you if that is working or not.

 

[jurasicjet]

Re: Water temp - 4.3L - SOLVED

Well.... for what it's worth...<br /><br />Achris was correct. The MARINE gaskets do have some very small brass rivets the provide continuity to the temp sensors. The bolts, are not enough to do this. Maybe if you had a new boat with no corrosion on any component, just the bolts would work. But, with an older boat that has rust on the inside of the thermostat housing and bolts that have some rust on them, it just isn't enough. And, even if you did get everything cleaned up, the vibration of the engine engine may potentially work it into such a postion that you loose the ground again (the bolts are not "tight" in their respective holes).<br />I discovered this by grounding the base of the sensor to a good ground on the engine block via a length of wire. The temp gauge went from 120F to 175 instantly. Hmmmm. Ground problem. So, since I have it apart again I will be installing a new thermostat and the correct marine gaskets.

 

[garycinn]

Re: Water temp - 4.3L - SOLVED

The same thing happened to me on my 2001 4.3L TBI Merc. Cut my own gaskets -- no temp. Put in the rivet Merc gaskets -- gauge works.