Engine Cooling for MCI (7,8&9)

[JohnEd]

My Friends,

I have read numerious posts, over the years I have been an avid reader on this board, about over temp problems/concerns.  The last, and most bazarre, for me, was resolved by replacing the fuel pressure regulator.  Over-fueling sure makes sense when you read the answer, but till then???  Here is my question:  What are the steps to evaluate the cooling system and not guessing about snapped or slipping pump impellers and the such?  I read that the radiator should be able to drop the water temp at least 10 degrees.  My problem there is that suppose it isn't dropping that much...that might mean your air flow isn't sufficient.  First is, I guess, how much air flow do we need and how do we verify that that is not the problem?  Then, I guess, should we be satisfied with a 10 degree drop across the rad?  If we have the air flow and the rad is dropping, I guess it would be a matter of determining the water flow rate....again, how much and how?

If I verified that all those operating parameters was withing the normal range I could assume that the engine was creating to much heat for that system.  If it had worked before I can see where if I made that verification I would look for something like overfueling or an exhaust restriction.  What else might do it at that point?

Isn't this worth getting quantified and develpoing a bullet proof proceedure?

Thanks

John

[Slow Rider]

As a new busnut, I hope you get an answer to this, sounds interesting to me.

Frank

[JohnEd]

Frank,

Me too!  I am amazed that the "big guns" haven't jumped on this.  I'm sure they will, in time.

John

[belfert]

When Sean was having issues with his cooling I think he had a 10 degree drop across his radiator.  Those who replied seemed to indicate that his temp drop was not high enough.

Now, I do not know what it should be.  

[Chris 85 RTS]

I have been struggling with a cooling issue myself.  I have yet to find a diagnostic procedure that will without a doubt tell me what the problem is.  There are many possible causes, some of which are contradictory.  For example:

1)  Not enough air flow -- air not getting into radiator at speed, improper or damaged air dams, fan too small, fan over rev'ing, fan under rev'ing, slipping fan clutch or belt or hydralic drive, bad shrouding

2)  Plugged up radiator -- inside or outside

3)  Thermostats defective

4)  Water pump defective

5)  Engine RPM too fast -- coolant circulates too fast thus does not get cooled enough in radiator

6)  Improper coolant ratio -- 50-50 is recommended, yet straight water is said to remove more heat

7)  Collapsing coolant hose -- restricts flow

8 )  Cracked head

9)  Fuel return restriction -- improper spray and inadequate injector cooling

10)  Transmission heating coolant -- trans slipping causing excess heat

11)  Radiator too small for usage profile -- my bus is a transit and would run all day at 180 in city driving, but on highway overheats slowly

12)  Injector timing and cam profile -- EPA engines generator more heat

13)  Plugged exhaust system

I know there is more, just can't think of them right now.  So, you can overheat due to water moving too fast or too slow through the radiator, yet there is no way to check for this, or is there?  Just too many variables.

[Stan]

Like the bus itself, no two engines are the same, or the driver, or the conditions it is driven under. You can do like NASA and put sensors at every conceivable spot and record it all on a computer program. You will then have the "normal" conditions for your engine with you driving it. Deviations from normal may or may not be a problem and if you do any maintenance (change any filters, do a tune-up, change injectors) all your previous data is useless except y0u know that things have changed.

When you have a problem (sudden loss of power, over heating or smoke) there are a million threads on the BBS with suggestions on what to check. Nobody should have to come on a forum and ask the same question that has been asked so many times before. Come and tell us your problem, and all the things that you have already done, that were suggested in previous threads, and of course you have followed all the instructions in the bus and engine maintenance manual. At that point, there may be one or two experienced people who can pinpoint the problem.

[JohnEd]

Chris,

The heat generated by stop and go is greater than that generated by mantaining a steady cruise.  I think that proves that your rad is big enuff and you pump is ok.  An ex leak would be worse at stop and go cause the pressures are greater at acceleration.  Trans should heat less in a higher gear with the converter locked.

Maybe I am wrong but I think that the theory about having the coolant flow "too" fast is an old wives tale.  If you cause the pump to cavitate, that would be different.

You could see a colapsng hose by reving the motor while watching the hose with the engine at temp.

Without any other info I would think you have a problem associated with how the air flows around the coach at high speed.

John

[belfert]

I just emailed Detroit Diesel about the recommended coolant temp drops through the radiator and they said 10 to 15 degrees for a Series 60.  Did not ask about V92 series.

Their email is csc@detroitdiesel.com.  They may not have as ready an answer for the older engines

[JohnEd]

Belfert,

I am sure that a radiators performance is independant of the engine it is cooling.  I guess we have one piece of the question answered with your input.....15 degrees F, Min.  I noticed that odessy was getting a lot more drop and that should inspire us to take a reading of our systems when they are operating normally.

So if you pull over on a hill and your rad input from the block is 200F and the output from the rad is 185F we should not boil and clean that radiator to solve the problem?  Experts?

John

[belfert]

Belfert,

I am sure that a radiators performance is independant of the engine it is cooling.  I guess we have one piece of the question answered with your input.....15 degrees F, Min.  I noticed that odessy was getting a lot more drop and that should inspire us to take a reading of our systems when they are operating normally.

The engine manufacturer should know how much drop in coolant temperature they require from when the coolant leaves the engine to when it returns to the engine.

[mikelutestanski]

Hello:     I have a 72 7 and I do not have any great engineering answers but here are some things that can be checked and repaired..... first the air is pulled through the radiator and pulled through the fans and down to the engine compartment. So the fan belt is the easiest to check. Is it in good shape and tight when running (not floppy or cracked) is the pressure right on the cylinder  ?  Next consider that the air has to be pulled into the fans. where is the air coming from? Is it coming through the radiators or through the back door which has a broken or no seal ( rubber gasketing missing or bad) ?  THe whole compartment needs to be checked for holes or leaks the air should come through the radiators not around the radiator for example.    The fans have a shroud on each side with a rubber gasket like a large O fastened to the shroud directing the air into the center of the fans. Are the gaskets centered properly and are they in pieces or pieces missing? The gaskets get hard after time and need to be replaced. If the air is slipping around the fans then the fans are short cycling; the air is not going thru the radiator.....ARe the radiators clean. Have they been inspected lately to see what lies therein. Blowing air back the other way and observing the result is a start. A thorough washing will probably be the next step. THe radiator shutters and fan gates are other items to check if they are still there.  When the top compartment is shipshape then  check the bottom doors. THe air has to escape out of the engine compartment somehow. If in doubt mount an automobile fan on the door and blow the air out of the compartment to assist the fans above (ie to relieve any back pressure to the main fans).  SO if the above is not satisfactory in the case of the mci 7 you can change the fan scrolls and squirrel cages to mci 9 fans (they will fit but it requires cutting the bottom hole larger ) Some have changed the fan pulley to a smaller size to increase the rpms.   So these are a few items that can be checked and repaired before calling the engineers.  Diesel radiator will provide a 4 inch wide radiator that will fit into the compartment snugly which increases the capacity also.   ($850 or better each )    if you are diligent you can make it work   good luck and happy busing    MIKE from Dunnellon Fl

[Sammy]

Chris, does your RTS have a fan belt and the automatic belt tensioner??
Shut off the batterys, put rear run switch into the middle position, rear start switch into "off",and starter cut out switch (open the surge tank door,it's in there..) into the off position.
If it does, you should be able to manually turn the fan in one direction, and NOT turn it in the other.
The question about water pump flow: YES, you can fabricate something to watch the coolant flow of the water pump. I fabricated a testing device back in the late '80's to do this.Works great,real simple.
Defective fan belt tensioner is a common cooling system defect on the RTS.
Send me an e-mail for more details.
Hope this might help. 

[JohnEd]

Belfert,

I am a believer in DD and I take their word to the bank.  I "know" they were telling you what the MINIMUM temp drop should be.  If you upgrade you radiators to a larger unit you will get a greater drop. 

Anybody want to express an opinion here.  I'm open.

John

[buswarrior]

One more for the list of possible heat problems:

16) Restricted engine air intake (poor routing, plugged air filter, etc)

great list Chis 85 RTS!

happy coaching!
buswarrior