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Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Hi

We had a R model OSKHOSH that had the radiator re-cored due to crash damage and then the engine would

overheat. We rebuilt the engine and still it overheated.

Finally we checked the the temperature diff between top and bottom radiator tanks and found high diff temperature.

We found the re-tube core had reduced tube diameter and not as many tube, re-cored and all ok.

Good luck. 

Super Contributor

Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Fan clutch? Most rear engine buses have a hydraulic motor driving the fan. No clutch needed.
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Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Dave,

 

It is a rear engine bus, so the fan sucks air into the radiator.  Since the problem started, I replaced the fan clutch, and replaced the old stock metal fan with a high performance plastic one.  Neither improved the problem.

 

My mechanic flushed the motor.  And I have replaced the antifreeze several times.  Would this be enough to remove the stop leak?  I only had stop leak in my system for a few hundred miles of driving, and that was nearly 4 years ago.

 

Andy 

Super Contributor

Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Is this fan a blow or suction? Have you measured air flow across the radiator? Did you get all the stop-leak removed from the system? It's possible that some of the metal has been coated with stop-leak, which insulates and doesn't allow heat transfer.
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Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Hi Dave, thanks for responding.  I've been told by many people that you don't want to run a 3208 any hotter than 210 degrees for any length of time.  They are very good at blowing head gaskets - I know from experience.

 

When driving down the highway in summertime, I have to keep the bus under 55 MPH just to keep the temperature below 210 degrees.  If I ran at full speed (for this bus is 68 MPH), I have no idea how hot the engine would get.  Like I said in my message, this bus used to run less than 195 even in summer.  Something has changed.

 

Any thoughts?

 

Andy

Super Contributor

Re: At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

Just exactly what is the coolant temperature when you perceive it is "overheated"? Just because the coolant temperature is over 195 does not mean the engine is overheated.
Contributor

At Wits End - Can't Figure Out Why My 3208 Cat is Running Hot over 2200 RPM. Advice Needed!

I'm at wits end trying to diagnose an overheating problem with the 3208 engine in my 1990 Thomas converted school bus.  When the weather warms up, the engine runs hot at highway speeds over 2200 RPM (55 MPH). 

 

If anybody can offer me some advice here, it would be SUPER appreciated!  See below for a description:

 

 

History:

For the first 6 years I owned the bus, it never ran above 195 degrees, even in summer, unless it climbed a hill.  And then it would cool down quickly.

 

In January 2014, a truck jackknifed into the bus parked on the side of an icy road.  It was hit in the rear drivers corner.  The truck was moving about 5 MPH.  The damage was minor.  I drove the bus to North Carolina for repairs.  During the trip, the radiator sprung a minor leak from the damage, and I was forced to add “Barrs Leak” to make it the rest of the way.  In North Carolina, they flushed the coolant system, re-cored the radiator, fixed the body work, added an AC compressor to the engine and AC system to the bus.  When I drove the bus home in the fall of 2014, I was expecting it to run cooler with the new re-cored radiator.  It didn’t, and instead ran a little warmer.  When the weather started to warm up in the summer of 2015, I started to notice the bus running above 195.  The problem seems to be getting worse.

 

The bus runs OK in winter when the temperature is below 40 degrees.

 

Problem:

At highway speed in Spring through Fall over 2200 RPM, the bus engine warms over 195 degrees.  You must do at least 5 miles without slowing down before you’ll notice the problem.  Once the bus stops or slows below 2000 RPM, it cools quickly. 

 

Repairs:

  1. I pulled the radiator out of the bus 3 times and sent it to two reputable radiator shops.  Both shops told me the radiator was properly re-cored and working fine.
  2. Last summer I replaced the water pump. Nothing changed.
  3. Last summer I replaced the thermostats (2) with 185 degree ones from Cat. Before installing them, I tested them in a water bath to make sure they worked.  Nothing changed.
  4. Last fall, I replaced the fan clutch and added a new plastic fan that pushes 40% more air through the radiator. No change.
  5. Last fall I also added a second small 12V electric fan. No benefit.
  6. My mechanic flushed the engine last fall. No benefit.

 

Tested:

  1. Last fall I purchased a kit to test for exhaust gas in the radiator. Tested it several times and it showed negative.
  2. Bought a thermal infrared gun. Compared the gauge temperature with temperatures at the engine when hot.  The gauge appears to be fairly accurate.
  3. Just changed the engine oil and had it analyzed. The analysis showed nothing unusual.

 

Observations:

  1. The bus does not burn much engine oil. Usually a quart or two after a 300 mile trip.
  2. Small droplets of oil appear on the back engine door after a long trip. Has been happening for many years.  Have to wash the rear of the bus constantly.  It might be from oil drips under the motor.
  3. Never noticed any unusual smoke from the drivers seat.
  4. The engine runs smooth over 2200 RPM. Never noted any unusual vibration or noise.
  5. Have not noticed any loss of power over the years. It only has 225 HP, so it is an underpowered bus to begin with.
  6. Have always run the bus on the red truck antifreeze and distilled water. The bus has always had a coolant filter.  The old radiator was clean when they pulled it apart and re-cored it.  Whenever I have opened the engine, I have always seen the inside water passages as very clean.  There is no mineral or calcium buildup in the cooling system that I have ever seen.
  7. I have never had the valve lash adjusted on the engine. It is due – though I’m hesitating knowing I'll soon have to replace the engine.

 

Any ideas would be super appreciated!  I'm facing the reality that I might have to rebuild the motor, or purchase a new one.


Thanks again!!

 

Andy Coleman, Jackson, NJ