Help on heat

[danielmeguel/1974 MCI]

Hi folks, I need information on how to cool my bus. I have a 1974 MCI8, powered by a 8V71 with a blower and turbo, and a Allison auto trans. I have the original radiators but have 2 ea MCI7 radiators installed where the squirrel cage use to be. All radiators have electric fan with 19" blades. The 7 rad's are the primary rad's and 8's are the secondaries. All fans are on auto start set by thermastats with override switches on dashboard. I run around town and it seems to be okay but as soon as I hit a 4 to 6 deg hill temp rises to 220F. I have installed air scoops on the 8 rad's. Anybody had similar problems that they solved, I would appreciate some help. My bus is done and I'm ready to hit the road. Thank you in advance...........Daniel Tiburcio, Vallejo, CA

[bevans6]

This has been discussed several times, and the consensus opinion seem to be that electric fans can't move enough air to cool a two stroke.  The squirrel cage fans draw around 25 - 30 hp to move the air they do - that would take more electrical current than the 50DN alternator can put out.  But then someone comes along and does it successfully so we all have to take a second thought.

I have a concern about your MC7 rads located where the old fans were being the "primary" rads.  Where are they drawing their cool air intake from?  Where are you sending the hot air?  How do you have the fan's ducted?

Also I wonder if your primary/secondary rads are in series or in parallel to each other?  What makes one set "primary" and the other set "secondary"?  The original pair of radiators were in parallel.  Water flow through the radiators can be as important as air flow.  some feel that a greater difference between the water temp and the air temp yields better performance so running everything in parallel so each radiator gets the hot water from the engine directly, and all the outputs are pooled together into the water pump inlet.  Others feel that running two pairs of rad's in series works better.  One rad cools the water half way, the second rad cools it the rest of the way.  I personally favor running everything in parallel.

Others will have ideas, and welcome to the club!

Brian

[Len Silva]

Hopefully, you will get someone knowledgeable who can actually look at your setup and offer advice.  It's hard the troubleshoot from a distance with such a non standard system.

Trying to cool with electric fans, while not impossible, has rarely been successful on a bus.

I don't know a lot about MCI's except what I have read here over the past twelve years or so, but my gut feeling is that you are in for a lot of work, possibly restoring the original blower system, before you can be comfortable using your bus in a heat stress situation.

[Tim Strommen]

I did an electric fan in my bus once upon a time - didn't go so well...  I have even removed the eelctric fan from the pickup I drive.  In both cases, I noticed increased power availabiliy with the electric, but more often I saw the temp needle climb out of the thermostat controlled range (i.e. the thermostat was wide open and there just wasn't enough cooling happening while the water was in the radiator).

To take heat out of something you need to expose it to something cooler.  How much heat is lost from the high-temperature thing to the cooller thing is dependent on how efficient the heat transfer is, how much time the transfer is allowed to occur, and the total difference in temperature between the two.

Air-to-Air is less efficient in transferring heat than Liquid-to-Air, but Liquid-to-Air is still less efficient than Liquid-to-Liquid.  On a bus, the ammount of time can be altered by increasing the air flow through a radiator (bigger fan, or spinning it faster), or by decreasing the flow-rate of water through the radiator (which can be done by adding rows to the core thereby adding liquid volume to the radiator).  To increase the temperature difference, you can either overheat your engine (bad) or drive in cooler climates (not always possible).

Keep in mind that on an engine there are three ways that heat typically gets out of the engine:

• the water cooling system (about 45% of the heat)
• the exhaust system (about 30% of the heat)
• the engine block (about 25% of the heat)

A few things you can control:

Get the electric fans out of there.  Okay, you can leave them in if you are only using them as a back-up to a mechanically-driven fan or blower (hydraulic/belt/gear-driven).  Yes you will lose a bit of engine responsiveness and overall power, but that's because you aren't able to use power that should be going to cooling.  Seal the edges around your radiators so that air can only go through the radiator, not around it - a powerfull fan will cause a low pressure and the back side of the raditor, air has a nasty way of finding the path of least resistance... Make sure that you have the maximum water volume in your radiators possible - this may mean rodding your core or re-coring your radiator (if you have to do this, you might look into getting a few more rows added).  If there is scale/rust choking up your pipes, that blockage is both taking up space that water should be using thereby making the water go through the radiator faster (less time to transfer heat to the air) and it is also reducing the thermal transfer efficiency of the core (acting as somewhat of an insulator).  Insulate your exhaust manifold and pipes - you want to ensure that the heat the engine is exhausting is getting out of the tip of the exhaust pipe, not back int the engine compartment.  You can also ventilate the engine compartment, to blow more hot air away from the block - I have seen rear-engine busses going up long grades with the engine compartment door open.  Most cooling system designs take the hot air from the radiator and dump it straight into the engine compartment, not great, but most busses don't have a choice.  Add a rubber mud-flap the entire width of the bus (behind the rear axle, but ahead of the engine compartment) and around the sides of the engine compartment - as you move the bus through the air this will create a low pressure area in the engine compartment, pulling new air in and out under your bumper.  this also prevents hot air from coming out your radiator and going down to the ground and being sucked back in to the front of the radiator.  NEVER put a full width mudflap at the rear bumper!!!  This keeps hot air in the engine compartment!!!  As an absolute last resort there is always the mister option...  This way, you spray water onto the radiator core from the outside, and the evaporation of that water on the hot surface of the radiator reduces the external surface temperature of the core fins and pipes giving you that bigger temperature differential.

The mister thing is hotly debated on this forum.  Frequently.  It works, but the risk is that any dirt in the air being pulled through the radiator, or dirt alreadi on the radiator will turn into mud - and them solidify in place once the water evaporates.  This mud may block air from going through the radiator, and it may also contain chemicals that can eat your radiator core really quickly.

Lastly, why not slow down a bit?  What's the rush?  Take some back roads with a lower speed limit and a better view ;-).

-Tim

[wal1809]

I was told to get a new radiator.  I didn't want to afford one so I just drive 55 to 60 mph and watch the temp guage.  It has been fine even in 109 degrees.  If I go too fast though it will increase to 190.  i am going to limp it along that way until I have to fix it.

[TomC]

The hardest engine to cool is the 8V-92TA.  Quite simply-find the radiators from another MCI with a 8V-92TA in it, install where your radiators are, and reinstall the squirrel cage blower belt driven off your engine.  Those radiators will easily cool your 8V-71TA. 
Electric fans only work on stop and go-like transit buses since they have time to cool at every stop.  Electric fans were tried on big rig trucks-running 8-10 fans.  Didn't work.  Good Luck, TomC

[luvrbus]

Daniel, you are better off now just to pull your system and sell the parts and install a 1600 sq inch radiator with a 32 inch fan on the drivers side at the rear and use a Prevost 90* belt driven fan drive that will stop the heating issues you see it done on MCI's

It would cost a small fortune to restore your system back to the original setup,MCI charged me 1200 bucks just for a rebuilt gear box for the fans 

good luck

[robertglines1]

 To back up what Clifford just said I have had Mci with cooling prob.  Now have prevost with 8v92 and had problem keeping it warm enough to be efficient. That's at governed speeds year long; hills and all. put in higher thermostats to keep it there. So system is efficient.  Have often wondered why more didn't change over to this system. One rad to fool with and the gear box is much simpler.   Bob

[loosenut]

Have you checked the accuracy of your gauges?  You being on the coast it surprising that you're overheating.  I thought I was overheating going up hills in SD until I checked my gauges against an infrared thermometer. 

My gauges like yours would show normal temps on the flats but would zoom up to 210 on mile or two mile hills.  Once I started confirming dash temps by hustling back to the engine and taking thermometer readings off the freeze plugs, I found my temps were actually in the normal range 175-180.  I changed thermostats twice before the dash resembled the thermometer.

If you don't have one I recommend the thermometer.  It is one of my best purchases.

Mike