SECTION 05
CHANGING ENGINE COOLANT
20.1 Introduction
One of the most often overlooked maintenance requirements is changing and maintaining the chemistry of the fluids in the engine cooling system. It is understandable in the context that it is not any easy task, a large amount of waste coolant is generated, and a lot of containers for the spent engine coolant are required along with a suitable waste site.
The system on our buses holds around 22 gallons. It is difficult or impossible to list a quantity that holds true for all coaches because there are so many variables that will affect the total capacity, such as converter installed systems.
Failure to change the coolant on the specified schedule which is 200,000 miles or two years (whichever comes first) can adversely affect everything from the radiator to the life of the engine.
Since coolant changes for our coaches will take place every two years, that should also be established as the schedule for inspecting and replacing hoses as necessary. Since draining the coolant is such a time consuming project, it is best to avoid doing it for repairs between coolant changes so I suggest while draining the system you take the opportunity to examine every part of the cooling system, with special attention given to the hoses and clamps added by the converter.
20.1 Tools and supplies required.
The most critical requirement is to have a drain pan or containers of sufficient size to hold the removed coolant. You will also need a filter wrench of a size suitable for the removal of the Detroit Diesel coolant filter. Additionally if any hoses will need replacement a screw driver or socket wrench of the correct size will be required to loosen and tighten hose clamps.
About 22 gallons of premixed or 11 gallons of concentrated anti freeze the meets the Detroit Diesel specification for the engine is required along with a new coolant filter.
20.2 Draining the system.
Prevost recommends shutting the valves to the heater lines. On an older 8V92 coach this might be the gate valve behind a flap forward of the radiator accessible through the radiator door on the driver’s side of the coach. On later model coaches this might be valves located in the compartment housing the Webasto. Not all coaches will have the heater line shut off valves located as described above.
Prevost lists four valves to be opened for draining the system. They are the engine drain cock (near the bottom of the engine on the same side and below and forward of the thermostat housing), the thermostat housing drain cock, the water pump drain cock, and the radiator drain cock. I have used the lower tubing drain cock located near the coolant filter in lieu of the radiator drain cock.
Coolant is poisonous, so I use extreme care to capture all the drained coolant. It is almost necessary to wire or tie funnels beneath the drain cocks and direct the flow into the drain pan or containers.
20.3 System inspection
While the coolant is draining, this is the perfect opportunity to inspect all hoses and clamps. Depending on engine type, converter, location of various heater, and other factors the number and locations could vary. Pictured below are several areas to look and types of hose and clamp to inspect.
This is an engine hose on an 8V92. It is typical of all engine hoses which use a high quality material and have generally good life.
This is another example of an engine hose. These types of hoses are generally installed by either Detroit Diesel or Prevost. Look for bulging, any evidence of cracking or aging, and a good rule to follow is if in doubt, change it. Note the clamp type is not the typical worm gear clamp. When replacing any hose replace the clamps as well with the same size and type.
This is likely a hose section installed by the converter. The life of this type of hose is considerably less than the life span of the hoses installed by Detroit Diesel or Prevost. While the hoses may have a good appearance, examine the hoses carefully, squeeze the hose, check the clamps, and make sure the clamps are not corroded or broken and the hose section is not spongy, cracked or exhibiting any signs of decay.
These hoses are associated with the Webasto on this coach. Examine the hoses inside the coach at the heat exchangers also. They are the same age as the hoses on the exterior and are as prone to aging failures. I want to draw your attention to the short section of vertical hose in the center of the photo. When this photo was taken I failed to notice the evidence that the top clamp was partially broken. The sign of this is the end is tipped upward and it is not aligned with the portion around the hose. Also, notice the slight discoloration on the floor beneath the hose. That was a sign of slight leakage that also should have been noticed. After the next trip the top of the hose connection had started dripping. The message here is clear. Look for any defect, regardless of how minor, and keep the bus as clean as possible so any leakage is easy to notice.
On my 8V92 I had some sections of hose located out of sight on the top of the engine. They were only visible and accessible from the panel beneath the bed.
These sections of hose, shown above, are located at the top front of the drive axle area, above the structural steel box section. Imagine how difficult it would be to replace these if they failed while you were on the road. I added the extra hose clamps to stop a pesky drip, and also because if a substantial leak did develop, these are out of sight and difficult to access.
I failed to notice the deterioration of various hoses that were out of sight on my first coach and only because an easily accessible hose failed did I become aware of the condition of hoses throughout the coach. As a result I would strongly urge that you carefully inspect the entire cooling / heating system in your coach with every coolant change, and as a recommendation do not let your hoses get older than ten years at the most.
20.4 Coolant filter replacement
Prior to refilling the system, remove and replace the Detroit Diesel coolant system filter(s). Be sure to lubricate the gasket and gasket surface with a light coating of white grease.
20.5 System filling
Close all drain cocks, verify all hoses that were replaced are properly clamped and the system is ready to be refilled. If the coolant is pre-mixed add it directly from the container to the radiator header tank (surge tank). If you are using the concentrate that must be mixed 50/50 alternately adding a container of coolant and a container of water that meets the Detroit Diesel requirements.
Fill to within 2” of the bottom of the filler neck. Open the heating system valves and start the coach, allowing it to come up to operating temperature. Periodically monitor the level in the tank to insure it still has coolant. Add as necessary.
To insure the entire system has had any entrapped air to be purged, operate the Webasto or other type heating system and the bus heating system. After running all systems shut the bus down, allow it to cool and recheck and refill the coolant system if necessary.
20.6 System inspection
Before taking the coach on the road, re-inspect all hoses, especially those that were replaced. Insure there is no leakage. Check for leakage around the gasket of the coolant filter.
20.7 System chemistry
It is critical that the chemistry of the cooling system is properly maintained. How you choose to do this, either through additives or the use of coolant with the inhibitors it is important that you monitor the system chemistry. I have been successful in maintaining the proper chemistry with the use of Detroit Diesel engine coolant and replacement of the coolant filter (which maintains the chemistry through inhibitors which are introduced by the filter). You can buy coolant test strips from Detroit Diesel or from other sources, such as Nal-cool.
20.8 Road test.
Sometimes despite your best efforts it will not be possible to eliminate entrapped air from the system. I allow time for a test drive, which will bring the coach up to its maximum operating temperature. I will stop and check the fluid level after the coach has reached its maximum operating temperature. If I feel it necessary to remove the cap from the tank, I use a large cloth to shield me from hot coolant and I turn the cap until the internal pressure is released. I refer to the sight glass, but the cynic in me uses a wooden rod to determine the true depth of the coolant in the radiator header tank.
Jon Wehrenberg 12/15/2005