Go Back  R/C Tech Forums > General Forums > Monster Trucks
Traxxas 2.5 overheating!!!!!!!!!!! >

Traxxas 2.5 overheating!!!!!!!!!!!

Traxxas 2.5 overheating!!!!!!!!!!!

Old 12-07-2008, 08:42 PM
R/C Tech Elite Member
iTrader: (101)
Big Midget's Avatar
Join Date: Jul 2007
Location: Lawrence, Ks
Posts: 4,368
Trader Rating: 101 (100%+)

Originally Posted by kcsoa22

Different store, tech ran 2 tanks of different fuel,(trinity 20%) said ran fine and fast on their track. Suggested new head to insure it stayed cool ($60) I bought it. Got truck home ran 1/3 a tank and stalled overheated. Put new head on and stalled in 5 minutes.
.................................................. ...........................................
Big Midget is offline  
Old 12-07-2008, 10:36 PM
Tech Initiate
iTrader: (6)
Join Date: Oct 2008
Posts: 25
Trader Rating: 6 (100%+)

The likely cause of your problems is that your LSN is very lean, and is causing your overheating problem. The 2.5 is susceptible to this for some reason, i've had the same problem as you're having on all of my 2.5 engines.

Here's what you need to do to tune the 2.5 correctly. I have 3 of these motors and the traxxas default needle settings are way, way off for me.

Set HSN 4 turns out
Set LSN flush to carb barrel, and then add an additional 1.5 turns out.

Set the idle high so that the motor doesn't die out from running too rich at idle.

Run full speed passes and lean the HSN 1/8 turn at a time until you hit peak rpm, and then back off a little. On a 2.5, in California right now, I see appx 250F after doing 7-8 high speed passes, and maybe 10F less on a 2.5r with the blue cooling head.

At this point the HSN is tuned.

Now, lean the LSN by no more than 1/8 turn at a time until you can maintain a steady idle without flaming out, but don't go any further than that. I don't know why, but the 2.5 loves a rich idle, and you will find that you will be rewarded with vastly cooler temps and better performance.

Once you have the LSN tuned, set the idle speed lower until it doesn't engage the clutch at all when idling, and then you'll be all set.

In short, the 2.5 likes the LSN to be as rich as possible, and there is only a very small range (maybe 1/8 of a turn or so), where it won't overheat but also won't stall at idle. Once you find this point, you will likely never, ever have to change it, it is very consistent but very difficult to find.


mud99 is offline  
Old 12-08-2008, 08:30 AM
Tech Initiate
Join Date: Dec 2008
Posts: 43

you definately got some good replies but you gotta know rc guys are like snowflakes none are the same,opinions are like a$$holes everybody has got one you catch my drift well imo it doesnt matter what the temp is as long as you see smoke from the exhaust and your getting good performance and its not cutting out on ya if you can tune like that then drive it no reason to reinvent the wheel rc is a hobby that supposed to be fun not give you a headache although it often can.well i gave you my 2 cents so i hope this helps ya
twayne81 is offline  
Old 12-08-2008, 11:00 AM
Tech Elite
iTrader: (1)
joe of loath's Avatar
Join Date: Mar 2007
Location: Bristol, England, United Kingdom
Posts: 4,857
Trader Rating: 1 (100%+)

I say you should try running a different fuel. Some people say that using other fuels will damage the engine, but that's not so. Sure, it might run a little slower, but it's worth it just to eliminate a variable.

try some of that trinity 20% the dude in the shop used and see how it goes.
joe of loath is offline  
Old 12-08-2008, 10:03 PM
Tech Regular
iTrader: (24)
Join Date: Nov 2007
Posts: 370
Trader Rating: 24 (100%+)

Hey there.
I too have had similar problems...Fuel???? heads???? I don't think so. All was good till about 1.5 gallons.....Then all of a sudden the problem starts. How can that be fuel or head related.....If it was from day one then maybe some kind os issue......But if all was good for some time and now theres a problem, than there is another problem.....Hot means lean.....The fuel is the lubricant not enough fuel means not enough lube....Probably carb related.....You can take it apart....clean it, soak it denatured alcohol...replace the o rings (all of em) and try it again......This is after making sure there are no leaks anywhere...not just the fuel tank but fuel lines,exhaust header.
Good luck .....and
If all else fails........Get a new one
tmaxxdaddy1 is offline  
Old 12-09-2008, 05:23 AM
Tech Lord
iTrader: (21)
Join Date: Jul 2008
Location: Houston, TX
Posts: 11,530
Trader Rating: 21 (100%+)

Both my 2.5s have run hot. When tuned right, they would run 270-295F. Good smoke and good punch and idle. I just didn't like seeing that high of a temp, so I changed head - Nova race pro head. It immediately dropped temps to 250-260F.

Changing to a better cooling head is no solution for a tuning prob, its got to be tuned right and 2.5s require a bit of patience!
Duster_360 is offline  
Old 12-10-2008, 04:28 AM
Tech Rookie
Join Date: Dec 2008
Posts: 7

You guys have all been very helpful. Mud99, The LSN was misadjusted. Took the car out yesterday and tinkered with that... Restored the power that it had when I first got it. But another problem has reared it's ugly head and that is that it won't idle low (it used to be able to maintain a VERY low and VERY stable idle, I could idle through an entire tank. Of course that ended when it started overheating.)

I see that you can soak the carb in denatured alcohol, how about brakleen? What about kerosene or gasoline? The brake isn't powerful enough to keep this thing still now. Idle speed needle has NO EFFECT LSN has little effect HSN- 1/16 turn lean dies when I hit the gas, 1/16 rich dies at idle Should I be looking for a thread about carb maintenance?
nucleartractor is offline  
Old 12-10-2008, 06:46 AM
Tech Initiate
Join Date: Dec 2008
Posts: 43

have you gotten a light weight flywheel because sometimes that will cause an eratic idle if not then it sounds like you must have an airleak somewhere.the carb body is made out of plastic and can wear out creating leaks and undesirable performance which can be replaced for around $16 change your gas lines its about $2 for 3 feet and gas tank repair kit around $5 you can get these things at your local hobby store for these prises.there are more places you can have leaks but these are the cheapest and easiest to start with.get some leak detector from the hardware store and put around your carb while the truck is running making sure you dont get any inside the engine or carb and you can find out if thats your problem.imo i use wd40 to clean alot of my stuff because it cleans,lubricates and it doesnt dry out the o rings.def
dont use gas it eats at plastic.check all your screws on your motor to make sure they are snug(head and backplate)if you could post a vid of it running and driving people could probally help you a little bit more its hard to explain what a motor is doing in words (how it sounds,how it reacts to throttle input etc,etc)hope we can help you figure this out
twayne81 is offline  
Old 12-10-2008, 07:17 AM
Tech Regular
iTrader: (24)
Join Date: Nov 2007
Posts: 370
Trader Rating: 24 (100%+)

Where the actual needle threads onto the carb body is a tricky spot to see any issues. The older ones used an o-ring to seat the needle, The newer one use a plastic "collar" (where the fuel line goes), To tight or to loose could affect your idle. (Be careful) DO NOT OVER TIGHTEN they can crack pretty easy.
Also.....The older it gets (more run time) the less it will idle smoothly.
Bigger heads can't hurt either. The break in process or "heat cycling" is very important as well....With super hot temps.....Metal can "deform" (you would never see it). But you can "pinch" the piston and sleeve to help with this. With all the things you "could" try (unless your set up to do these things) can cost more than a new trx engine If it were a $300 + motor (might be worth it).
Lastly.......IMO...If it runs and smokes and doesn't cut out....RUN IT
tmaxxdaddy1 is offline  
Old 12-10-2008, 01:52 PM
Tech Rookie
Join Date: Dec 2008
Posts: 7

Unfortunately I have no video capability so I cant post a video.
I am using all stock hardware in this engine. Can you tell me more about air leaks and where to find them? I understand that they can lean out the engine and what not. Can you find intake leaks the same way you do on a real car (use an unlit propane torch to sweep across the intake parts until the idle stabilizes.) Also, there is usually some grease around the part where the head and block come together, is this a blown engine (There is not much there, just enough to be noticible.)

Thanks Guys!
nucleartractor is offline  

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.