Thermostat Problems

[CaptainPuget]

I’m having problems getting the right thermostat parts for a 1987 Johnson 70hp, or at least getting them to fit right. I notice that iboats and many other internet parts places do not carry parts for this year model. My local OMC shop sells me P/N 434137 ($29.50!) which doesn’t look much like my original T-stat but they tell me it supersedes the old one and will work fine. I also get the spring and the rubber seal that goes under the T-stat and the stainless steel retainer ring that fits in the powerhead and holds the rubber seal in place. In trying to re-assemble everything I notice that the retainer ring is too big to fit all the way into its place in the powerhead. I try the old one and I see that it is the same. It only goes in about halfway. I know this isn’t right but that’s the way it came apart so I put it back together that way and try it out. <br /><br />No good, still cold at idle. I take it apart and the rubber seal has pushed forward preventing a good seal with the plastic T-stat housing. So I go back to the OMC shop (60 mile round trip) and we double check all the parts and they match what the book calls out. No one knows of any bulletins on the issue and they don’t have any ideas. <br /><br />I’m out of ideas. This engine only had about 10 hours on it when I bought it several months ago so I’m pretty sure that I removed the original T-stat and it came from the factory with the seal not properly seated. The problem appears to be a design defect or maybe the powerhead was machined incorrectly. <br /><br />Has anyone encountered this problem before or have any suggestions for a solution?

 

[CaptainPuget]

Re: Thermostat Problems

^ Anyone?

 

[Dhadley]

Re: Thermostat Problems

The new T-stat should be black not white like the old one. The cap and spring are a matched set. There are a couple of caps and springs so make sure you have the correct ones.<br /><br />Not really sure what you mean by the rubber seal has pushed forward. It can only go so far into that hole it sets in.

 

[CaptainPuget]

Re: Thermostat Problems

The old T-stat was white, the new one is black. <br /><br />The problem is the stainless steel retainer ring that holds the seal will not seat all the way into the hole. That allows the rubber seal to move forward, not far, only about ¼ inch but enough to allow the plastic tip of the T-stat to bottom out on the SS ring and water leaks past.

 

[Dhadley]

Re: Thermostat Problems

Try it without the ss cup.<br /><br />You say its running too cold. What temp is it at? What is the problem that we're trying to overcome?

 

[CaptainPuget]

Re: Thermostat Problems

The problem is too cold at idle. I haven’t measured the temp but it is only slightly warm to the touch after several minutes at idle. Maybe 70-80 degrees at the warmest place on the engine. <br /><br />I’ll try it without the cup.

 

[Dhadley]

Re: Thermostat Problems

OK, its cool to the touch but what problem does that present that we're try to overcome? Does it idle OK?

 

[CaptainPuget]

Re: Thermostat Problems

It idled a bit rough. Nothing major, more for preventive maintenance than anything else I checked the T-stat and found what I’ve described. <br /><br />Leaving the ss cup out doesn’t work, too much slop. The T-stat is able to move around too much. <br /><br />I’ve cut four slits in the cup’s sides to allow it to deform annularly and pressed it in place with the seal. Seems to be holding. It warms way up now, maybe too warm. What temperature should it be at idle?<br /><br />It idles smoother now but I can’t keep my hand on the head for more than a couple of seconds.

 

[Dhadley]

Re: Thermostat Problems

I believe those t-stats are at 143. Check your service manual to be sure though.

 

[CaptainPuget]

Re: Thermostat Problems

Dhadley:<br /><br />Thanks for your help. I think that I have this problem behind me. <br /><br />My Clymer shop manual was not much help with this. It does tell me that the temp should be above 125F and below 163F and it has a bit of info on V-4 and V-6 T-stats, nothing on my particular model.