How Hot is TOO HOT

[rcguy76]

Ok...I have heard and all in general followed the run of boiling water on the head of a nitro engine meant it was running to hot...so 200 Degree +/-

After reading a article on reading a glow plug , I'm somewhat confused..I am currently running the new K&B .45 outboard and this spring a O.S. .21 inboard. This past summer I ran the 45 and tuned the engine to run around 200. I read the article about reading the glow plug ,so I leaned out the engine until it slightly browned the plug and its running great...although water does boil off the head. So my question is whats is the proper running temps for 45's and 21's....I really dont want to ruin the 45....I had to wait 7 months to get it last year.

Thanks for any help you all can be

Chris

 

[BradV]

Sounds too hot to me. If I can't hold my thumb on top of my motor for 3 secs then I count mine as running too hot/lean. A water sizzle then definately too hot by my standards.

Tuning is an art and you can write heaps about it, but my method is to get the mixture set so you get the best possible boat speed on the straight aways at WOT (providing prop etc is optimum), then go a notch or two on the rich to compensate for the turns and to make sure you don't run too lean with longer periods of running. I'm also used to the sound/pitch so I can generally tell if my motor needs a little more or less fuel.

You can also get used to reading the amount of smoke that exhausts, but outboards not so easy to tell. If you get no or hardly any smoke from your motor generally a sign of too lean.

After I do the above I then check the plug as a secondary sign of mixture and detonation, and not as the primary method as you seem to indicate. My glow plugs only brown off slightly on the first coil with nitro above 20%, otherwise they stay pretty shiny until they get a bit old.

 

[Allen Waddle]

I believe this 200 degrees you are being told about is dealing with air cooled engines generally in rc cars and trucks. Alot of publications dealing with cars and trucks use this # and is pretty safe in most engines stock configurations with non aftermarket air heads. i add this because I run cars quite abit and boats more than that. I have on offroad 1/8 scale buggy with an aftermarket head that if you were to run at 200 degrees would be toast in a matter of minutes however I have an 1/10 scale on road car that likes 300 degrees. This 200 Degree number is probably a safe # for most on cars and trucks but is not an optimum number for many cars or trucks. I assume they print this for those that due not now how to tune there engines.

I dont believe that you will have a lot of success finding a NUMBER THAT WILL WORK WELL FOR BOATS DUE TO THE FACT THAT MOST ARE WATER COOLED. The only time I have ever used a temp gauge on boats is when trying to tune twins,not all that usefull for that either. However i will say that a particullar set of cmb 80's I have like to be run at the 130 degree range. Keep in mind that it is almost impossible to get a real reading on marine motors because they are water cooled and when you throttle down to bring boat to shore the cool of considerably even for that short period of time. the reading of 130 that i speak of is coming in at our practice pond as fast as is safe and taking readings at plugs before boat is lifted out of water.

Hope this helps.

Sincerelly,

Allen Waddle

 

[Don Ferrette]

Ok...I have heard and all in general followed the run of boiling water on the head of a nitro engine meant it was running to hot...so 200 Degree +/- After reading a article on reading a glow plug , I'm somewhat confused..I am currently running the new K&B .45 outboard and this spring a O.S. .21 inboard. This past summer I ran the 45 and tuned the engine to run around 200. I read the article about reading the glow plug ,so I leaned out the engine until it slightly browned the plug and its running great...although water does boil off the head. So my question is whats is the proper running temps for 45's and 21's....I really dont want to ruin the 45....I had to wait 7 months to get it last year.

Thanks for any help you all can be

Chris

Chris-

Reading the plug will tell more about how it's running than anything else. If the plug comes back looking like it should & it's running like you want it to sounds like you're on the mark. Keep it mind that when you bring a boat in the temp will actually rise as the flow of water has stopped but the engine itself is still retaining significant heat from running. My personal "quick check" is if I can hold my finger on the head longer than about a second to a second & a half it's running cold. Pop the head button & look at the combustion chamber & top of piston. If it's not detonating & giving the piston & head button that sandblasted look then I say let 'er rip! B)

 

[rcguy76]

Thanks for all the replies...the K & B pro is the air cooled version. I emailed K & B tech about converting it to Water cooled and they gave me a list of parts with about 100 bucks worth of parts to convert it to water cooled........so I think I'll look into exactly what I need alitle more..but the OS is water cooled..so I should be able to play with that alittle leaner

 

[Scott Schneider]

<_< Unlike a lot of you folks I watch and set my operation temputure on crankcase and mid engine temp. The head/water jacket will typically read as cooler that the bulk case mass of the engine.

We get maximum effiency and atomization of the fuel mix when we heat it up to the @ 160 to 200 degree mark.

These nitro engine are "AUTO" ignition and there firing point to ignite the mix is based on tempiture and pressure.

My personal observations have been if I first manage my engine case temp where i want it ( and yes head temps are HOT! ) and adjust compression acordingly to keep detonation under controll i get more power over a wider operation range than i would setting head temp only and having a generally cooler engine case.

So in reality i am running my head temps easyly at or over 200 degrees.

But remember this: so long as engine is getting water and transfering that heat into the passing water, The water will not boil because it never gets to temp the engine is running at, Its not there long enough and its job is to only be a heat sink.

To be able to ballance this from lake to lake and season my rudder pick up, hoses, engine fittings are all as large as possable. Then I use a small valve (Drip irrigation)

type to regulate the flow as needed. If possable on the discharge side of water jacket to maintain high system pressure in the water jacket. :unsure: Scott

 

[izitbrokeyet?]

I'm with Scott regarding the higher temps. I do check head temps when I can get a "quick" recovery and I look for 230 on a .21 motor. I look for less on a larger motor, but I generally find that motors run harder and seem to last longer at higher temps. I try to get close to combustion chamber temps by shooting right next to the plug (not always possible) I treat buggies and boats similarly whereas I check temps and make sure there’s no signs of pre-det. I set my shims to shim for a target temperature of 230 on boats and 200 on buggies.

 

[BradV]

Well I might have to run mine a bit hotter and see if I get any gains..