Is Thermostat causing my temp guage issue? *Update - Fixed*

[Scag]

Thought I had either a bad temp guage and or sending unit because the needle was only moving about a milimeter above 0 degrees...However I was able to rule out the guage by grounding the wire running to the sending unit...guage pinned all the way over to the right as it should. Sending unit has been replaced. I had the boat in the shop for an unrelated problem and I told them to basically check what I checked and see if they had different results. They didnt, so the guy suspected that my thermostat was stuck open and it was causing the engine to not get to operating temp.

Does this make sense? This was over the phone...haven't gone to see them yet, perhaps I misunderstood what he was saying. Any ideas?

Thanks in advance!


P.s. Engine is a y/m2001 4.3L mercruiser.

 

[dubs283]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

verify temp at the sender with a temp gun - this will tell you if your t-stat is operating correctly

did you replace the sender?? did you use sealant on the threads??

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

I'm trying to track down a temp gun now!

What sealant would you recommend? I did replace the sender...I'll do it again, this time with sealant!

 

[Don S]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Any paste type thread sealer will work. I usually just use some gasket sealer. DO NOT use teflon tape, it can prevent good electrical contact between the sender and the engine.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Thanks Don, I'll give it a shot this weekend.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Does anyone know a good way to get this "sleeve" out (the grey ring around the rusty thermostat)? It seems to be holding the thermostat in...I just don't want to force anything and break it.

 

[Don S]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Many times rust builds up behind the insert. Breaking them may not be avoidable.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

I got it!!! I had sprayed some pb blaster on it and let it sit for an hour...wouldnt budge so I sprayed more and let it sit probably another hour or two. Came back at it with a pair of pliers...I was standing on it and pulling up at the same time and it finally came out....and didnt break! I'll be putting everything back in tomorrow evening.

Thanks for all the help.

 

[OldNBold51]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

In case your new t-stat didn't work, I chased the temp gauge problem all last year doing much the same as you....new t-stat, another sending unit (2nd in a year) etc. My problem was the aftermarket sending units weren't compatible with gauge. 3rd attempt i installed the OEM sending unit and it works like a champ.

 

[NHGuy]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

If you don't have good ground to the temp sender-which comes through the thermostat housing, you can have this issue. I think I remember the t-stat gasket on my motor has a brass grommet on it to help facilitate the ground.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

UPDATE:

Ok, well I finished the Thermostat swap using the Sierra 18-3647 kit which included all the gaskets, orings, etc....I ended up having 3 leftovers as they were not applicable to my setup. I followed the service manual found in the "adults only" section. and everything went smoothly.

Started the engine up (on the muffs) and within a few minutes, my temp guage arrived at the 160 degree operating temp!!! I've had no guage for about a year now, so I was pretty pumped. Then the guage creeped past 160 all the way up to about 190. I turned up the hose water pressure and the guage seemed to go down to about 180-185. Engine is running SO smooth now....I guess it has been running cold for so long and I never realized the true effect on the motor.

I am going to test in on the river this weekend. Do you guys think its normal to run a little hotter on the muffs?

 

[JWebber]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Hows your impeller?

 

[Don S]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Do you guys think its normal to run a little hotter on the muffs?

It's possible, if you don't have a large volume of water, or low pressure from your hose, it may overheat. Many times too long a hose will do it. Even with good pressure and volume of water at the hose bib, by the time you go through 100 ft of hose, it's pretty weak and will probably overheat.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

Hows your impeller?

Brand new. Preplaced 2 weeks ago by a shop. I had hit a rock with my s.s. prop and the insurance ended up covering my prop and prop shaft. Had new seals/berrings/impeller put in.

 

[Scag]

Re: Is Thermostat causing my temp guage issue?

Re: Is Thermostat causing my temp guage issue?

It's possible, if you don't have a large volume of water, or low pressure from your hose, it may overheat. Many times too long a hose will do it. Even with good pressure and volume of water at the hose bib, by the time you go through 100 ft of hose, it's pretty weak and will probably overheat.

Went out today and the needle stayed pegged at about 180. Was definitely cooler than the day I ran it on the hose, but not quite at 160. I am sure it is the correct sierra thermo stat...double checked the part# and it had 160 printed on the bottom of it. I guess I have to get a temp gun and measure the temp at the thermostat to varify the guage is accurate. Am I on the right track or would you suggest something else? Is 20 degrees warm TOO warm? Motor seems to run SUPER smooth compared to when it was running cold.