Runs nice and cool one day, hot the next. Why?

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gandalfnz

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Hi Guys

I consider myself to be a good nitro rc tuner. Been doing it for around two years and can make any nitro car run well.
I have finally reached a stage, where I can tune by engine performance and sound, also temp guns I try not to use anymore, and can feel if too hot by touching the cooling head.

One issue has been bothering me for years!

Why does the engine run nice and cool one day, say around 100C and then the next day it goes up towards 130C, which to be hones gets worried a little and then I resort to constantly keep checking with a temp gun to see where its at?

For example. I ran my savage yesterday, it ran excellent, nice and cool, temps never went above 105C, and I thought, thats it, its tuned well, and next time it might only require some small adjustments on the HSN.
Today, I ran it again, and it ran at around 130C. I though this was too hot, and kept richening the HSN, but in the end the car was so rich that performance was clearly affected to the point of being sluggish and taking more time to shift into the second gear.
Point I am trying to make, no matter how much I richen it, it still runs hot! Temp drop is negligible.

Same thing happened with my Revo a while back, took it out the next day and temp was just going up and up!
The weather outside might have changed slightly, but as I said, no matter how rich, it still runs hot!

Is this normal, and should I just forget about the engine temp, it the car is running good?

can't be an air leak, because it would run hot every time I run it.


Thanks
 

gandalfnz

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I am really trying to move away from a temp gun and frequent checks.
But its always at the back of my mind, and when I see it at around 130C, it freaks me out!

Then again, I have seen engines get abused and abused, to the point where they constantly run hot, and even smoke from cooling heat, and they still run good.
And, these are HSP engines I am talking about.

I just like to look after my stuff, which can get a bit obsessive sometimes.

Thanks
 

Bakershaker78

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I am really trying to move away from a temp gun and frequent checks.
But its always at the back of my mind, and when I see it at around 130C, it freaks me out!

Then again, I have seen engines get abused and abused, to the point where they constantly run hot, and even smoke from cooling heat, and they still run good.
And, these are HSP engines I am talking about.

I just like to look after my stuff, which can get a bit obsessive sometimes.

Thanks
Replace your fuel lines, check your exhaust for blockages, and double check that your carb is clean, write down your settings, disassemble, clean, reassemble(put rtv where needed, usually on non moving parts) and put some rtv silicone on the mating surface of the engine, lastly put some rtv silicone on the carb retaining pin and make sure everything is set up as it should be, let it sit for a bit before hooking up the new fuel lines, hook them up, also if you have a fuel filter might wanna check that, either your fuel supply has changed or air is getting in, happy tuning!!!
I am really trying to move away from a temp gun and frequent checks.
But its always at the back of my mind, and when I see it at around 130C, it freaks me out!

Then again, I have seen engines get abused and abused, to the point where they constantly run hot, and even smoke from cooling heat, and they still run good.
And, these are HSP engines I am talking about.

I just like to look after my stuff, which can get a bit obsessive sometimes.

Thanks
Also did you swap glow plugs? If you did you could be getting a cleaner burn resulting in more heat, double check that you are using the same fuel, if you are using a new batch you might need to adjust it a hair, there’s quite a few factors
 

gandalfnz

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Thanks for your help.

Today, it again ran mint. Same weather.
Was even too rich from yesterdays run, so had to lean it.

To be honest, I appreciated all you said that needs doing and I always do this when installing a new engine, but its just too much work to take everything off, clean and then reseal.

No, I didn't swap the glow plug, same one that came with the car.

Will monitor for a while longer, and see if it warrants a strip down.
 

Bakershaker78

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Thanks for your help.

Today, it again ran mint. Same weather.
Was even too rich from yesterdays run, so had to lean it.

To be honest, I appreciated all you said that needs doing and I always do this when installing a new engine, but its just too much work to take everything off, clean and then reseal.

No, I didn't swap the glow plug, same one that came with the car.

Will monitor for a while longer, and see if it warrants a strip down.
Maybe do swap plugs and fuel line, I’m guessing air/burn issues
 

gandalfnz

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Maybe do swap plugs and fuel line, I’m guessing air/burn issues
Forgot to add.
First fix I did was, clean the tank and replace fuel line when I purchased the car.

How would the glow plus have an impact on the temps?

I noticed and that when it runs hot, the cars idle is always higher, obviously the hotter it is, the leaner it gets.
Then I can barely hear the idle fluctuating,
It also doesn't help that HPI themselves specified in the manual that engine temps should not be more than 250F, I find this to be BS, as they almost always run at that temp by default, and even higher.
Dont know in what sort of environmental conditions, HPI tested these cars.
 

Bakershaker78

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Forgot to add.
First fix I did was, clean the tank and replace fuel line when I purchased the car.

How would the glow plus have an impact on the temps?

I noticed and that when it runs hot, the cars idle is always higher, obviously the hotter it is, the leaner it gets.
Then I can barely hear the idle fluctuating,
It also doesn't help that HPI themselves specified in the manual that engine temps should not be more than 250F, I find this to be BS, as they almost always run at that temp by default, and even higher.
Dont know in what sort of environmental conditions, HPI tested these cars.
Hpi engines kinda suck, the glow plug being replaced can result in more consistent runs after because it will hold heat and burn better without a glow starter on it, run it with the glow starter on it, see if it improves
 

gandalfnz

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Having a bit of trouble fine tuning the Savage. Each day it requires a different tune, and idles differently.

See video, after I let go of the WOT, idle is really low and it almost wants to shut off immediately.
Then after I stop, it will shut off after maybe 5 secs or so.
RPM drop, and it has that gargle sound, unsure if its the LSN or it needs wider idle gap, its already at .8mm.
I am thinking its LSN, but it has a really nice take off, and pops wheelies.
Right at the start of the video, you can clearly hear a very low idle, and I have to keep blipping the throttle, so it does not shut off on me.

 

gandalfnz

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I moved up the idle, and now it idles good when tank is full, but when it gets to about 1/3 left, idles is noticeably higher, but will just leave it at that.
It seems this issue cannot be addressed, temps are solid at 110C, will just leave it as is.
 

johnnydmd

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I moved up the idle, and now it idles good when tank is full, but when it gets to about 1/3 left, idles is noticeably higher, but will just leave it at that.
It seems this issue cannot be addressed, temps are solid at 110C, will just leave it as is.

You're always going to run leaner as the tank empties - less fuel pressure. I usually tune with the tank half full.
 

revojoyo

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Hi Guys

I consider myself to be a good nitro rc tuner. Been doing it for around two years and can make any nitro car run well.
I have finally reached a stage, where I can tune by engine performance and sound, also temp guns I try not to use anymore, and can feel if too hot by touching the cooling head.

One issue has been bothering me for years!

Why does the engine run nice and cool one day, say around 100C and then the next day it goes up towards 130C, which to be hones gets worried a little and then I resort to constantly keep checking with a temp gun to see where its at?

For example. I ran my savage yesterday, it ran excellent, nice and cool, temps never went above 105C, and I thought, thats it, its tuned well, and next time it might only require some small adjustments on the HSN.
Today, I ran it again, and it ran at around 130C. I though this was too hot, and kept richening the HSN, but in the end the car was so rich that performance was clearly affected to the point of being sluggish and taking more time to shift into the second gear.
Point I am trying to make, no matter how much I richen it, it still runs hot! Temp drop is negligible.

Same thing happened with my Revo a while back, took it out the next day and temp was just going up and up!
The weather outside might have changed slightly, but as I said, no matter how rich, it still runs hot!

Is this normal, and should I just forget about the engine temp, it the car is running good?

can't be an air leak, because it would run hot every time I run it.


Thanks
Completely the same situation with me. How long are your sessions when you’re running your RC? Also, how old is the engine?
 

gandalfnz

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Completely the same situation with me. How long are your sessions when you’re running your RC? Also, how old is the engine?
The truck has had very little use, I'd say maybe a gallon. Just broken in properly.
I usually run a tank out, so between 20-30 mins per tank.
Also, running in grass will put the temps up a bit too.

How hot is yours running?
Just let it go, make sure it sounds good, has smoke and have fun.
 

tntpoof

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why o people forget the 1 thing with Nitro . it takes constant tuning thru the day whenever you're going to run them
 

gandalfnz

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why o people forget the 1 thing with Nitro . it takes constant tuning thru the day whenever you're going to run them
My original post.

Same weather, same outside temp, yet it runs hotter.
Also, no matter how rich, it still runs hot on some days.
Rich to the point that its not shifting into second.
 

cbaker65

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If the engine sits for too long idling an it just dies ,then the engine is loading up with fuel an chokes
itself out ,the Lsn maybe too rich!
If the engine revs up before it dies ,the Lsn is too lean!

Try to lean the Lsn about a width of a screw driver tip at a time an see if it will idle longer!

Also ,does it it heat up after full WOT or as it sits an idles?..🤔
 
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