Higher pressure radiator cap?


27 replies to this topic
  • ttr250dude

Posted July 26, 2011 - 04:59 PM

#21

The red one on my bike is a cheapo 8 cell 9.6 volt flat pack battery. Not sure what the mAh rating is, I'm guessing around 1100. My next setup will likely be 1 hobby quality 8.4 volt 7 cell 4200mAh stick pack. 4200 mAh should be way more than enough for a 2 hour race. Here's the one I'll most likely get.
http://www3.towerhob...p?&I=LXAAGJ&P=0

Here's a great place for these batteries. Tower Hobbies almost always has the best prices and more often than not local hobby stores will match their pricing. These are batteries built for expensive hobby quality R/C cars/trucks, these aren't cheapo bottom-shelf-discount batterries by any means.

http://www3.towerhob...wti0093p?&C=CGD

  • twomancrew

Posted July 27, 2011 - 05:29 PM

#22

Posted thread Saturday nite. Sunday morning road High Country Colorado 125miles of gnarly single track :smirk:. 4.5 gallons. Slept. Work. Red eye flight to family on east coast. Sleep. Work. Beach. Check computer and see 40 responses!

Bike ran great on sunday. No over heating. Revloc would not disengage once, I think do to heat.


You are saying a higher radiator cap will cause higher temps but you suggest a catch can to collect boiled coolant. The two scenarios are doing the same thing.
Boiling coolant into a recovery bottle will result in less in the engine thus causing higher engine temps.
I use Evans coolant which has a higher boiling point so it is nearly impossible to loose any coolant which makes the motor run hotter in some cases but if you are aware of that and then all is good. I would rather loose no coolant and not have a higher pressure in the system that's why I chose Evans. It just seems to be the easiest fix and works very well. Never have lost any coolant in some nasty scenarios and never had any engine problems.



Usually run Blue Engine Ice which is supposed to have higher boiling point. Switched to regular antifreeze after symptom started, could not afford boiling $ until I figured out the real problem.



I will check on my actual jetting map. But I will not see bike for a week to check it out. I am thinking of going richer since change from big bore 478 to stock, but there has been no popping on decel. It should pop a little, right?

The fan idea sounds good but our rides are several hours long.

Boiling pressure change with altitude? Hmmm. Is 2.0mb OK then at 10K (plus or minus 2k)? Should I go down to 1.8 or 1.6. Am going to put stock cap back on for a normal ride just to see if my tightening exhaust gasket and tightening hoses solved problem.

The pressure is increased 80%, but how much higher does the temperature get given the altitude? Topped out on Star pass 13k.

Is the temperature or the pressure the bigger problem?

Which is better for my given problem Evans, Engine Ice or Water Wetter?

Still have not put in exhaust gasket, waiting delivery.

  • grayracer513

Posted July 27, 2011 - 09:16 PM

#23

Usually run Blue Engine Ice which is supposed to have higher boiling point.

EI is propylene glycol and purified water at about 50/50, nothing more. You can mix the same thing from ordinary automotive products. Its boiling point at 16 PSI (1.1 bar) is about 280, or ten degrees higher than the standard green ethylene glycol at 50/50.

The fan idea sounds good but our rides are several hours long.

A fairly compact 3000 mA/hr battery will run an 80mm computer case fan for about 10 hours. The fan draws 300 mA.

Boiling pressure change with altitude? Hmmm. Is 2.0mb OK then at 10K (plus or minus 2k)? Should I go down to 1.8 or 1.6.

Boiling temperature changes with altitude. The system pressure is changed as a means of compensating. The difference between 6000 and 10000 feet in terms of atmospheric pressure is about 21 kPa, or .21 bar, or 3 psi.

Here's a chart

Radiator caps are built to hold a certain pressure in the system. What a lot of people don't realize is that there are two forces pushing against the "out" side of the cap; the spring AND atmospheric pressure pressure. Whatever atmospheric happens to be at the moment, the spring will create a pressure difference between the system and the outside air that matches its rated pressure.

But the true pressure on the coolant is the cap pressure plus the atmospheric pressure, so moving from 6000 to 10000 feet lowers the system pressure by about 3 psi. Sea level to 10000 is more like .75 bar, almost 11 pounds.

The pressure is increased 80%, but how much higher does the temperature get given the altitude?

The temperature doesn't increase, or even change much. The boiling point varies by pressure. A 50/50 PG/water mix boils at ~235-240 ℉ at sea level in open air. With a 16 pound cap, it's ~280 ℉. To maintain that at 10000 feet with the 11 pound loss in pressure, you'd need a 27 pound cap.

Is the temperature or the pressure the bigger problem?

Pressure is only a problem in terms of containing it. Temperature is what damages engines. Boiling is the worst. Not boiling at a high temp is better than boiling at a low temp because boiling coolant does not cool the engine parts that are the source of the heat, and the real heat of those parts runs away uncontrolled.

Which is better for my given problem Evans, Engine Ice or Water Wetter?

My preference is to control the heat at a reasonable boiling point. If that can't done, next thing is to raise the boiling point. The biggest concern is to retain as much coolant as possible and prevent it from boiling.

Still have not put in exhaust gasket, waiting delivery.

The exhaust gasket will not contribute to overheating in any way.

  • ttr250dude

Posted July 28, 2011 - 01:08 PM

#24

It should pop a little, right?


From the answers of professionals i've found, yes. A little pop is good.


The fan idea sounds good but our rides are several hours long.


It all depends on how many mA the fans uses. The amount of mA depends on how much air said fan will flow. If you wanna go crazy you could get a 140cfm fan and an 8000mAh LiPo battery and it'll run forever, but i dont see that ever being neccesary..

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • FinchFan194

Posted August 23, 2011 - 12:26 PM

#25

Gray, can a lean situation cause him problems also...low or high altitude?

  • upnorthbacon

Posted August 23, 2011 - 12:36 PM

#26

Here's what the CRF guys did, but it runs off thier battery. Might have to put a small battery in the airbox?

http://www.thumperta...ad.php?t=941846

  • grayracer513

Posted August 23, 2011 - 01:17 PM

#27

Gray, can a lean situation cause him problems also...low or high altitude?

Probably not. For one thing, 4 strokes are very tolerant of jetting outside the optimum either way, and just aren't very prone to heating up from being lean. The engine would start running really badly before problematic heat resulted from it.

Secondly, increased altitude typically leads to an engine that is too rich.

Another effect of altitude we haven't touched on is the reduction in dynamic compression. The compression ratio, of course, does not change, but the lower air density reduces the peak compressive pressure produced before ignition. It can sometimes actually be beneficial to switch to regular grade (87 pump octane) gas at around 6000 feet.

  • FinchFan194

Posted August 23, 2011 - 01:18 PM

#28

Interesting.





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