Thermostat necessity question

[Texasmark]

Just bought this boat and have had it out 3 times in the past 60 days. As mentioned in another post, the thermostat was stuck closed and I limped home.<br /><br />Since Merc did without them long after OMC introduced them I said what the heck and tossed it.<br /><br />Was out again yesterday and in cold weather this engine is really thirsty trying to get her going at launch. I thought that maybe I should put another stat in.<br /><br />But I have a couple of objections to that (thoughts/questions).<br /><br />1. Upon entering the lake with a cold lake and cold engine, the stat will do absolutely nothing to help you get you started the first time. Will agree that subsequent starts could be easier, but they are easier anyway. Like touch the key and she's a running, no throttle advance necessary.<br /><br />2. This engine has a water pressure relief valve that is forced open when you plane out and get some water pressure on the water inlet holes in the skeg. Opening this valve bypasses the thermostat and allows lake water to run freely thru the engine's cooling passages.<br />---------------<br /><br />So if I'm running flat out it's useless and unless I stop and troll for awhile, or putt around at near idle speed I get no benefit from it.<br /><br />So did I miss something?<br />----------------<br /><br />Then there's the matter of temp. The pellet on mine was stamped 120 degrees. Noticed at least 1 www site that has after market stats for sale and you can get some hotter ones. But if you get too hot your cooling passages are like a hot water heater and build up scale and plug. Any thoughts here? I realize that 120 degrees is warmer than a 40 degree lake, but I already went thru that.<br /><br />Thanks,<br /><br />Mark

 

[Paul Moir]

Re: Thermostat necessity question

There's at least a couple very good reasons for thermostats that I can think of, not having to do with warm starts or happy idling. First, consider a smaller outboard that doesn't need the bypass/relief valve.<br /><br />The cylinder walls change shape sligtly depending on their temperature, due to the expansion of the metal. It's different in different in different places due to support web, etc. The thermostat allows the bore to be worn in a predictable way that fits the rings since the hot wear pattern will be different from the cold wear pattern. <br />With better fitting rings, there's more power and less blow by of exhaust gasses past the piston. <br /><br />Ever hear about warming up the engine before a compression test? It does make a difference, even though the air in the cylinders is quit a bit less dense (due to the heat).<br /><br />Also with a consistant bore shape, wear is much less. It's hardly scientific, but in the J/E forum we see far more (thermostated) 40hp engines in good shape compression wise than (not thermostated) 33 or 28hp engines. It's not unusual for the 33 or 28hp to have bad or marginal compression.<br /><br />The other big reason is cold seizure. Since consistant temperature allows for consistant bore size, the pistons can be much more closely fitted to the bore. This gives a number of benefits. The exhaust ports are better sealed allowing better crankcase sealing (better idle and fuel efficiency). Heat transfer from the piston to the engine is better which helps keep the melt-limit of the piston in check. Noise due to piston slap is much less.<br />Now with this closely fitting piston and bore, take the thermostat out of the engine. The piston's tempurature hasn't changed, but the bore's has. It's gotten colder and now it's smaller. The piston can (and does) expand to the point where the thin oil barrier between it and the bore is defeated. The piston is scuffed and worn away, and if it's really bad the piston's skirt can collapse slightly. After that it never returns to it's efficient shape.<br /><br />Unfortunately, on big engines they can't run enough water through the constriction of the thermostat, so it's bypassed at higher rpms. The spring is calibrated though to attempt to maintain a consistant block temperature. This is easily seen. If you run around at full throttle, and put your hand on the block, it'll be warm.

 

[Bigjohn1]

Re: Thermostat necessity question

You don't mention what year engine and what technology (2-stroke, 4-stroke carb, 4-stroke efi) - IMHO, it depends. If I had a classic 2-stroke in a year-round warm climate, I'd promptly toss the t-stat at my first opportunity - for some of the reasoning you site. No way would I do that with the newer 4-stoke efi's (regardless of climate). Too much impact on the fuel management system as a whole.

 

[Texasmark]

Re: Thermostat necessity question

It's a '02 90 hp 3 cyl 2 cycle Merc. Having lost one engine ('75 rude 70 hp) to a stuck stat and had it not been for the warning horn this would have been 2; I have never had to rebuild a 2 cycle for any other reason.<br /><br />But I do understand your reasoning Paul. I'm located in N. Texas and most of my boating is in the summer. Just get the itch sometimes in the winter and about an hour of that is all that I can take.<br /><br />Thanks guys for your inputs and time.<br /><br />Mark

 

[Paul Moir]

Re: Thermostat necessity question

I don't think it matters much to the engine if the cooling water is 60F instead of 32F. <br />Warning systems are vital as you can just as easily loose an engine to a bag, etc.

 

[Laddies]

Re: Thermostat necessity question

Tex, it don't matter if it's a themostat or a warning system, if the manufacterer could save $.02 in building the engine by not having the item on the engine and the unit function properly it would not be there

 

[Texasmark]

Re: Thermostat necessity question

Don't laugh!!<br /><br />Had a washing machine built in good ole USA in the '60's by Philco PFFFFFFFORD. Had 3 bearings on the main shaft. Had a failure. Learned about bearings in this caper.<br /><br />Anyhew, located the bearings and found out that the OEM bearings weren't sealed; sealed bearings were 5 cents more; 15 cents per washer.<br /><br />PFFFFFFFAAAATTTT American manufacturing!<br /><br />Mark

 

[Paul Moir]

Re: Thermostat necessity question

Oh man, that's not the Philco frontloader with something like 500lbs of cast iron and a pair of dampners bolted to tje drum to keep it from dancing because it had a 4000 RPM spin cycle?

 

[Texasmark]

Re: Thermostat necessity question

Naw this was a top loader. The agitator went up and down to wash. Only used the bearings when the spin cycle arrived.<br /><br />But I remember an old Bendix front loader with the see thru door that mama had when I was a kid.<br /><br />Must have been a pretty good washer as dad never worked on it and I think we had it as long as I can remember.<br /><br />Mark

 

[BillP]

Re: Thermostat necessity question

Running cold will let crud build up in the ring lands and on piston crowns. Eventually a ring can stick or break. When it builds on the piston crown hot spots can happen and burn a hole through the piston. The piston deal happened to me on a 140hp v4 omc when running without a tstat. Water temps were in Florida so they weren't that cold (75-85F)The first thing I noticed when taking the tstat out was poor idle. 1000 hrs later (without decarbing)one piston died. Lesson learned was to decarb often if running without a tstat. I was using regular tcw rated oil but it may be cleaner to use synthetic oil when running without a tstat.

 

[Texasmark]

Re: Thermostat necessity question

Interesting, Bill.<br /><br />I sold an 18ft trihull with a '72 125 Johnny once. Had a 17 or 19 SS prop (don't remember) on it for skiing. Would do 39; but had no tack so didn't know rpm's. Wasn't over propped as it would pull 2 slaloms up outta da hole smartly with the rest of the family in the boat. <br /><br />Ha! Just remembered. Once on a company picnic, we wanted to see what it would do and we lifted 5 skiiers with it, outta da hole. I was alone in the boat and at least half the skiiers were on 2 skiis and not that heavy. Took some shaking and wiggling but we did it and ran several hundred yards before one of them fell off. It was fun.<br /><br />Back to the story: Ran like a top and never had any engine related problems. Never saw a stat in it and don't think it had one. Top rear of both water jackets were identical and if it had a stat it should have been there.<br /><br />The guy who bought it wanted to go to a line shack for the weekend down the Intercoastal Canal, shack was some 40 miles away from the launch.<br /><br />He loaded the boat to the hilt with stuff (he later told me) and took off at full throttle to drive the 40 miles. So this translates to 1+ hours of overloaded operation.....had he made it. He didn't, almost did. <br /><br />After he got it back home and to a dealer for repair, he had done just what you said; but because it was overloaded and as people say on here ofter; 2 cycles don't like to be lugged. Now would a stat have made a difference? Who knows. Did it need decarb? I dunno. In those days we never heard of it.<br /><br />Thanks for the input. Enjoyed the opportunity to remember old times.<br /><br />Mark