is there any relation between plug temp and outside temp? i have a feeling there is


Active Member
i was bashing with my savage x 4.6 this weekend, and outside temps were about 60f. i am running 30% nitro. i decided to try a brand new mccoy mc9 however the truck didnt really seem to like it. it would sometimes shut off with throttle and it wasnt really reaching temp. so i threw in my traxxas 3232x and the truck seemed to like it better, it reached temps nicetly and seemed to shift into 2nd and had a good amount of smoke and it never shut off again.

i have done research and it seems like there isnt a correlation but i feel like if temps are hot u should use a cold plug and if there mediocre temps then a medium plug and cold temps a hot plug. is this actually factual or not really? i know 60f isnt that warm and it was windy so maybe that was causing the problem,?



Well-Known Member
Glow plug choice is not determined by ambient temperature. You should select the glow plug based on engine size and manufacturers recommendations and nitro fuel content. There is no standard plug temp range so different brands may perform differently.


Well-Known Member
HPISF Supporter
Dekalb, IL 60115
I've always read the same as @lokky suggests. Glow plug temp relates to compression and nitro content. The temp controls the timing of the combustion in the stroke. Too hot and it fires too early and the piston fights itself trying to go up, too cool and it fires too late and blows half the charge out of the pipe before burning it all.

Higher nitro usually runs a cooler plug. Higher compression runs a cooler plug. Typical RTR engines on 20% usually work well with a medium or hot plug. I run 25% nitro and have found that medium temp plugs seem to work the best and give me the best tuning window/performance.


Honestly i look up Factory determined glowplug choice and whatever fuel/Nitro content i use. On top of that there is a personal aspect to IT aswell which is are you going to run it Leaner or Richer. If Richer, i go a little hotter plug then manufactur recommends. And tune from there.
Besides that if its hotter outsider, i use a hotter plug anyway to burn the fuel from the richened tune better and keep engine temp in check.

Imo there is a "rule of thumb" in correlation to ambient temps, if hot ambient use hotter plug to burn fuel more efficient because you don't want to overheat the engine, so you are going to tune it a bit richer.

If cold ambient i use cold plugs and run leaner to keep the engine temps up but don't exceed a max of 290.
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Jacksonville, Fl
Pelican, Olds is right about the plugs. Air temp doesn't determine plug temp. It's based of nitro % and motor size. I'm runnin a slightly modded Axial 28 on 30% (Byron's til they went out of business) and used a cold plug (McCoy MC9) year round.

On a side note, where'd you find McCoy plugs @? I need to get a couple for spares and haven't been able to find them anywhere.


Well-Known Member
Cumberland MD
Hi I would like to hear your thoughts on what I am running and using I am running 20% nitropro fuel and I am going to use a medium hpi plug r4 is what it is I believe I was using a r5 but seemed like my tune was hard to get dialed in I am fairly new to the hobby but understand how to tune just some outside my own head input would be nice thank for any thoughts on this

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