Running without thermostat

[DWNewt]

I have been running my Johnson 70hp without a themostat in salt and fresh water. I flush the engine with the muffs after use in salt water. Is there any danger in running the engine without the thermostat?<br /><br /><br />Thanks

 

[andy6374]

Re: Running without thermostat

Fouling plugs, quicker carbon buildup, poor idle, and I've heard you can also cause some premature wear to the cylinders (although I don't understand why).<br /><br />I run my engine without t-stats and it does just fine. Although I have to decarb more often. The guy who rebuilt it told me to get as much water through that damm black maxx as possible. He even says to do without the poppet assembly, but I don't understand how that could work.

 

[DWNewt]

Re: Running without thermostat

speaking of carbon buildup, when I removed my sparkplug (fouled out, cylinders 2& 3) inside was kinda crusty black. How do I clean this. Will cleaning these this help the hp?

 

[andy6374]

Re: Running without thermostat

That's carbon buildup alright! Get a can of some OMC engine tuner or Mercury Power Tune. You might need two cans. Get the engine warmed up, then I like to run it at 1500-2000 RPMs. Keep spraying the stuff into the air intakes until is stalls. Remove the plugs and spray some into the cylinders. Let it sit for at least 15 minutes, the longer the better. I like to do mine the night before. When you start it up you will see a cloud of smoke like no other and alot a black crap. Take out for a ride and run the #$$% out of it.

 

[OBJ]

Re: Running without thermostat

Well.....no t-stats may be good for a Max but not John/Rudes. The engines are designed to run at a certain temp for best efficent use of fuel and minimum carboning. I think Tech Man has found this out.<br /><br />Premature wear and even cold siezing can also occur. Cold seizing is when the cylinders do not expand with the pistons. This is caused by the cooling water being to cold around the cylinders. <br /><br />Do yer self a favor Tech Man.....get the t-stats back in it.

 

[andy6374]

Re: Running without thermostat

Cold seizing eh? Cool concept, I would have never thought of that. Obviously if the clyinders don't expand but the pistons do... .<br /><br />Thanks for explanation OBJ.

 

[Joe Reeves]

Re: Running without thermostat

(Thermostat Purpose)<br />(J. Reeves)<br /><br />Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperture to compensate for the distortion.<br /><br />With the thermostat removed, the difference in temperture between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.<br /> <br />The thermostat in your car isn't there simply to have the heater function properly..... think about it.

 

[rodbolt]

Re: Running without thermostat

what Joe says<br /> most all modern pistons are cam ground. that means they are not round at room temps. they are designed to expand round at specific temps. run the hot and they continue to expand until the auto shut off kicks in. that means the skirt siezed to the cyl wall. run them cold and theye were in spots they are not designed th wear in.<br /> ANDY<br /> fix that merc and find a tech that is competent. by removing the tstats you have eliminated water pressure control and are asking for hotspots and piston damage.<br /> dang college grads

 

[Walker]

Re: Running without thermostat

And to add to all that, some OMC have water cooler rectifiers and thermostats at the top of the heads. Take out the thermostat and the circulating water level doesn't reach the rectifier anymore. Results = Fried rectifier

 

[andy6374]

Re: Running without thermostat

Don't mean to keep this in the OMC forum but while we are on the topic:<br /><br />I meant to write that I "ran" w/out tstats, not anymore (they are installed plus poppet). Don't want to knock the guy (the tech), he has a great rep and has always been willing to do the phone conversation thing. A switchbox blew 12 months after I bought the engine from him and he gave me a free used one (I got a free trigger this season). I am just trying to build up the idea that he isn't there to rip ya off. He gave me a written warranty with the motor as well. I've sent plenty of buddies for rebuilds there and their are engines run great. <br /><br />I asked him about the no poppet/tstat thing. He replied by saying never do it to any other motor, but on the 80's V6 black maxx's you "gotta" do it. He said every rebuild (of those particular engines) will last much much longer this way. I'm not promoting the idea just wondering if anyone else heard about this with this era of motors (I guess I have most people's answer)<br /><br />Like I said sorry for stealing the thread as well as it's placing.

 

[DWNewt]

Re: Running without thermostat

Thanks for all the answers guys, I went and got the thermostat. After changing the plugs, cleaning the tank and cleaning out the fuel filter, I started the engine with the muffs. I noticed the difference in the temperature and how much smoother the engine ran after reaching NOT. <br /><br />Thanks,<br /><br />TM