Water temp goes over 180 only in 4th gear

[Dlsnow]

Mci7 8v71 had an overheat situation early in the summer partly due to clogged air filters (mouse trap was sprung - learned alot that day).  So i now know where the bus overheats and shutsdown.  New airfilters now and it is alot  better.

In 3rd i drive all day and water temp sits right at 180.  In 4th (60-65mph) keeping it revved up the temp climbs even on flat expressway.

[Utahclaimjumper]

 YOU THINK??  anytime you climb or go to a higher gear will require more throttle,, more throttle means more fuel,, more fuel equals more HEAT!!  It still should stay under 210 if normal.>>>Dan

[Ed Hackenbruch]

When you say revved up exactly what rpm are you talking about?

[Dlsnow]

Sorry if this is a basic or silly observation
i dont know the rpm...no tach, no speedometer, no fuel gauge...
By revved up i mean to say i am not lugging it.  Everyone says to slam my hand in the door and drive it (8v71) like im mad at it.
Is 210 the line betwren 180 and 250.  It looks a little closer to 180.

I learned that crossing that line on the water temp means the bus will overheat and shutoff.

[bevans6]

My wife and I had a good conversation on this subject today, as we rolled through the hills of Quebec and New Brunswick.  I told her that I had been very worried about overheating on this trip, since I had installed the 400hp 8V-71T engine in my MC-5C with unmodified cooling system - the same as your MC-8 would have had.  We ran 60 - 70 mph up some serious hills and didn't get over 185 degrees.  So it's possible to run cool with these buses.  Anyway, the conversation relevant to your question is - why would adding horsepower make the engine overheat?  Answer - it won't unless you use the horsepower.  More power out equals more heat to disperse, and going to fourth gear and adding speed equals more horsepower out - increased speed just simply requires more power in any gear.  If shifting to 4th gear and keeping the exact same speed as you were in in 3rd gear makes your temp rise, then it comes down to the cooling efficiency of your system at that engine speed.  Higher engine speed means the fans are running faster and moving more air in a stock MCI system, and it also means increased coolant flow through the system, which could also have an effect.

Brian

[lostagain]

Ambient air temperature has a big effect on running coolant temp. I can run any hill at any rpm in cool weather. But when it gets hot outside, like over 90F, I have to back off and down shift to keep it cool. Any cooling radiator, even in the best of condition, will only shed 90 or 100F, I forget the exact figure, so if the ambient temp is say 100F, you are at the limit to keep your coolant below 200F. Running in 100F weather or above separates the healthy cooling systems from the marginal ones.

JC

[gus]

GMC 4107 with 8V71 and Allison V630.

I just completed a 5600 mi trip through some really hot weather, 104+ one day in KC and most days around 100 until I reached ND. My temps were a bit over 180-190 part of the time but I could always cool it back down by slowing down on level ground or using lower gears on inclines. The high humidity is a killer, out west where it was drier I could drive it a bit harder in high temps, but not much.

I found that driving around 60-63 on level ground would keep it pretty close to 180-190 depending on air temps, anything over that made it run hotter but not dangerously so. I ran it a few days in the 68-70 mph area but only in the mornings and usually had to back off after a couple of hours of this to let it cool down.

On the whole trip I never had to add coolant even though I topped the Rockies and Cascades two times each, one pass in the Rockies was appx 7380' and I topped it in early and late August. On earlier trips I had to add gallons of coolant because I hadn't learned to use first gear on the steeper climbs and blew it out the overflow.

Now I shift the Allison down to first gear for these really steep passes which means around 30 mph, slow but cool. It never overheated at any time in first gear no matter how steep the climb. It will overheat pretty fast in third or second because it is too easy to push it too hard in those gears. If I thought it might overheat I stopped for a half hour or so and it cooled right down although I probably never really needed to do that.

I found when reading elevations on my newer GPS that I was very often climbing when it looked level and the engine was slowly getting hotter. Without the GPS this would have been a real concern because I wouldn't have known the reason for the hotter heat reading. I found that GPS elevation readings saved me a lot of fuel, it is practically impossible to accurately judge inclines in the mountains and hills. I though I could easily do this but found out I was way off most of the time!

Once I got out of the mountains it ran around 170 most of the time since the weather was cooler after leaving northeast MT and into ND, MN, WI and IL. Going back south into MO and AR it was much hotter but it stayed around 180-190 with no problems, high humidity too - very high, but no mountains!

WA was wonderfully cool, never any overheating problems there. It was a bit hot in eastern WA but not terribly so even over Stevens Pass. The rest of eastern WA is hot but not very hilly so we never had any problems there either. Two passes in the Rockies on I-90 in MT were the biggest challenges, but first gear made them slow but easy.

[TomC]

Just completed a 600mi round trip in Calif that involved hill climbing (impossible to get out of L.A. without climbing some kind of hill).  With my 8V-71TATAAC (Turbocharged Air To Air After Cooled) engine with 7G75 injectors (375hp & 1125lb/ft torque), I cruise at 1850 which is around 58mph and it stays right at 180 all day.  The thermostats are fully open at 185 degrees.  So once the temp hits 190 degrees on a long grade, I'll turn on the misters.  The temp will creep to 195 and then slowly start coming down to 180 while still pulling the grade.  If for some reason the temp doesn't come down, I always pull over at 200.  The hot buzzer will come on at around 215-have only had that happen once.  Good Luck, TomC