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Discussion Starter #1
long story, but I'm overheating now while driving at highway speeds. Got it up to 230 or so before stopping to cool it off. Driving downhill doesn't seem to cool it back down to the 180-200 range where it used to hang out, but it drops a bit. I checked the thermostat, and it opens like it should in boiling water (opening just before the water starts boiling). I'm seeing some bubbles in the rad filler at idle, but the engine won't heat up much beyond 160 degrees at idle (even after 45 minutes)--also there's a lot of splashing from vibrations, so it's tough to tell if there are actually air bubbles, or just splash bubbles. The water pump pulley spins as it should by hand if I remove the belt, and spins fine with the belt. The stock (large) radiator was recently pressure tested. Boost and egts are normal.

How I got here:
mt 35 delivery van converted into a heavy RV. Engine runs great, and generally has been cool-blooded. At the beginning of July, my fan clutch failed, and sent the fan into the rad, which gashed it. The Engine got HOT (like 240) for around 10 minutes of re-filling, and cooling off before I could stop. Found a repair guy to soldier the rad, he pressure tested and flushed it. I haven't noticed it leaking. I drove all the way from Canada to WV (15 hours) with no radiator fan and the engine barely ran any hotter than normal. Over the last month I sourced a new fan clutch and fan. The vehicle has sat for the past month, and now has the new fan. It hasn't been losing coolant that I've noticed. This whole story may be unrelated.

BUT as I tried to leave today, after 10 or 15 minutes of highway driving in the mountains of WV, the temperature started to climb steadily (even just driving 55-60). Uphill it seemed as though it would max out the gauge at 240 if I kept at it. Downhill it'll slowly drop to around 200-210.

Sorry for the long post, but would there be another test to rule-out head gasket? I'd assume that I'd be losing coolant through the engine (haven't noticed unusual smoke or coolant-smelling on start-ups)? What to try now?
Thanks!!!
 

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Long shot. Any chance that the new fan is opposite rotation (i.e. blowing air forward instead of pulling air in thru the radiator)?
 

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Russ I was thinking the same thing but did he say it worked for a while? I’ve been having over heating issues myself (nothing serious) and it’s weird the way these engines can act. Mine runs hotter at the front than at the rear. I’m hooking up a switch to turn my fan on manually as the sending unit for the fan is at the back of the engine where it’s supposed to be. I’ve had an air pocket issue also.No smoke or oil in radiator so I wouldn’t think he’s got a problem from it getting hot.
 

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Try a new T-stat, OEM preferably. Then dig deeper. There is a kit to test for exhaust in your radiator but I'm not sure if it works on diesels. Next would be to check for good flow on the radiator. Sometimes hoses will collapse on the "suck" side of the water pump too...that's hard to catch..
 

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Discussion Starter #5
thanks for the feedback everyone. I tried the new fan oriented both ways and didn't really make much of a difference. I'll try a new thermostat first, as it's cheap. My lower rad hoses are short sections of hose that run through a solid tube, so it's unlikely that they're collapsing, but I'll go ahead and replace them too. Anyone have any luck with Thermostats that can be gotten at Autozone or O'reillys? I'd love to avoid having to order an OEM one, but I will if it's clearly better.
Stephen
 

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An air bubble in the system would be one possible. A blown head gasket could be another. You've checked the thermostat which appears to be functioning correctly. You mention a new thermostat being cheap. Be careful there. Genuine Cummins thermostats tend to be kind of expensive. There is also more than one style used on these engines. Could the water pump possibly be bad? Just because it turns easily doesn't necessarily mean it's working correctly. The do fail sometimes. The style with the enclosed impeller like in the photo below is the preferred type.
 

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Discussion Starter #7
Thanks, Char. How would I find and/or eliminate an air bubble? I have a new Thermostat ordered from Fleet Pride--they claim that it's high quality (though not OEM--maybe Gates?). I'll go ahead and replace the lower radiator hoses too. I'll pull the water pump today. As I look at it, should it be fairly obvious if it's not working? I'd assume that if the impeller is turning properly with the pulley that it's working, no? THANKS!
Stephen
 

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Goat, the issue might be which thermostat. There is more than one design. You'd want the one spec'd for the specific engine. BoyJeenyus, check the water pump impeller to be sure it's still tight on the shaft. As for checking for an air bubble, might remove either the temp sensor or heater port pipe at the top front of the head while you fill it with coolant. Engines that had the water aftercooler have a petcock valve you open to let the air out when filling.
 

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I always start over-heat diagnosis with an IR thermometer.

First, to confirm that the temp gauge in the truck is accurate. Then, to look for "cool areas" in the radiator core.

If you already have the thermometer, or can borrow one, this is even cheaper than changing out a thermostat.

Roy
 

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Discussion Starter #13
Great idea! Unfortunately, my air cooler is in front of most of my radiator, so it'd be hard to check most of it :(. Thanks for all the suggestions everyone!
Stephen

I always start over-heat diagnosis with an IR thermometer.

First, to confirm that the temp gauge in the truck is accurate. Then, to look for "cool areas" in the radiator core.

If you already have the thermometer, or can borrow one, this is even cheaper than changing out a thermostat.

Roy
 

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Discussion Starter #14
UPDATE AND NEW QUESTION: OK, I'm pretty sure that I figured it all out. This fan and clutch are made for counter-clockwise rotation, and mine spins clockwise (looking at it from the front). I foolishly assumed that by reversing the fan on the clutch that it would actually pull air in the other direction, but watching it spin, this is not the case.

Based on some earlier threads on this site, I was able to get the autozone duralast fan clutch #922784, and after spinning down the nub at a machine shop, it fits fine. My main question is can I use this fan clutch to spin clockwise, AND does anyone have a part number for a fan 18-19.5 diameter that'll fit this fan clutch AND work spinning clockwise--I'm happy to alter my fan shroud based on size. If this fan clutch just won't work rotating the opposite direction, does anyone have a part number for one that WILL work with clockwise rotation? THANKS!
Stephen

PS this has been a learning experience for me. Thankfully I only replaced the thermostat and water pump so far, which hasn't been too expensive--and I consider this to be routine maintenance parts for an engine at over 200,000 miles anyway :)
 

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I see that it's listed counterclockwise. My question is whether anyone has a part number for a clockwise rotating one, OR if this one that's listed counterclockwise could actually work spinning either way? What is it in a fan clutch that would cause it to only work in one direction?
Thanks!
S
 

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I see that it's listed counterclockwise. My question is whether anyone has a part number for a clockwise rotating one, OR if this one that's listed counterclockwise could actually work spinning either way? What is it in a fan clutch that would cause it to only work in one direction?
Thanks!
S
Some one else willing to attempt an explanation why a one-way device will NOT work in the opposite direction????
 

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UPDATE AND NEW QUESTION: OK, I'm pretty sure that I figured it all out. This fan and clutch are made for counter-clockwise rotation, and mine spins clockwise (looking at it from the front). I foolishly assumed that by reversing the fan on the clutch that it would actually pull air in the other direction, but watching it spin, this is not the case.

Based on some earlier threads on this site, I was able to get the autozone duralast fan clutch #922784, and after spinning down the nub at a machine shop, it fits fine. My main question is can I use this fan clutch to spin clockwise, AND does anyone have a part number for a fan 18-19.5 diameter that'll fit this fan clutch AND work spinning clockwise--I'm happy to alter my fan shroud based on size. If this fan clutch just won't work rotating the opposite direction, does anyone have a part number for one that WILL work with clockwise rotation? THANKS!
Stephen

PS this has been a learning experience for me. Thankfully I only replaced the thermostat and water pump so far, which hasn't been too expensive--and I consider this to be routine maintenance parts for an engine at over 200,000 miles anyway
According to AutoZone specs on that number it is for counterclock rotstion
 

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Discussion Starter #19
Yeah, I got that. Anyone know what fan clutch will fit this engine and is made for clockwise rotation?
Thanks!
Stephen


According to AutoZone specs on that number it is for counterclock rotstion
 

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This is a bit puzzling. You cannot use a different rotation fan clutch unless you change the hub pulley assembly. The clutch inside the unit is designed for one direction only. That fan hub you have was not designed for a B series Cummins. Did you turn down the pilot on the hub or increase the pilot in the clutch flange? Cummins hubs and fan clutches should have a 1" pilot. Base 4bt hubs used 4 8mm bolts in a 50mm circle. Industrial hubs used 4 10mm bolts in a 60mm circle. You might check fan hub 922707 which is clockwise but it's not HD. Don't know what the pilot hole size is either. I found a listing for a 4bt hub and fan but don't know if it's the industrial bolt pattern or the standard. Whichever, you would need some smelling salts if you bought one of those as it's over $500 for the clutch assembly and fan blade. Ouch. I checked Uptime Truck Parts and they show an 18 fan blade, but no clutch assembly. Cost wise, you could probably change the hub assembly and pulley to one from a Dodge and use a Dodge fan clutch assembly if the fan isn't too big.
 
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