Running with a Clogged Thermostat

[jmburock]

I just opened up my thermostat panel on the back of my 1989 Mariner 75hp 3 cylinder for the first time since I've owned it (5 years). When I opened it, I found the thermostat was clogged with sand/ corrosion and obviously not functional. The poppit valve large gasket was also falling apart. I replaced both with new parts, new gasket, etc. after cleaning out all the old crud and running it for a couple minutes with the housing off.

How would this have affected my engine performance since the thermostat was not functional? I never noticed any significant problems other than some light fouling at the plugs...

 

[Silvertip]

Re: Running with a Clogged Thermostat

It should have run hot at idle and more than likely hot at wide open throttle as well. Are you sure the warning horn works??

 

[jmburock]

Re: Running with a Clogged Thermostat

My warning horn has been disconnected since I've bought the motor as the VRO has been disabled and I've been running pre-mixed fuel, therefore I don't know if it's been running hot or not. I've never had any problems in the 5 years I've run it that I know of, other than occ. difficult cold starting and some plug fouling. Would this have caused any permanent damage that I might not be aware of?

 

[Silvertip]

Re: Running with a Clogged Thermostat

Cold starting problems are common on Mercs (and other two stroke engines as well) and are very often due to "operator error" more than anything else. Sorry if that bites a little. As for plug fouling, that could be caused by a thermostat and/or bypass valve that is stuck open causing over-cooling. An over cooled engine can also "cold seize" meaning it can seize up if you go wide open throttle without a very long warm up period. What happens is the hot pistons expand at a different rate than the over cooled block so everything just tightens up. Is it common? Not very -- but it does happen. An over cooled engine will not operate efficiently and may show poor idle quality. As for the Overheat alarm I need to say shame on you (sorry again -- I just can't help it). Fixing that alarm may result in saving you a power head. Its a pay a little bit now situation vs paying a ton more later to replace the power head.

 

[jmburock]

Re: Running with a Clogged Thermostat

I agree with you on the lack of warning horn. Where do I find the actual horn on my 89 Mariner 75hp (OC170850). WOuld it be in the Quicksilver Commander shifter unit or is it somewhere on the engine???

 

[Texasmark]

Re: Running with a Clogged Thermostat

Location of horn depends on your remote. Not in the engine. Either in the control box (Commander 2000 identifiable by fast idle lift lever), or under the dash, or laced into the wiring harness....near the remote control (both options with the Commander 3000 identifiable by having to push the big black button in, on the shift handle, to get fast idle).

Go to the head of your engine (close to where your spark plugs mount) and look for a (size of a dime) cover with one screw with a tan or tan/blue, or maybe even black wire coming from it. That is your OH sensor. To sound the constant OT alarm it shorts to ground.
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I am reading out of a service manual which goes back to '94 (3 cylinder engines) so there could be some differences in the colors you see and what I say but you can follow the sequence anyway.

( I had an '89 115 which was an old design I6.....don't know what the 75 hp engine was like that year....don't know if it was the old 4 cyl or the new 3 cyl design. If the 3 cyl,the following will probably be easier to understand than if it's the old 4 cyl........I'm not sure the 4 cyl had a thermostat and warning buzzer.......
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Follow the wire to the junction block...probably on the starboard side of the engine (should have two stud posts on it with that wire, and a tan, and tan blue wires connected. If you had VRO, (oil tank mounted on engine) you will have the junction block (only purpose was to pick up the additional wire from the oil alarm). If not, and you have an OT sensor the wire may go directly to the remote harness plug and pin 2 is probably your baby.

With ign key on, take a piece of 14 or 16 AWG wire and short to the engine block (from the terminal block) insuring that you get good connections. If you don't have a block and the wire is solid to the connector you will have to disconnect the connector and short from the connector pin to ground.....only in an application where there is no separate oil reservoir.......requiring you to premix oil-gas.

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If you have no OT switch (like on old 4 cyls) non of this will apply and you and you didn't hear a horn because there is nothing to activate it.
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The horn should sound a constant alarm. If not you have a problem:

Problem could be no 12v to the horn (purple), or broken wire back to the junction block(tan/blue). Purple is the color of the 12v feed to the horn and tan/blue is the ground side going back to the engine thru the engine's remote connector (Pin 2) to the junction box you just came from.

The other wire there is tan from the warning module and sounds the horn if you have an oil problem.....I guess your engine had VRO. Otherwise this last wire is not there.

So there are 3 senario's I took you through, 3 different engine designs....no OT, OT without VRO, and OT with VRO. Your engine will be one of them.

HTH

Mark

 

[jmburock]

Re: Running with a Clogged Thermostat

Mark- thanks for the long reply. I have the 3 cylinder version 75hp. I have an OT sensor, and oil module warning box but no speaker/horn to be found. I have the Quicksilver Commander remote (no fast idle lever) and the horn is not in there. Maybe it is under my dash or located in the boat hull. If not, guess I need to buy an alarm horn module to install. This is the problem with buying a used motor- never know what the prior owner did to modify it from original...

 

[Texasmark]

Re: Running with a Clogged Thermostat

Just like old farm tractors. You never know what mouse had set up housekeeping. Grin

Mark

 

[jmburock]

Re: Running with a Clogged Thermostat

Just like old farm tractors. You never know what mouse had set up housekeeping. Grin

Mark

Being a New England Yankee I'm not exactly sure what this means ? Any other phrases I might better understand ?

 

[Texasmark]

Re: Running with a Clogged Thermostat

Just something I threw in. What it means is you never know what was done by the previous owners and what was their competence level. Sometimes they put it back (in working order) like it was. Other times you have to rip it all out and start over......and just because "the book says".......doesn't mean a thing if it's been cobbled up.

Mark

 

[marty53]

Re: Running with a Clogged Thermostat

My 2 cents:

I have basically the same engine as you (91 75hp). Before I got my new control --commander 2000 with warmup lever I didn't have a warning horn either. I found that out the easy way because as soon as I installed my new control I now have a constant overheat alarm going off I never knew about. I was tempted to just disconnect the wires but I know I shouldn't do that.

So I may be in the same boat as you--no pun intended. It makes you wonder how many people are running in alarm state without knowing it? I still am not sure how to turn mine off-- see my other post from this morning.

Marty