Need some input on a heating issue we're having with a Bell B40C (SN:BAT3958-98) that we just had the engine rebuilt in. The truck has started heating when pulling/returning from pulling a load but is otherwise fine. The problem goes something like this: - Check out the truck crank and warm up = no heating issues - Sitting in line to be loaded or running around on flat ground = no heating issues - Get loaded and head to the fill, generally down hill for about 800ft and dump = limited rise in temp which seems to be normal - Return to loading tool = Temp begins to rise to +/-90-95 Celsius - In line to be loaded again = Temp continues to rise and rises up to the hottest temp at or just over 100-105 Celsius but will begin to fall after about 90-120 seconds Below are the things that we have checked: - Water pumps was purchased new when the motor was rebuilt - Thermostats were replaced = no change in heating and you can see the gauge moving up and down to indicate they're opening and closing - Radiator pulled, rodded and dipped = no change in heating - Viscus fan clutch was pulled and wasn't free spinning or otherwise indicating that the oil was out of it etc. The engine is a Mercedes OM442LA. I called the shop that built the motor for us and what the tech there says is the temperatures I'm seeing don't sound to be all that hot and maybe this is a non-issue? I am not accustom to seeing these types of temps in the other haul units we have... Is this all in my mind?
Sounds to high. What is the temperature printed on the thermostat? According to the specification they are supposed to be 180*F (82*C). I am suspicious of the viscous fan.
I would question why the coolant temperature is rising at all when the truck is "hauling" loaded downhill - provided of course that your description of the loaded haul profile is 100% correct. With relatively high engine RPM and everything spinning at close to max speed but with little load on the drive train travelling downhill the coolant temp ought not to rise at all from whatever it was when he pulled out from under the loading tool. I'm not convinced regarding the engine shop tech's comment about the coolant temperatures being "normal". I wouldn't have thought the temperature of the system should rise much above 90 DegC at any time (unless there was a problem), much less to the 100-105 DegC range you describe, even temporarily.
I would also suspect the fan clutch. I have one time found where the serpentine belt was routed wrong and the fan was turning backwards
Below is the original thermostat that we pulled out. From what I can see its a 79 C thermostat?
Nige, Would a head gasket being installed incorrectly and plugging up a return port or something along these lines be a possible cause for heating? Would this be detectable with a laser thermometer shooting each head? Should we throw a new fan clutch at it or try and directly couple the fan to the motor? Grasping at straws here...
I'll ask you the same question I proposed to Nige, would it make since to direct couple the fan to the motor to eliminate the possibility of a under speed fan?
Have you tried using an infra-red thermometer to take the temps of the top & bottom hoses to/from the radiator for a kick-off.? Also have you ruled out Dave's thought of a serpentine belt wrongly installed and making the fan run backwards.??
Nige, I don't know that we have have hit them with the infrared thermometer yet. I will ask. I will have to look into the belt. I do not think that with the belt routing on this machine you can install it incorrectly. The belt us a v style not serpentine so I am pretty sure this would be ruled out.
What was the cause for rebuild? I would lock up the fan drive after you see what you have for a temp drop.
Nige, We checked the motor with a temp gun and we are seeing a 10-15 degree difference between the gage in the cab and the gun. I am ordering a new gage and sensor to see what they do for us. Might be a min before I get them unless there are some here state side. Most of these older units have to have their parts shipped in from South Africa....
We had a cam lobe worn slap off the cam shaft. Wasn't pretty.
That's one thing, but what temp difference are you seeing between the top and the bottom hoses in/out of the radiator.? See post #8 above.
We just got some parts in and are testing the machine now. Will let you know what we see and will confirm the temperature differential between the two hoses for you.
OK, so here is what we have. The new temperature gauge in the cab and new temp sending unit are confirmed to be working and check against the IR temp. gun. What we are seeing between hot side and cold side of the radiator are Hot:98C Cold:50C. I don't know how I feel about the cold side reading, seems way too dramatic, because there was a constant air flow across the face of the gun just about every where I could get to with the engine at idle to shoot it. I guess at this point I am questioning if the engine is actually running hot or not?.... After replacing the temp gauge and putting the truck on a hill and power braking it we aren't seeing the same temp rise as we were before so maybe we have gotten the issue resolved?.... Today the temp gauge only went to +/-105C when the engine was loaded. I've reached out to Bell but have not yet heard back on the acceptable temp range.
Acceptable temperature drop across the radiator from inlet to outlet should be no more than 10 DegC. More than that indicates lack of flow, the favourite culprits being an internally-blocked radiator or a water pump that is not circulating correctly. Air flow across the face of an infra-red temp gun will not affect the readings in the slightest. What will affect readings is how shiny (reflective) the surface is that you are pointing the gun at. Matt surfaces give more accurate readings than shiny ones.
I never knew that Nige of course I never work on anything shiny
I'll be honest I only found out by accident. Couldn't figure out why a heat gun was giving temp readings all over the place on a chromed exhaust pipe. For cooling systems I prefer to shoot the temp of the top & bottom hoses. Another thought I had. Seeing as the engine was replaced recently is there any chance that the cooling system has an airlock in it.? I have no idea what the layout is of the cooling system on this particular model.
I figured we were way out on temp drop. I am starting to think that there is an issue with the water pump as well. We pulled the radiator and had it rodded and vatted to have a clean fresh start and eliminate it as the culprit. We did pull the new water pump off and inspected it. We did not see anything out of the norm. The impeller looked good and there were no other obvious signs of wear or leakage. Maybe it needs to be replaced again for good measure? I have found a place in Texas that supplies parts for these MB motors here state side with good selection and pricing. Good to know about the temp gun. I was shooting the hoses and the radiator housing itself to get the readings. So the readings should be good to go. this at least confirms our temp sending unit and gauge are working properly.
No sure about the air lock. How would I go about looking into that? Attached is a layout of the cooling system the hot side is the hose entering on the left side of the radiator. I will see about getting a picture of the engine compartment.
An off-the-wall thought but I’ll throw it out there anyway. If that Merc engine is used in all sorts of applications is there more than one type of water pump (LH or RH rotation) available for it and you’ve got the wrong one.? I guess your engine rebuilder would be able to answer that.
Nige, That's an excellent point. I would even bet that there could be different flow rates for the engine. Crane vs haul truck would have much different needs for cooling I'd imagine. I am going to look into this some more. Thank you for the idea to chase down.
Following up on this on going issue. We have gotten the engine rebuilder involved on this engine now because we have replaced the temp sensor and gauge, fan clutch, thermostats, water pump and sent the rad out to be rodded and vatted and we're still over heating when the engine is loaded. They're asking around their staff to see what they think it could be, but they have thrown out two items that I'd be curious to get your thoughts on. They said that the impeller on the water pump could be slipping on the shaft as engine speed increases or there could be an air pocket in the block. I could see the impeller slipping being a possibility because the truck wont run hot until its put under a load and the RPM's are run up. The shop manager said it was a common issue with some of the Cummins engines used in on highway applications so maybe that happening here? To check this I guess we would need to pull the pump off and check that the set screw (if it has one) is tightened up? If we were to check for an air pocket in the motor how would we go about getting at that? Would the air not be absorbed into the coolant over time? This has gone beyond frustrating at this point.....
Normally if you can bleed the air from the highest point it will get the air out if it has a after cooler you need to loosen the water line untill water flows out Cummins has a petcock to do this. I would think if it was a air bubble it would heat no matter what
Update on the engine saga. The company that did the rebuild has asked us to pull the exhaust pipes off the manifold and run the truck this way and see if there is restriction causing over heating. We plan to try this later this week after we get the water pump back on after having checked it again and confirming its not slipping. I also had another idea thrown at me which is the fuel system could be running too lean and thus causing an over heat? Does this sound right? I am not even sure where to start on how to check the fuel to air ratio?...
Answer these for me since I just found this thread 1. How does the engine run? Is it smoothe through the rpm range, unloaded and loaded? 2. Is there excessive black smoke out the exhaust when under a heavy load? 3. What is the hottest temp you have seen with the ir gun at the thermostat housing versus what the gauge is showing at the same time? 4. Is the temp sender near the exhaust and is the exhaust leak free? The thermostat is a water flow and temp regulator. Its job is to keep the engine at a specific temp range and adjusts the water flow accordingly. The coolant in your system absorbs heat......the airflow through your radiator cools the coolant. Being that from what I have read so far.....it sounds like the timing may be a bit off under the engine load and creating excessive heat. JMHO of course
On diesels if you were running lite on fuel it would kill the power and the turbo boost. Does it have low power you could check the boost pressure and see if it is low or not
Power has seemed to be fine. When I ran the truck in the spring it pulled fine to and from the fill. I have not checked out the turbo pressure. Will have to look into this one more to come up with a way to test it.
We disconnected the exhaust today and ran it around some then power braked the unit on a hill and we did not run hot. The highest temperature we got up to was about 95C. So far as we can tell we might be able to live with a temp. of that range while hot. We plan to go ahead and straight pipe the truck and put it back into the field. Maybe we have finally solved this on going issue... time will tell.