Tmaxx 2.5 overheats

[bhershey]

I bought a Tmaxx 2.5 about 2 weeks ago and broke it in according to the instructions. Recently I bought an onboard temp gauge to make sure I'm not running too hot. This past weekend I ran it with the HSN at 4 turns from closed and with the LSN flush and it was getting up to 280-300 when I'd do 2 or 3 WOT runs. This was in north Louisiana and the temps were 90-96 F. I'm really new to this game, but I think it's idling normally. Anyway, don't know if it could be an air leak. I've read that leaks can cause you to run on the lean side. Should it be running at 220-260 during WOT? I don't want to keep running it this hot for fear of killing the engine so quickly. Can anyone offer suggestions to rule out possible causes for this?

Thanks,
Brad in Dallas

 

[Thrashman]

I'm a complete newbie to all this....can you tell me what WOT means? Thanks

 

[dougc]

wide open throttle, Meaning you had your car maxed out on RPMS for a few seconds

 

[Plaidfish]

bhershey, first off the needle settings you gave will really mean little to anyone but your self.....if your engine runs hot then you need ot richen the mixture on your HSN (high Speed Needle) first....don't hear someone in Nor. Cal say he sets his to xxx and expect your car to perform the way his did....you need to be able to tune the engine yourself or this hobby will drive you freaking nuts.....that being said richen your HSN about 1/8 of a turn and see what temps you get after doing a few WOT passes...2 ro 3 pases AFTER you get the engine up to running temp......after you run your engine EVERY time, make sure your piston is at BDC (bottom dead center) so it won't cool off and stay wedged in the sleeve....do a search on this forum for engine tuning and read (yes there is a lot) all that stuff.....the more you know the fewer engines you'll blow

 

[olds97_lss]

Also... since rolex isn't around as much anymore, I'll tell you to get a ACNCM head for the 2.5. After which, re-tune for performance while getting a nice stream of smoke coming out of the exhaust when your on the gas.

ACNCM Short for 2.5
ACNCM Large for 2.5

 

[Pig]

A new head will help you out quite a bit. Just be sure you reuse your head shim. The shim is the very thin washer between the head and the mill. Do a search on here and read up on it if your not sure about things.

Richening (or enriching for Bill) will lower the temps, however, when you move beyond the point of performance degradation it will actually reduce your engine life slightly. You have to play a balancing act to be slightly on the rich side of best engine performance.

Lastly, northern Loo-zee-anna is pretty darn humid, add to that temps in the mid 90's and your engine will run hotter than normal. This is where a newer head will help you out. Also, if you're bashing, make sure you have plenty of ventilation in the body. If you're racing, ventilate the body to the maximum your track allows.

 

[chewyboy]

also look at this thread for proper tuning

https://www.rcnitrotalk.com/forum/showthread.php?t=32563

scroll down i redid the flowchart in visio, if you dont have that, i also attatched a jpg of it that hopefully is a little bit clearer than the first post.

 

[bhershey]

Continued difficulties

Thanks for your help. I took the truck out yesterday (I'm back in my hometown of Dallas, TX) and played with it a bit. I just replaced the carb body because I had stripped out the HSN plug. Anyway, the seals are all new and I did the following:

1. made sure HSN was set to factory settings (4 turns out from closed)
2. made sure the LSN was flush with the carb slide
3. made sure the idle was set such that there was about a 1mm gap in the carb

I ran it a bit and leaned down the HSN a bit until the performance increased. I messed with the LSN and idle so that it idled low but without dying. I also changed the LSN so that the car died in 3 seconds using the pinch test. THen I ran about a tank of fuel through it. WHen I first started running after tuning it, it was good and the temp stayed below 270F. I also took the air filter off BRIEFLY and put my finger over the nozzle and the truck died INSTANTLY. I put the filter back on and ran it for about 5-10 minutes and brought it in and noticed that the idle was increasing and varying. The temp then started to increase and I had to shut off the engine so it wouldn't go too high. Any ideas what could cause this? THis was at about 8:30pm and the local temp was around 80-85F.

Thanks,
Brad

 

[Revo Rancher]

Double check your Rx batts. If they are low the T-Maxx servo for the throttle tends to hunt, causing the throttle to twitch slowly. Does not sound like an air leak as it died right away when you covered the carb.

 

[bhershey]

That's true Revo, but I am thinking I should try that when the model's idle is varying. Perhaps the engine has to heat up, then the leak manifests. What do you think?

 

[Revo Rancher]

At the carb try your air test with the filter off (Clean environment) after your engine is warm and is starting to have the idle vary up and down. If you get the same results, i.e. it shuts down right away, then it most likely is not an airleak. Doesn't hurt to seal the carb and backplate anyhow.

Also, turn on the Tx and Rx (motor not running) and after a few minutes see if you can see the servo twitching or moving ever so slightly. If it is, charge the Rx fully and try again. If that does not stop the throttle servo from twitching, then I give up!

 

[rbmaxxbasher]

Try going with a receiver pack for your radio. It's five cells and it hold more stable power for your receiver.

 

[bhershey]

Revo,

I don't believe that it's a problem with the radio system. What carburetor/engine issues could cause a varying idle speed? I know that the textbook answer to that is an air leak. I pulled the fuel tank and tested it for leaks and it looks good. I also tested the fuel line and the overflow line. There was a bit of fine sand in the fuel tank but not a lot. I obvioulsly cleaned it out.

I had run the truck at a constuction site and there was a pile of fine sand that I was jumping. Anyway, there seems to be that sand all over the truck. I had the air filter on the whole time I ran it, but it seems a bit of sand got in the fuel tank. I should buy a fuel filter.... anyway, should I break down the engine just to be sure there are no corrosive sand particles in there? If so, what is the best way to do that?


Thanks,
Brad

 

[4u2nv]

Try going with a receiver pack for your radio. It's five cells and it hold more stable power for your receiver.

lol.. Are you serious?? Over heating from his controller batteries?? :spit:

 

[Shocker]

Airleak

It sounds like you probably have an airleak somewhere. I had 2 airleaks on my 2.5R...

The first was the carb, I had to remove it (loosen the hex nut and gently slide off) and seal it with "Oxygen Sensor Safe High Temp RTV Silicone Seal". It's the stuff in the Copper tube. Make sure you get that one specifically. Just place a thin coat around the bottom and slide it back on. Let it dry for about 24 hours and your safely sealed up!!!!

Now I don't know :shrug: if the T-Maxx uses the same gas tank and seal as the Revo, but if it does....

The most common problem on the Revo is the little blue O-Ring in the gas tank lid giving out. Check you lid, if it no longer "pops" into place, the O-ring has probably stopped sealing. This is the one HUGE flaw in the tank design. The worst part is that to replace it you have to buy the $6 rebuild kit that includes all the tank lid parts when all you need is the O-ring.

 

[tbbh-teacher]

surerly you can find an oring at a parts store. Measure the diameter and thickness and google it see what you come up with. I know on AM radios the interference is sick so twitching servos could cause it to idle up and down. As was said by others

 

[Plaidfish]

measure the O-ring and go to McMaster Carr....if they don't have it no-one will.....

 

[bhershey]

A quick update to my issue:

I took the truck to Traxxas (I live 15 minutes from their hq) and they looked at it. They replaced the piston and sleeve and said it was worn out. I talked to someone at my LHS and he said that's all Traxxas will do if you send them your truck: replace the piston and sleeve, and they won't tell you the results of any testing they did and/or what was found wrong. Anyway, I broke it in and it was still overheating afterwards. Then I bought an ACNC giant cooling head. That seemed to do the trick. Also, I had to richen the LSN a half turn or more from the factory settings to get it to keep from overheating. It seems that the factory setting (flush against the LSN assembly) is too lean for my truck. Anyway, I richened it and it has a lot of punch off the line and runs around 235-245. That ACNC head is huge but sure helps out!!! It makes the stock head look anemic and tiny. Anyway, thanks for your suggestions. It seems that the often repeated wisdom holds true for me: Absolute needle settings don't have a lot of meaning for effective tuning of a nitro engine.

Brad