Last month I talked about the problem with my Cat 3208 shutting down. I do now believe the engine was overheating - not a faulty indicator. What causes a diesel engine to overheat? Coolant? Oil? Air filter? How can this be prevented - what preventive maintance needs to be done?

Thom
1990 Regency Widebody 38'
Cat engine Gillig chassis

Lots of things will cause you to overheat - Diesels, like gas need proper attention in the cooling system. I'll offer up some advice and observations on the diesel trucks we chase. This happens with gas or diesel so listen up. Some are strange but all happen at least once a year.

Flush out you radiator. Years of deposits, goo form in the radiator and it may need attention.

Air flow over the fins. The fins could have leaves or dirt inside between the fins. Use water from a garden hose to clean between the fins. Do not use a steam jenny or power washer!

Fins on the radiator could be bent. Use a fin straightening tool to allow airflow thru the radiator.

The motor is being lugged down. Try down shifting to the next lower gear. If all you have is an automatic then this happens a lot more.

On rear mounted engines in buses. They have a driveshaft, hydraulic motor or belts turning there off set cooling fan. Something in there fails.

The thermostat is sticking or not opening all of the way.

The impellers on the water pump are slipping on the shaft.

The belts are missing or are loose.

Low coolant level.

Blown headgasket, cracked head, pitting in the lining. Anything that causes compression to get into the cooling system.

Your fan shroud is missing.

Your fan blades are broken, pieces are missing.

Your transmission is overheating.

Your lower radiator hose is sucking shut from a missing spring inside of the hose.

Check your fan clutch. A fan clutch kicks on when the engine coolant reaches a set point. Kicks out after it cools down. I would check this out. High on the list!

***In a diesel most of the times it's an air operated sending unit inside of a water jacket that opens up (or closes off) and forces air into the fan clutch and locks it up. (Sometimes it's a lack of air that locks it into place.)
***In a gas motor a spring coil located in front of the fan expands and moves a hydraulic plunger causing the fan to lock in and run direct instead of slipping.

------------In both instances (air/fluid) this is done for noise reduction and an increase in mileage. Listen for the fan clutch to kick on - If your starting to overheat and it doesn't ROAR to life have that checked out.

The odd file...

Your fan blades were reinstalled wrong (backwards) after a repair.

You still have that piece of cardboard between the radiator and a/c that you put there in January.

Some motors have 2 directional (right hand/ left hand rotation) water pumps and you got the wrong one.

The picture of Jesus, Richard Petty, Elvis, etc... is zip tied in front of your radiator.

Your motor is too small for the application or our overloaded beyond belief.

!!!Major engine damage will follow if you keep running hot!!! Some motors are more prone to failure if overheated.

Bill N.Y.

According to a friend who restores antique vehicles and is considered to be a "master mechanic", another little known problem that can cause a diesel engine to lose power and stall when under load such as on a hill is from the valves being adjusted too tightly. this traps heat that would be expelled in the exhaust, causing internal temperature to rise high enough that the engine will no longer run, WITHOUT the temperature guage showing the engine is overheated. (He explained that the valves close too quickly, not allowing enough heat to be expelled with the exhaust gases. this raises internal temperatures to excessive levels when the engine is operated under load.) Once the engine cools off, it operates fine.

Had this problem on an old Isuzu P'up; discovered what was up as it was being sold-a few weeks after the valves were adjusted by a disreputable mechanic who was too proud to say he didn't have a clue how to work on the engine in that truck. (Austin Mobile Mechanics in Austin, Texas)
The new owner rebuilt the engine himself while renovating the truck and discovered EVERY valve was set differently; all set too tight. When he finished he said the valve adjustment was the only real problem he'd found that interfered with the engine's performance. (other than minor oil leaks and somewhat worn rings... it only had 124,000 miles on it.)

hope this is helpful, and good luck!
geoffrey

Some of the Cats (I know it is/was on the 3116 and 3126) had an oil leak that caused oil to be blown into the radiator an really cut down cooling capacity. I don't know if the 3208 had the same issue, and I don't remember the source of the leak.

Thanks to all. Certainly has given me a list to check next month when we return.

Thom