Nitro Engine Overheating

[danl]

Hello All,

I'm back into nitro after 30+ years away. I have a Kyosho Inferno MP10 readyset with the .21 Hyper engine. I also picked up a HoBao Hyper SS with the .28 Hyper 6 port engine.

I broke in the .21 and while it gets as hot as 280F on the top of the glow plug I can mostly keep it in the 260F range. I put in a P4 glow plug compared to the P3 it came with stock. I also run it as rich as I can without it choking out when going full throttle.

I got the .28 broken in but I can easily get it above 300F on top of the stock P4 glow plug. Note this is the hottest portion of the engine, other areas are low 200F. It is much more rich than the .21 and blows a solid stream of smoke at mid or full throttle. It will get so hot that it seems to vaporize the fuel in the crankcase and hold a super high choppy idle. I then know it is time to let it idle and cool off. I've gone so far as to bring a handheld fan to cool it off when this happens.

This is all concerning to me as I have it set super rich. I am going to try a P5 glow plug but am not expecting much. I would add some head shims but I think it is something more fundamental. I think my tuning is on as it blows great smoke, accelerates out of a corner well with even more smoke, and holds an idle for more than 30 seconds....easily.

I haver tried trimming the body around the head a lot more. I have also removed the body compleatly. Neither solved the problem. Does it need more break in? I have about 1/2-2/3 gallon through it now.

It is mid 90 degrees here now. I also spend a lot of time full throttle on my makeshift course. It is basically a figure out spread out over 100 feet so that I can practice initiating turns, holding the turn, and coming out of a turn.

My thought is that I am just driving too aggressively for a nitro engine in this weather. But if that were true, then why does my kyosho with a .21 run almost 50 degrees F cooler and I can run it as hard as I wish?

 

[tudordewolf]

If the rest of the engine is in the 200's you might be ok, does the cooling head "sizzle" when flicked with drops of water?

Could it be something external to the engine, like drag in the drivetrain causing it to run under mor load? For that matter, are they geared the same?

A .28 will produce more heat than a .21, but they have about the same crankcase mass & cooling head to get rid of it with.

 

[danl]

Thanks for the input.

The cooling head isn't close to sizzling when I put water on it. It slowly evaporates. The cooling heads are pretty big, so that top fin might not be representative to the temp deep down near the glow plug that I can read 300-320F with my IR temp gun. It just seems "hot" to me, because the idle becomes choppy and it is hard to restart if it stalls.

I cannot find any binding in the drivetrain. The car is new, not that it matters as something could still be off. However when I spin the wheels by hand on the stand, they all move freely. I can get a couple seconds of coast down if I spin a pair of wheels quickly. It is the same as the coast down I get in my Inferno.

The HoBao is heavier than the Inferno. I guess I could swap engines and see if it follows the engine or the chassis.

What I may try next is to only run the HoBao in cooler weather for the next 1/2 gallon of fuel to see if that is enough to loosen it up that it has less friction and thus less heat. It only seems to get hot when I'm really ragging on it. I could probably drive it around all day in 95 degree heat at half throttle.

 

[tudordewolf]

Thanks for the input.

The cooling head isn't close to sizzling when I put water on it. It slowly evaporates. The cooling heads are pretty big, so that top fin might not be representative to the temp deep down near the glow plug that I can read 300-320F with my IR temp gun. It just seems "hot" to me, because the idle becomes choppy and it is hard to restart if it stalls.

I cannot find any binding in the drivetrain. The car is new, not that it matters as something could still be off. However when I spin the wheels by hand on the stand, they all move freely. I can get a couple seconds of coast down if I spin a pair of wheels quickly. It is the same as the coast down I get in my Inferno.

The HoBao is heavier than the Inferno. I guess I could swap engines and see if it follows the engine or the chassis.

What I may try next is to only run the HoBao in cooler weather for the next 1/2 gallon of fuel to see if that is enough to loosen it up that it has less friction and thus less heat. It only seems to get hot when I'm really ragging on it. I could probably drive it around all day in 95 degree heat at half throttle.

If the engine isn't getting too hot it sounds like you're alright, maybe a little fiddling with the low speed needle to tame the idle?

The glow plug wire is incandescent and directly connected to both parts of the glow plug (body and post), so additional heat is constantly being conducted into those components, the plug itself will run a bit higher than the rest of the head.

A P5 plug and head shim might do the trick, if at max revs your ignition is too early, that could be overheating it.

 

[danl]

I'll try a P5 plug and see how that helps. I'll look into finding some head shims as well but I may need to order from HoBao directly which may take more time than just trying out a P5.

 

[easy rider]

On the hyper engine, how’s your idle? How does it drop back to idle after wide open throttle? Idle gap good?

 

[danl]

I set idle gap to 0.5mm. Though I have it 2 hours more gap than that right now. It will idle for 30 seconds easily unless it gets hot at which point it takes on a high choppy idle, as if it’s lean. It’s high enough that it try’s to move the car. If I blip the throttle, the rpm will settle. As long as the engine temp is below 260-280F it returns to an idle fast after a full throttle pull. It seems to perform best at 220-260F.

The high pingy idle is how I know it’s hot. If I change nothing, let it cool to below 260F, it will idle fine. My guess is the fuel is vaporizing in the crankcase and not being burned properly in the combustion chamber. I routed the fuel lines to be away from the exhaust as I thought that was somehow contributing to the issue, but it had no change.

 

[ohsnap]

I set idle gap to 0.5mm. Though I have it 2 hours more gap than that right now.

.5mm seems like too small of a gap, so increasing it like you did makes sense to me.

I am going to try a P5 glow plug but am not expecting much. I would add some head shims but I think it is something more fundamental. I think my tuning is on as it blows great smoke, accelerates out of a corner well with even more smoke, and holds an idle for more than 30 seconds....easily.


It is mid 90 degrees here now

Using OS's grading system - P3, P4, & P5 are Ultra Hot, Super Hot, and Very Hot plugs - made for cooler weather than a 90 degree day.
I would try something like their RP7 cold plug or their RP6 medium heat plugs.
I'm just guessing here, but maybe using too hot of a plug is causing early/pre-detonation and thus affecting the idle.

What is the nitro percentage and oil percentage of the fuel that you are using?

The cooling head isn't close to sizzling when I put water on it. It slowly evaporates. The cooling heads are pretty big, so that top fin might not be representative to the temp deep down near the glow plug that I can read 300-320F with my IR temp gun. It just seems "hot" to me, because the idle becomes choppy and it is hard to restart if it stalls.

With that water test, it sounds like you engine is running cool, except your 300-320 reading points in the other direction.
Confusing.

What is the temperature running at or before mid-tank?
ie - What is it running at the point where you've run it enough to know it's warm?
I shoot for around 220 (mid-point) and usually hit 260-275 at the end of the tank.
While 300 sounds high, if it's just touching that temp at the end of the run, maybe it's the nature of your beast.

 

[danl]

I have a P5 plug arriving Monday. If that moves the temps in the correct direction I will then try the rp6 and rp7.

I’m using sidewinder race 20%, so 12% oil.

I can easily get it over 300 degrees by mid tank. Full throttle 50-75% of the time.

If I drive it easy then I can do a full tank with no issue. I need to keep full throttle down to under 25% of the time and never really allow it to fully rev out.

 

[WRM]

I recently read that P3s are for up to 20% Nitro, P4s for 30%. I've been running P3s in my OS AD3 burning 30% VP Ryan Lutz fuel, so will try the P4 soon. I doubt that glow plug selection affects temperature as much as fuel mixture does. Since you're running 20%, I'd stick with the P3 and richen the mixture to bring temps down? This is written for 1:1, but I found it quite interesting and helpful:

https://www.enginebuildermag.com/2018/01/fuel-mixtures-drag-racing-engines/

 

[ohsnap]

I have a P5 plug arriving Monday. If that moves the temps in the correct direction I will then try the rp6 and rp7.

I wasn't suggesting that a colder plug was going to have much or any impact upon the engine's temperature under normal conditions.

The high pingy idle is how I know it’s hot. If I change nothing, let it cool to below 260F, it will idle fine.

Again, I'm guessing here, but it seems to make some sense to me that a hotter plug in combination with the higher button reading temp on a 90-degree day, could incite a pre-detonation (combustion) condition, thus affecting the idle.


Here's the AI response that I just looked up that kinda aligns with my thoughts.
"The O.S. Engines RP7 is a "cold" heat range glow plug designed specifically for high-performance, on-road RC nitro engines (typically .12 to .21 class) that utilize a Turbo-style head. It ensures optimal performance and prevents pre-ignition in high-RPM, high-temperature environments."

RP7 "Ideal Ambient Temperature Range: 0°C to 35°C (32°F to 95°F). It handles cooler and moderate outside climates beautifully, but provides reliable and consistent ignition even in warm-weather racing."


More from AI...
RP5 Ideal Ambient Temperature Range: "The O.S. RP5 is a "hot" turbo glow plug ideally suited for cool to mild ambient temperatures (typically ranging from 40° F to 70° F). It is designed to provide excellent idle stability and crisp throttle response, making it popular for 1/10th scale off-road, sport engines, and rain tires."

RP4 Ideal Ambient Temperature Range: "The O.S. P4 is a "Super Hot" turbo glow plug ideal for moderate-to-hot ambient temperatures (generally ranging from 65°F to 95°F / 18°C to 35°C+). It helps promote crisp idling and smooth acceleration while accommodating the higher engine temperatures characteristic of warmer summer days."

I recently read that P3s are for up to 20% Nitro, P4s for 30%. I've been running P3s in my OS AD3 burning 30% VP Ryan Lutz fuel, so will try the P4 soon. I doubt that glow plug selection affects temperature as much as fuel mixture does. Since you're running 20%, I'd stick with the P3 and richen the mixture to bring temps down?

RP3 - "The O.S. P3 is an "Ultra Hot" turbo glow plug primarily used for nitro R/C off-road engines (like V-Spec .18-.28 models). Because the P3 is extremely hot, it is highly versatile and performs exceptionally well across a wide range of ambient temperatures (from cool mornings to hot, humid summer days).
While traditional glow plug theory suggests using cooler plugs in hot weather and hotter plugs in cold weather, pro racers and experts like Adam Drake highly recommend using the P3 consistently in all ambient temperatures."


It's a guessing game, isn't it?

 

[easy rider]

Not being a wise guy but, it sounds to me like you have a lean low speed needle.

 

[WRM]

I wasn't suggesting that a colder plug was going to have much or any impact upon the engine's temperature under normal conditions.




Again, I'm guessing here, but it seems to make some sense to me that a hotter plug in combination with the higher button reading temp on a 90-degree day, could incite a pre-detonation (combustion) condition, thus affecting the idle.


Here's the AI response that I just looked up that kinda aligns with my thoughts.
"The O.S. Engines RP7 is a "cold" heat range glow plug designed specifically for high-performance, on-road RC nitro engines (typically .12 to .21 class) that utilize a Turbo-style head. It ensures optimal performance and prevents pre-ignition in high-RPM, high-temperature environments."

RP7 "Ideal Ambient Temperature Range: 0°C to 35°C (32°F to 95°F). It handles cooler and moderate outside climates beautifully, but provides reliable and consistent ignition even in warm-weather racing."


More from AI...
RP5 Ideal Ambient Temperature Range: "The O.S. RP5 is a "hot" turbo glow plug ideally suited for cool to mild ambient temperatures (typically ranging from 40° F to 70° F). It is designed to provide excellent idle stability and crisp throttle response, making it popular for 1/10th scale off-road, sport engines, and rain tires."

RP4 Ideal Ambient Temperature Range: "The O.S. P4 is a "Super Hot" turbo glow plug ideal for moderate-to-hot ambient temperatures (generally ranging from 65°F to 95°F / 18°C to 35°C+). It helps promote crisp idling and smooth acceleration while accommodating the higher engine temperatures characteristic of warmer summer days."

RP3 - "The O.S. P3 is an "Ultra Hot" turbo glow plug primarily used for nitro R/C off-road engines (like V-Spec .18-.28 models). Because the P3 is extremely hot, it is highly versatile and performs exceptionally well across a wide range of ambient temperatures (from cool mornings to hot, humid summer days).
While traditional glow plug theory suggests using cooler plugs in hot weather and hotter plugs in cold weather, pro racers and experts like Adam Drake highly recommend using the P3 consistently in all ambient temperatures."


It's a guessing game, isn't it?

Good stuff - On-Road vs. Off-Road. I've only ran P3s in my AD3s, but will try P4? Did some good practice at the track this morning, think I'll be tuned for the Club Race tomorrow. Burned ~600ml of RL30% w/P3 - took Idle mixture Rich until it "died", then came back one O'clock lean. Nice. Leaned HSN 1 O'clock half way through. Leaned LSN one more "O'Clock" when I got home.

By definition, you must tune your HSN needle/mixture first, then Idle. You want lots of smoke (cooling).