Thermostat Question

[mrainey889]

Hello everyone. I have an issue with my current thermostat. The boat is a 1990 Rinker 18.5', 4.3 Mercruiser, Alpha One outdrive. When I bought this boat used water was leaking badly around the thermo housing. I removed the housing, cleaned up the surfaces, and replaced the two seals. While I had it apart I noticed the thermostat looked horribly dirty (lots of rust around it), so I decided to replace it. The thermostat was located about half-way up the housing and appeared to be retained by an o-ring. I removed the falling apart ring and saw that the thermostat was not going to leave willingly. Once I coaxed it out with a pair of needle nose pliers, I purchased a replacement. The new thermostat appears to be very close to the same diameter as the thermo housing, but not quite. It will not slide up in to the housing in the original position of the old thermostat.

My quick and dirty answer was to lay the thermostat in the same place it sits in a car engine (on the top of the motor block in the recessed ridge) and bolt everything back together. The result has been the engine will reach about 140* (spec'd temp of the thermostat) and then fall to the lowest part of the temp gauge. Then, if given enough time, the temp will return to about 140*, and fall again. Obviously the thermostat is opening and closing, but not producing the desired effect of maintaining proper operating temp.

The described condition is what the motor does at idle. If I let it warm up (say around 130*, before it starts dropping again) and take off across the lake the temp gauge plummets to the cold within a few seconds. As soon as the water pump is spinning fast the engine dives in water temperature.

All of the tells me I do not have the thermostat hooked up properly. What I want to know is:

How do I get the thermostat installed where the orginal thermostat was located?

- I know the o-ring is used to retain it, but how do I get it up there in the first place?

Do you have to used some kind of punch? Special tool? Was I sold the wrong diameter thermostat?

For what it's worth, the numbers on the original (and very bent up thermostat from my removing it) matched the numbers on the replacement I was sold.

Thanks again in advance, any help is appreciated.

Mike

 

[crazy charlie]

Re: Thermostat Question

most tstats have a retaining ring made of plastic or brass.this needs to be removed before the stat can be pulled out.
was there a ring in your housing??? I would take the old tstat and soak it in toilet bowl cleaner for 10 minutes so it is all cleaned up and put it back in and run the boat and see what the temp is.Get a manual for a diagram to help you.Charlie

 

[mrainey889]

Re: Thermostat Question

Thank you for the reply Charlie. No, there was no plastic or brass ring, only a rubber o-ring. The old thermostat was destroyed when I pulled it out with the pliers...bent all to hell. I have a Clymers manual for my boat and it simply says install the thermostat in the housing...no pictures and no further instructions, basically no help at all.

When I bought the new thermostat it came with a replacement o-ring, however I never used it since I could not get the thermostat in to the proper position.

Mike

 

[Don S]

Re: Thermostat Question

I have a Clymers manual for my boat and it simply says install the thermostat in the housing.

That explains it. You got suckered into buying a worthless manual.
Spend the money or look on ebay for the proper OEM Mercruiser Service manual. You need manual #7.
There are basically 2 different styles of thermostat housings used, Click Here and look at the Standard Cooling diagrams. Do you have the old or new design?

Either way, the thermostat does not go on the manifold. DO NOT run it that way. It must be where it's supposed to be.

 

[mrainey889]

Re: Thermostat Question

Thanks Don, per the diagrams on the web page you linked I have the "new" design. Two large hoses on the bottom, two smaller ones at the top with the nylon balls in them. All hoses enter from the sides.