Nitro Engine Cooling

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Al Hobbs

Legend of the NW
Vendor
Joined
Aug 25, 2009
Messages
1,956
Most of us on I.W. have been running model boats for quite a while. But there are plenty of inexperienced boaters as well.
Properly cooling your engine is a good subject to discuss for new boaters.

Back when I got started we made our own rudders, silver soldering a steel blade to a steel post. We used a brass tube to scoop water behind the prop and then used a silicone tube to take water from the scoop to the engine water-cooled head. A water fitting carried the cooling water from the engine to outside the hull. From the shore, we could see water squirting out of this fitting to make sure our engine was cooled.

An enterprising person came up with an aluminum, wedge shaped rudder with a built in water scoop. Almost everyone today is using a rudder with the built in water scoop. Water is directed from the rudder to the engine's water jacket.

Your engine builds heat by burning fuel. It creates a lot of heat. The heat is created between the head button and piston face. This is the hottest area in the engine. If this area gets too hot, engine performance drops and sometimes the piston is ruined.

Most of the heat generated escapes through the exhaust. But, the area between the head button and piston face still need cooling. The crankcase does not get overheated as it is removed from the combustion area and cooling fuel is directed into the crankcase. The area you need to cool is the upper end of the engine. Most engines have either air cooling fins or a water jacket around the head button.

The water scoop will send more water to the water jacket than is necessary. The brass water fittings will allow more water into the water jacket than is necessary. As a result, many new boaters over cool their engines.

Our engines need heat to burn nitro fuel The higher the nitro content, the more heat is needed. If your engine is too cool, it will not burn all of the nitro. That is when expensive nitro is wasted, going out with the exhaust.

To prevent your engine from becoming overcooled you can restrict the water flow. Experienced model boaters use different methods to restrict water flow. Some use a small plastic tie-wrap on the silicone water line. The tighter the wrap, the less water gets to the water jacket. Some use a needle valve in the silicone water line to adjust water flow. Some remove one brass water jacket fitting, seal the hole off with a set screw, then drill a small hole in the water jacket top to allow water to flow at a reduced rate.

This leads to the questions, how cool is too cool? And, how hot is too hot? Some boaters actually use a heat gun to monitor the engine heat, adjusting the water needle valve to get the exact temperature they want. I feel the water jacket when my boats come back in. The water jacket should be cool enough for me to hold without burning myself, but hot enough that I can't hold it more than several seconds.

The engines we buy, produced in Europe, are designed for a lot more cooling than we need in North America and Australia. This is to suit the European market. Their most popular classes are 30 minute endurance events with a completely cowled engine and pipe. In this instance, the engine needs much more cooling. Our 3 to 4 minute races, even with a cowled engine, do not produce as much heat as in the European endurance races.

Check your water jacket temperatures often as the water we run in can change temperature during the days you are running.
 
Most of us on I.W. have been running model boats for quite a while. But there are plenty of inexperienced boaters as well.
Properly cooling your engine is a good subject to discuss for new boaters.

Back when I got started we made our own rudders, silver soldering a steel blade to a steel post. We used a brass tube to scoop water behind the prop and then used a silicone tube to take water from the scoop to the engine water-cooled head. A water fitting carried the cooling water from the engine to outside the hull. From the shore, we could see water squirting out of this fitting to make sure our engine was cooled.

An enterprising person came up with an aluminum, wedge shaped rudder with a built in water scoop. Almost everyone today is using a rudder with the built in water scoop. Water is directed from the rudder to the engine's water jacket.

Your engine builds heat by burning fuel. It creates a lot of heat. The heat is created between the head button and piston face. This is the hottest area in the engine. If this area gets too hot, engine performance drops and sometimes the piston is ruined.

Most of the heat generated escapes through the exhaust. But, the area between the head button and piston face still need cooling. The crankcase does not get overheated as it is removed from the combustion area and cooling fuel is directed into the crankcase. The area you need to cool is the upper end of the engine. Most engines have either air cooling fins or a water jacket around the head button.

The water scoop will send more water to the water jacket than is necessary. The brass water fittings will allow more water into the water jacket than is necessary. As a result, many new boaters over cool their engines.

Our engines need heat to burn nitro fuel The higher the nitro content, the more heat is needed. If your engine is too cool, it will not burn all of the nitro. That is when expensive nitro is wasted, going out with the exhaust.

To prevent your engine from becoming overcooled you can restrict the water flow. Experienced model boaters use different methods to restrict water flow. Some use a small plastic tie-wrap on the silicone water line. The tighter the wrap, the less water gets to the water jacket. Some use a needle valve in the silicone water line to adjust water flow. Some remove one brass water jacket fitting, seal the hole off with a set screw, then drill a small hole in the water jacket top to allow water to flow at a reduced rate.

This leads to the questions, how cool is too cool? And, how hot is too hot? Some boaters actually use a heat gun to monitor the engine heat, adjusting the water needle valve to get the exact temperature they want. I feel the water jacket when my boats come back in. The water jacket should be cool enough for me to hold without burning myself, but hot enough that I can't hold it more than several seconds.

The engines we buy, produced in Europe, are designed for a lot more cooling than we need in North America and Australia. This is to suit the European market. Their most popular classes are 30 minute endurance events with a completely cowled engine and pipe. In this instance, the engine needs much more cooling. Our 3 to 4 minute races, even with a cowled engine, do not produce as much heat as in the European endurance races.

Check your water jacket temperatures often as the water we run in can change temperature during the days you are running.
Great explanation. Very good information. Being new to this hobby, I started last year with one boat and now have 3, I feel this is directed towards me and I deeply appreciate your time and efforts in explaining this enigma. One question I have is this, is there a target temperature I should be looking for? I have an O.S. Max .46 VR-M and a Picco competition 90. As usual, your reply and valued knowledge is greatly appreciated.
Greg
 
One mistake I have seen people make is positioning of the cooling ring on the block.
Especially with Picco’s … there is a transfer slot in the block between the lower and upper portion of the block. I’ve seen people line up the inlet of the cooling ring with that slot.
Water follows the path of least resistance and
water entering the ring will transfer straight up into the head and the lower part of the block doesn’t get cooled properly as the ring is essentially deadheaded… will it fill with water?
Absolutely, but it has nowhere to go.

The inlet needs to be as close as 180° to the transfer slot so the water flows around the cylinder and then up through the transfer port to the head and then discharged…

Also some cooling heads have a baffle in them to assure that water flows all the way around the head.. and may need to line up on the block to properly cool. Pay attention to the small details.

On a twin, if you split the water with a tee or Y
It’s important to keep all the water lines, nipple sizes discharge holes in the head the same length and size… again water takes the path of least resistance and one engine may get starved for water..

One more thing worth mentioning is the inlet on the rudder blade, I personally slot the edge of my rudder blade at the water inlet with a round file,

I’ve seen riggers stop watering when a small bit of left rudder is applied for course correction, the sharp edge of the blade cavitates and water bypasses the pickup hole in the blade, and watering stops…

just a few tricks I’ve done over the years to my boats… again it’s the small things..

YMMV…. 😁👍
 
Oh, and not all engines need the water restricted… anyone that has run an OPS .67 or .80 on 50% can attest to this… I don’t think there’s any way to “overcool” one of these motors… 🤣🤣🤣
 
Great explanation. Very good information. Being new to this hobby, I started last year with one boat and now have 3, I feel this is directed towards me and I deeply appreciate your time and efforts in explaining this enigma. One question I have is this, is there a target temperature I should be looking for? I have an O.S. Max .46 VR-M and a Picco competition 90. As usual, your reply and valued knowledge is greatly appreciated.
Greg
There is no target temperature for everyone. It depends on your fuel, engine, hull, etc. When you are testing and the boat is runing very well, take the temperature with a temperature gun. That will give you a target temperature where ever you are running.
 
Brass head buttons help stabilize the transfer of heat. Thy act as a heat sink and do not fluctuate as much as aluminum. This makes for a easier time tuning the eng.
Also replacing the cap that holds down the head and reducing the water chamber helps reduce the water contacted to the head and removing water from the top of the case.
The case dose not need water colling only the top of the button.
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Brass and reduced water jacket volume work well in cold water conditions. They will retain more heat than aluminum head buttons and larger water volume jackets. However, brass does not transfer heat as quickly as aluminum. In warm or hot water conditions, you need faster temperature transfer. If you cannot transfer the heat as fast as you need it transferred, the piston can be damaged.
 
Brass and reduced water jacket volume work well in cold water conditions. They will retain more heat than aluminum head buttons and larger water volume jackets. However, brass does not transfer heat as quickly as aluminum. In warm or hot water conditions, you need faster temperature transfer. If you cannot transfer the heat as fast as you need it transferred, the piston can be damaged.
Worked pretty good for me in Florida.
 


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