Really odd problem with t-stat/cooling system

danfinn · Jul 6, 2010

1994 4.3 LX, engine serial # 0f127354

The boat sat in a heated, dry garage all winter. The first trip out everything was normal. On the second day out I noticed that the water temp gauge was reading 200. The sender was replaced at the very end of last season and I'm really confident it's not the sender or the gauge acting up. I pulled out the old t-stat and ran it without that, it seemed to run fine and the water temp hovered right around 120 for another couple of days of use.

I ordered a replacement 160 degree t-stat from iboats and installed it along with a new o-ring and new gaskets this past weekend. Sunday when I took the boat out it hit 200 again. I stopped, popped out the t-stat and ran it without it for the day and again, everything seemed OK and the temp stayed right at 120. I thought maybe I got a bad t-stat but using boiling water on the stove at home I was able to watch the t-stat open and close so it seems to be working as expected.

Any thoughts on what could be going on here?

Thanks,
Dan

Bt Doctur · Jul 6, 2010

Re: Really odd problem with t-stat/cooling system

The condition of the impeller in the drive?????
The impeller was replaced when?????????
Manifolds and risers replaced last????????
should have shown almost no temp without a stat.Sounds like not enough water pumping thru the system

danfinn · Jul 6, 2010

Re: Really odd problem with t-stat/cooling system

Bt Doctur said:
The condition of the impeller in the drive?????
The impeller was replaced when?????????
Manifolds and risers replaced last????????
should have shown almost no temp without a stat.Sounds like not enough water pumping thru the system

To be honest I'm not sure when the impeller, manifolds or risers were last replaced. I know for a fact that I have not done any of that and I purchased the boat mid summer last year. The impeller is on my to-do list but I was hoping to be able to put that off for just a tad longer. How often are you supposed to replace the manifolds/risers?

120 is too warm with no t-stat?

HT32BSX115 · Jul 6, 2010

Re: Really odd problem with t-stat/cooling system

I purchased the boat mid summer last year. The impeller is on my to-do list but I was hoping to be able to put that off for just a tad longer.

ANY TIME you have an unknown impeller, it cannot be "put off" for any length of time!!

It should be first on any "to-do" list!!

Regards,

Rick

ADDED: If you're running in the Great Salt Lake, you should probably inspect/replace the manifolds/risers every 5 years or so.

In fresh water, they'll last for 15-20 years or more.....

danfinn · Jul 6, 2010

Re: Really odd problem with t-stat/cooling system

HT32BSX115 said:
ANY TIME you have an unknown impeller, it cannot be "put off" for any length of time!!

It should be first on any "to-do" list!!

Regards,

Rick

ADDED: If you're running in the Great Salt Lake, you should probably inspect/replace the manifolds/risers every 5 years or so.

In fresh water, they'll last for 15-20 years or more.....

Nobody actually takes their boat into the great salt lake, that I know of. It's something like 5x saltier than sea water, it would wreak havoc on a power boat.

What's a fair price for a mechanic to charge to do the impeller?

Bt Doctur · Jul 6, 2010

Re: Really odd problem with t-stat/cooling system

If the drive is not seized to the gimbal bearing
If the drive can be split for service
If the gimbal,bellows, U joints, engine alignment are all good
figure around $175.00 USD for parts,oil, labor

danfinn · Jul 7, 2010

Re: Really odd problem with t-stat/cooling system

Bt Doctur said:
If the drive is not seized to the gimbal bearing
If the drive can be split for service
If the gimbal,bellows, U joints, engine alignment are all good
figure around $175.00 USD for parts,oil, labor

Sounds good. I called the mech today but they are pretty backed up. Other than over heating, what's the risk of lightly running the boat as is with the t-stat removed?

danfinn · Jul 19, 2010

Re: Really odd problem with t-stat/cooling system

I got the impeller replaced, did it myself. Impeller replacement went smooth, no issues other than breaking the little connector clip for the speedo.

The old impeller looked to be in pretty good shape, it couldn't have been too old. No broken pieces, no cracks or dry rot.

Unfortunately this didn't fix my problem. With the t-stat re-installed and the ear muffs hooked up in the driveway, it still slowly climbed to 200.

It did seem like there was a small leak coming from somewhere around the up tube from the impeller housing but it was hard to see where it was coming from. I could feel surges in the intake hose coming into the t-stat housing but I wasn't sure if that was because it was hooked up to the muffs and not getting a proper water source to the intake vents on the outdrive. The seal that goes onto the drive shaft and slides down onto the impeller housing, that just slides down on top right? Because it kind of looked like that seal had a lip and should maybe be installed first into the impeller housing, then slid onto the shaft. Hopefully that makes sense.

I did it the same way this youtube video shows it being done (happens at 3:42):

http://il.youtube.com/user/liboatersclub#p/a/u/2/jXq35NOX8kw

If that's not causing the problem, where else should I be looking?

fossill · Jul 19, 2010

Re: Really odd problem with t-stat/cooling system

Why was the temp sender replaced last season? Overheat problems?

danfinn · Jul 19, 2010

Re: Really odd problem with t-stat/cooling system

fossill said:
Why was the temp sender replaced last season? Overheat problems?

No, it's never overheated since I've owned it. The temp sensor was replaced because I was getting some funky readings. Turned out to be the PO installed it with plumbers tape.

danfinn · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Morning bump, hoping someone has some suggestions.

CheeseCutter · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Don't even know if it's possible on this setup or would cause the problem, but is the thermostat upside down? And don't assume the way you found it is the way it should be....

danfinn · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Sure, I guess it's possible. This is the t-stat I bought:

And I've got it installed as it's showin the picture with the top of the image being the top in my t-stat housing. Rubber gasket goes in first, then t-stat, then this plastic spacer thing that holds it all in place.

HT32BSX115 · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Your raw water cooling system MUST have good water flow to work correctly.

The only way you'll KNOW that it has good flow is to check it.

Check it by installing a clear vinyl hose from the transom to the T-stat housing and observing the water flow thru it. Then disconnect the hose from the T-stat housing and then run the engine briefly to see how much flow you get out of it.

Those rubber impeller type (positive displacement) pumps will move a LOT of water.

There should be NO (or very few) bubbles in the water from the pump to the t-stat housing.

To ensure that it's working properly, you must do this in the water (in the lake).......... doing it with a flush adapter (muffs) won't cut it!

If you have good flow, then check the exhaust system.

The water from the head and block and water that doesn't go thru the T-stat (because it's fully or partially closed) then goes to the exhaust manifolds, to the risers and out with the exhaust.

If the exhaust manifolds or risers are plugged (with rust), then it cannot get out or will be severely restricted getting out. restricting the water flow out of the engine is every bit as bad as restricting it going in......total flow goes down........

danfinn · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

HT32BSX115 said:
The water from the head and block and water that doesn't go thru the T-stat (because it's fully or partially closed) then goes to the exhaust manifolds, to the risers and out with the exhaust.

If the exhaust manifolds or risers are plugged (with rust), then it cannot get out or will be severely restricted getting out. restricting the water flow out of the engine is every bit as bad as restricting it going in......total flow goes down........

Would this explain why it seems to run around 120 degrees with no t-stat installed? I was under the impression that the water all flowed out of the exhaust through the same exit.

CheeseCutter · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Rubber gasket goes in first, then t-stat, then this plastic spacer thing that holds it all in place.

Looks like the thermostat is positioned properly. There are two possible thermostat housings for that engine (see pics). Note the different order of the stat and sleeve in each one. You have the same order based on the housing you have?

danfinn · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Yeah, I have the one to the right and I have it installed correctly. Is there a diagram similar to that that shows me how the flow of the water cooling system works?

CheeseCutter · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

Is there a diagram similar to that that shows me how the flow of the water cooling system works?

Here you go...

HT32BSX115 · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

danfinn said:
Would this explain why it seems to run around 120 degrees with no t-stat installed? I was under the impression that the water all flowed out of the exhaust through the same exit.

ALL the water DOES flow out of the engine thru the same exit.......the exhaust manifolds & exhaust elbow(s)

There's no where else for it to go.

I don't have an explanation of why you're getting a particular temp. Unless you've checke the temp with a known gage, it might not even be 120*F etc....

When you don't use a t-stat, a LOT of strange things can happen. including hot spots, cold spots, steam pockets etc.....

If you have a lot of air bubbles in the water supply, you can get all kinds of problems (like above) too...

sethjon · Jul 20, 2010

Re: Really odd problem with t-stat/cooling system

First thing to check is make sure you didn't put the t/stat in backwards, a common mistake. Next, you may have to check the impeller.

Really odd problem with t-stat/cooling system

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