Overheat solution for MCI 8

[billngayle]

I have a severe overheat problem with my MCI8 and have a possible cure, just wondering if anyone has tried using the internal heater core as an aux radiator.  It is huge and my thought is to cut a couple holes in the floor in front and mount automotive radiator fans to blow air below the bus.

[bevans6]

The feed to and from the heater core is quite small, 1" tube, so it will not flow much coolant.  There is no realistic place for the small automotive fans to draw air from, except the front luggage bay or cutting a big hole in the old AC condensor bay (I assume you have ditched the ATR stock AC if you are thinking of re-purposing the heater core). If you have a normal engine for that bus (8V71N) I would personally fix the actual problem and look towards the radiators needing repair, the shutters closing, the fan dampers closing, thermostats, measure the coolant system pressure to make sure the pressure bypass is working, or trying the old "open the engine bay doors" trick.  If you have an uprated engine, then I would consider adding a second radiator mounted underneath the passenger side radiator in the engine bay, where the AC compressor used to be or beside it, blowing down through the floor, plumbed in parallel with the passenger side radiator (yeah, I have thought about this, I have plans to do that in my bus if I need to).  You can access the coolant plumbing easily for this - tee into the top pipe going up from the thermostat housing as the input, and tee into the lower pipe along the engine cradle that runs to the bottom of the water pump as the output.  Or bite the bullet and upgrade to the MC-9 radiators designed to cool the 6V92.

The reason I think of fixing the actual problem is that the cooling is adequate for the normal engine heat output if it's in good shape, so you really shouldn't have a severe problem if the radiators are sound.  And if the radiators aren't sound, putting a band-aid on isn't a long term solution.

Hope these ideas help,

Brian

[robertglines1]

Your thinking! that's good. have you tried turning heat on going down road and see if it makes difference?  biggest problem with 8's is seals around rad getting bad and letting air around rad instead of thru. Foam in a can --- can help seal those areas. also ck to make sure the air horns( tapers inside) your fans are still there and are in good shape. Might be a good time to revisit this subject for benefit of new guys.  Also try search function on blue bar above.      It's a common problem with many solutions!  only dumb question is the one not ask! Bob

[lostagain]

Welcome billngayle,

your engine, (8V71 ?), should not be overheating.

Have you looked at the rads? No air should be able to go around them. Make sure any space around them is sealed properly. You can use expanding foam. Make sure the doors to the rads seal well too. All the air blown by the fans has to go through the rads, not around them. Make sure the squirrel cage fans are clean. One big hole often is where the fan belt goes through into the fan compartment. I used a piece of rubber belting to plug mine up with just two small little square holes for the belt, to replace the torn up old one.

Another possible cause of overheating is not revving the engine fast enough. Down shift it so you are driving it on the governor. Do not lug it.

This will get you started.

Other knowledgeable nuts will post soon with other ideas.

JC  

PS: see, 2 other nuts have already answered while I was typing.

[buswarrior]

As noted Seals, seals seals seals.

We cannot overemphasize that even what you might think is a small leak past the doors or around the rads instead of thru them is a game ender.

But if the rads are rotten, you'll be wasting your time, because all that stuff has to be removed again to change the rads.

And, same as an auto, once the rad is rotten, it doesn't cool. Period, full stop.

Expending time and money on band-aids just sucks resources away from the myriad of other things we have to do to get these things converted and maintained.

Would you describe the weather and driving conditions you are experiencing overheating?

happy coaching!
buswarrior

[luvrbus]

Good info the guys are giving so here is my take people never change the seals in the thermostat housing a 8v71 will heat in a hurry if the thermostat seals are bad and you will always go back there so why not start there  JMO

Check the water pump also the nut backs off the shaft letting the impeller turn on the shaft,a bad muffler and tail pipe will cause it to heat  plenty of things can cause one to heat   

good luck

[billngayle]

Some additional information on my situation:
We swapped out the 8v71 for a 8v71 turbo which is probably adding some additional heat.  During the swap I had the radiators thoroughly cleaned and rodded sop they should be working as well as they can.  The seals around them appear to be in good shape and minimal leakage.  The overheating is occuring in western Colorado on hot days.  The piping to the heater core is 2", same as the rest of the radiator pluming so the water flow should be adequate. 
Thanks for all the suggestions and will look into them to see if anything helps.

[lostagain]

Yes, an 8V71T will put out more heat than an N. How big are your injectors? MC9 rads are taller, requiring some surgery to your bus to install them.

Another thing you could do if not done already, is install a smaller pulley (8" IIRC) to spin the squirrel cages faster. The stock pulley is like 12" IIRC.

Is there a rubber skirt hanging off the rear bumper? That would hinder hot air flow out of the engine compartment. Some of us have a rubber flap hanging in front of the engine between the mud flaps to (in theory) create a vacuum to draw more air out toward the ground.

And, repeating myself, really make a point of running as close to the governor as possible going up a hill. That may mean 2nd or 1st gear on some steeper hills. You will heat up real fast lugging it at anything less than 2000 rpm. Please ignore this comment if you are an experienced driver and know this already.

JC

[TomC]

I turbo'd and air to air intercooled my 8V-71.  I also had my radiator (standard side radiator) increased to a 6 row with serpentine fins.  It is the largest that will fit.  I augment my cooling with misters (have no choice).  At first I used 15 misters from Home Depot-they worked fairly well, but could still overheat.  I then drilled out two of the lowest ones to 1/16" and now it will pull down the heat.

With a 8V-71, if you converted to a turbo and don't have either the aftercooler (which doesn't look like since you didn't say it is a TA) or run an air to air intercooler, your injectors should be no bigger then 75's-that will get you 350hp and 1050lb/ft torque.  If you have an aftercooler of some sort, Detroits largest from the factory were 80 injectors for 400hp and 1200lb/ft torque.  Take a look under one of the valve covers to see what you're running.  Good Luck, TomC

[billngayle]

My injectors are 75's.  I had misters previously, 2 on each side and removed them due to they didn't appear to be of much help and was told that the water spraying on the radiators was not good for them due to the minerals in the water leaving deposits.  I could see where 15 would maybe help, could you perhaps upload a picture of what you have?  Also, I do not have any of the little radiator doors that controlled the temperature, all that has been removed.

[Lin]

Of course, as mentioned make sure there are no leaks for air to get by the radiator.  There are some other ways to increase air flow.  Also mentioned was installing a smaller pulley to get greater fan speed.  Many say that installing an air dam, basically a mud flap that runs all the way across the bottom just behind the rear wheels helps a lot.  I have done that an think it does.  If you have a mud flap in the back around the rear bumper, remove it.  The mud flap in the wrong place decreases air flow.  Another thing that I thought helped was rigging a jig that holds the rear engine doors open.  That also increases air flow by lowering resistance.  Scoops are controversial.  Some say that don't do anything.  Others say if built right, as described on Fred Hobbie's website, they work well.  I gave my screens to a sheet metal shop just before the summer to get some made, but he still only has them half done, so those will not be tested until next year.  However the good news is, I did not have any hear problems this summer.  The mudflap and the open doors seem to help.

Another thing though that needs to be watched is your rpms.  My 8v71 is said to be most efficient between 1600 and 1800.  In past years, I thought it was best to rev the engine higher when climbing hills to get the fan speed up.  RJ pointed out that it is better to keep the rpms down in the most efficient range to produce less heat.  I am not familiar with what difference there might be with a turbo, but going up the hill slower may also help.

I also added a mister system, which as some say is a band-aid, but it does help.  There are numerous variations on the systems people use.  Some just want to mist the air; other want to wet down the radiator.  Mine is of the wet-down variety.  I do thing it helps but is not something you see instantly on the gauge; it takes a little time to see the gauge respond.  Therefore, I use it before the heat climbs beyond what I like.  I'm sure that the warnings of mineral deposits on the radiator are valid, so cleaning the radiator will be another thing that will have to be added to your maintenance.

[RJ]

Bill -

Lots of good comments to help you with your heating challenge.

Some driving tips in this article, near the bottom, might help:

http://busnut.com/forum/index.php?action=articles;sa=view;article=41

IBME that 8V71s pull best with the least amount of overheating when running between 1700 - 1900 on a partial throttle.  If you can maintain your speed w/o black smoke out the exhaust on this partial throttle, you're good, usually.  If you can accelerate by going from partial to full throttle, you're good.  If you cannot maintain your speed w/o black smoke, it's time to downshift again.

Nobody's mentioned it but you: Western Colorado.  Sounds like you're in the Rockies, so you're what, somewhere over 4,000' elevation?  That alone is a contributor to your challenge - the thinner air "up there!"  So you have to adjust your driving habits accordingly.  What's a problem at home won't be in Kansas, for example.

Aesop's Fable - The Tortoise & The Hare perfectly describes this hobby/madness - we're the Tortoise!

FWIW & HTH. . .

[rdbishop]

bill,  disconnect your muffler and take it for a drive.  When I went to the turbo eng. I was told my old muffler would work just fine so it took me about three years to find out I needed a turbo muffler. No heating problems since!!!

Richard

[buswarrior]

And the other end too, where are you getting your intake air from?

Still thru that little hole ahead of the left side radiator?

Check Fred Hobe's page on cutting the side open to get more air into the stock air cleaner intake.
part way down this page:   http://users.cwnet.com/thall/fredhobe3.htm

And Fred's stuff on engine cooling is here:   http://users.cwnet.com/thall/fredhobe6.htm

happy coaching!
buswarrior

[Rick 74 MC-8]

The answer is yes. I have a switch that cuts power to the heat solenoid. (Defalt is open no power) I have on long hard pulls on hot days flipped that switch turned the heater blower on and watched the engine temp come down. Someday I would like to divert that hot air outside but as for your question YES it works. Ideal would be slow down



                                                                                                      Rick 74 MC-8