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Old 04-25-2022, 04:40 AM   #1
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Exclamation Help! Overheating?

I have a All American FE with a 5.9 Cummins, AT545 tranny, 103,000 miles. I bought it three weeks ago and drove it at 70-75 mph for 4 hours no over heating issues. Temperatures were cold but didn’t think much of it.
This week, three weeks later I took it on a trip, only difference being that I removed the under seat heaters and now it is overheating at 1800-1900 RPMS, 55 MPH and will exceed 220-230 F. in temperature. Since having the problem I have removed the thermostat to increase flow, changed the temperature sensor (located by the coolant inlet ie where the thermostat lived. Would love to know if there is another temp sensor elsewhere), emptied the entire cooling system, built up -20 psi to fill the coolant system to make sure there were no air pockets. I took a pressure washer to the radiator, took the inner cooler off to make sure there wasn’t dirt or bug build up between the two.
I can see that there is coolant circulation when I run it without a cap (replaced cap), also thought maybe the impellers on the water pump were shot but when I rev it to 1500 RPM with the cap off I have coolant shooting out like crazy, we have pressure.
Ladies and gents I am at a complete loss. I’ve also shot the inlet hose and other parts of the engine with a temp gun (which read lower by 10 ish degrees almost every time). The last thing I can think to do is have my radiator boiled out, possibly replace my temp gauge, or add electrical pusher fans to the front of the radiator, the factory one is mechanical.
Do I need to create some sort of additional trany cooler? Add a temp gauge to the transmission?
I don’t have the bus built out, it has maybe 1,500 lbs inside (seats etc have been stripped) and I’m towing a 90’s tacoma behind me 3,700 lbs, no trailer. The over heating problem persists with and without towing the tacoma, I’ve unhooked several times to test.

Oh, so it also sets off an alarm and the service engine soon light comes on when it reaches 225 F. Which I’m assuming is the engine temp safety feature.

I would love your suggestions etc.
Also I have no way of reading codes and I’m not familiar with the 9 pin system. Would an adapter from 9 pin to OBD2 work for a normal scan tool? I’m assuming it used the same CANBUS system hot, ground and then two sending wires. But I’m wondering if it configured differently?

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Old 04-25-2022, 07:08 AM   #2
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what about the fan? is the fan clutch engaging? at 220+ your fan should be on full speed with the high idle set at 1500 you should move tons of air.. if the fan isnt spinning like crazy what is the AIR TEMP coming out of the radiator? if the radiator is clogged internally you'll have high coolant temp and the air temp will be warm at best.


a bad fan clutch often results in the fan spinning at minimum speed and never speeding uo when it needs to.. this often manifests itself in warmer weather, as in cold weather it takes less air through the system to keep the engine cool.



I have replaced fan clutches on 2 of my 3 busses (and the 3rd doesnt have a clutch)..
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Old 04-25-2022, 07:37 AM   #3
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Reinstall the thermostat. Not only does it route coolant to the radiator once opened, it also plugs the bypass passage that's located beneath it. Removing it leaves the bypass wide open which circulates a bunch of hot coolant back to the water pump. Use the right thermostat too, most parts stores will sell you one that "works", but is actually too small and will cause overheating issues as well. Search on here as I mentioned this and gave pictures/part numbers before.

Did you remove all the heaters? or just the rear one? If you removed all, the lines get plugged, not looped, as that's another source of coolant bypass.

Finally, does this bus have shutters on it? are the functioning correctly and open?

As Christopher also mentioned, you're fan could be your issue as well, but I'd typically see that in the hottest days of summer, not now.
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Old 04-25-2022, 08:15 AM   #4
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What cadillackid said plus these.

I'm just going to address some of your statements.

Quote:
I removed the under seat heaters and now
The bus was designed so that it could be driven in the summer with the heaters turned off. Taking out the heaters will have no effect on a properly functioning cooling system. Does anyone think they designed a bus to only cool properly in the summer with the heaters turned on?

Quote:
removed the thermostat to increase flow
Did you test the thermostat, or put in a new one?
Many engines will overheat without a thermostat, the thermostat is a known restriction designed into the engine, without it water doesn't stay in radiator long enough.

Quote:
built up -20 psi to fill the coolant system to make sure there were no air pockets
Not sure what that means. Pressure, whether plus or minus, will not eliminate air pockets. Bleeding it will. Generally, after having a cooling system open, running an engine long enough for the thermostat to open and refilling is enough.

Quote:
water pump were shot but when I rev it to 1500 RPM with the cap off I have coolant shooting out like crazy, we have pressure
The water pump in a cooling system does not make pressure, it creates flow. The pressure comes from temperature rise. By "shooting out like crazy" does that mean it shoots up (not OK) or just gently rise and over flow (probably OK).

If it does indeed shoot up I would suspect combustion pressure getting into the cooling system. Are there bubbles in the water you can see in the radiator? Does the pressure rise very quickly, measured with a gauge, in the cooling system? Slow pressure rise, with rise in temperature is normal, fast rise is not. Does the antifreeze smell like exhaust? Does the exhaust have a bit of antifreeze smell?

Quote:
Do I need to create some sort of additional trany cooler? Add a temp gauge to the transmission?
Probably with a 545 but, if it overheats with out the towed on flat ground, it's not your problem.


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Old 04-25-2022, 08:58 AM   #5
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Quote:
Originally Posted by cadillackid View Post
what about the fan? is the fan clutch engaging? at 220+ your fan should be on full speed with the high idle set at 1500 you should move tons of air.. if the fan isnt spinning like crazy what is the AIR TEMP coming out of the radiator? if the radiator is clogged internally you'll have high coolant temp and the air temp will be warm at best.


a bad fan clutch often results in the fan spinning at minimum speed and never speeding uo when it needs to.. this often manifests itself in warmer weather, as in cold weather it takes less air through the system to keep the engine cool.



I have replaced fan clutches on 2 of my 3 busses (and the 3rd doesnt have a clutch)..


Iím not sure how to set the high idle as is doesnít seem to want to set anywhere above 1100RPM but then I do get the 1800 RPM the fan is very loud and pushing quite a lot of air. I donít have an air temp sensor, and how would I test the fan to make sure that it is not slipping?
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Old 04-25-2022, 09:09 AM   #6
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Originally Posted by somewhereinusa View Post
Did you test the thermostat, or put in a new one?
Many engines will overheat without a thermostat, the thermostat is a known restriction designed into the engine, without it water doesn't stay in radiator long enough. :
I will go get a new thermostat and put it in. That is a help thank you!!
Quote:
Originally Posted by somewhereinusa View Post
The water pump in a cooling system does not make pressure, it creates flow. The pressure comes from temperature rise. By "shooting out like crazy" does that mean it shoots up (not OK) or just gently rise and over flow (probably OK).

If it does indeed shoot up I would suspect combustion pressure getting into the cooling system. Are there bubbles in the water you can see in the radiator? Does the pressure rise very quickly, measured with a gauge, in the cooling system? Slow pressure rise, with rise in temperature is normal, fast rise is not. Does the antifreeze smell like exhaust? Does the exhaust have a bit of antifreeze smell?


Probably with a 545 but, if it overheats with out the towed on flat ground, it's not your problem.
:
My radiator cap is on the front of my bus facing sideways, so itís hard to see the normal flow you would if the cap is on the top of the radiator.
-20psi was in reference to a tool or process that people use to check for radiator leaks and fill a radiator without bubbles. There is a specific tool that I used to do that with it just creates a vacuum inside of the cooling system and then sucks coolant into that vacuum.
My coolant doesnít smell like exhaust , the oil doesnít look milky, and my exhaust doesnít smell sweet like coolant.
I will replace my thermostat first and then I will have the radiator boiled and rodded out.
I wonder at the clutch fan, does it need 1800 RPMS to operate at full speed?
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Old 04-25-2022, 09:49 AM   #7
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Make sure you open the faucet looking valve at the rear of the cylinder head after refilling the system. Air gets trapped there causing overheating. I had that exact problem and running it up to temperature with the heater valves open solved it. I believe you need to loop the coolant lines that went to the heater so you have flow.
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Old 04-25-2022, 10:45 AM   #8
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Quote:
Originally Posted by mhaisten View Post
Make sure you open the faucet looking valve at the rear of the cylinder head after refilling the system. Air gets trapped there causing overheating. I had that exact problem and running it up to temperature with the heater valves open solved it. I believe you need to loop the coolant lines that went to the heater so you have flow.
If you take all of the heaters out you do not need to loop anything. You can close the valves and remove the hoses. If you leave some of the heaters you need to have a complete loop with both valves open. There should be two, one near the water pump and one near the back of the engine.
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Old 04-25-2022, 10:51 AM   #9
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Not sure what that means. Pressure, whether plus or minus, will not eliminate air pockets. Bleeding it will. Generally, after having a cooling system open, running an engine long enough for the thermostat to open and refilling is enough.
When we change any cooling system component on a bus, it gets vacuum refilled, typically to 15 inhg, so I assume he meant he used a vac refiller to 20 inhg.

Doing so eliminates a large majority of the air pockets that can be located in a system. The ones remaining will be small and will typically purge themselves over time through normal operation.

It also can be a pain add coolant when the fill tube is sideways, like in a FE school bus. A vacuum refiller makes it a breeze.
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Old 04-25-2022, 11:22 AM   #10
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Quote:
When we change any cooling system component on a bus, it gets vacuum refilled, typically to 15 inhg, so I assume he meant he used a vac refiller to 20 inhg.
New stuff, I closed my shop 40 years ago.
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Old 04-25-2022, 01:06 PM   #11
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Quote:
Originally Posted by Booyah45828 View Post
When we change any cooling system component on a bus, it gets vacuum refilled, typically to 15 inhg, so I assume he meant he used a vac refiller to 20 inhg.

Doing so eliminates a large majority of the air pockets that can be located in a system. The ones remaining will be small and will typically purge themselves over time through normal operation.

It also can be a pain add coolant when the fill tube is sideways, like in a FE school bus. A vacuum refiller makes it a breeze.
Yes, I did use a vacuum refiller. I am currently at a radiator shop where they did a flow test. They said it was only flowing at 25% capacity so I may have just found my issue. Iíll keep you all up to date. Thank you again!
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Old 04-25-2022, 06:44 PM   #12
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Thank you all for the quick responses and help, I so appreciate it!!

Turns out that after a flow test at a radiator shop the flow was down by 75% so that right there was my problem. I installed a new radiator 4 hours ago and am back on the road! Thanks again yíall!!
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Old 04-25-2022, 08:34 PM   #13
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Quote:
Originally Posted by Mountainmanmitch View Post
Thank you all for the quick responses and help, I so appreciate it!!

Turns out that after a flow test at a radiator shop the flow was down by 75% so that right there was my problem. I installed a new radiator 4 hours ago and am back on the road! Thanks again yíall!!

Glad your back going! How much was a new radiator? Did they have a problem sourcing the right one?


I would still recommend a transmission temp gauge before summer gets here. Also, you have stated you do 2 things which cook the 545 as well as the motor. You go fast and you tow a fairly heavy toad. As summer gets here, you may find that your temps rise alot. Watch those hills and install an additional transmission cooler if temps rise much more than 200.
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Old 04-26-2022, 09:28 AM   #14
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IMO, a temp gauge is a must on a 545.
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Old 04-26-2022, 02:48 PM   #15
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Originally Posted by Booyah45828 View Post
IMO, a temp gauge is a must on a 545.
what guage do you recommend and how hard is it to install? also should I add a second cooler? I live in NC it gets pretty hot here and I hope to take it up to the mountains some.
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Old 04-26-2022, 04:37 PM   #16
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The one I have was a autometer unit that I bought with a pile of gauges, and it's threaded into a hydraulic fitting on the cooler outlet port of the trans. Read through my build thread and you can see it.

You can go mild to wild on it. Put the probe in the pan or cooler out. Factory put it in the pan IIRC. Try to stick with a good brand, the cheaper units tend to be unreliable. VDO seems to be a good cheap brand, but you'll have to buy the senders seperately.

As far as install is concerned, it's not too difficult. You'll have to drop the pan, drill a hole into it, install the threaded bung, install the senor, install the pan, fill with fluid, mount the gauge, and then run the wires. There are youtube videos on it for trucks that will show a similar process.
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Old 04-30-2022, 05:10 PM   #17
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Did you forget that you were running 70+ mph for 4 hours and didn’t have any problem? Then removed the under floor heater’s and instantly have overheating problems? Don’t run a Cummins without a thermostat. Take a look at Genos garage.com Cummins Registry if you need to know something about Cummins engines call them they have six extremely smart technicians from very different Background histories With Cummins and have top quality parts. I have been buying from them for years and they helped me with a no start problem that appeared out of nowhere.
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Old 04-30-2022, 05:19 PM   #18
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Or reinstall the floor heater’s and see if your problem goes away . You may have interrupted or bypassed the majority of coolant flow though the engine cooling system depending upon what you did with the coolant hoses you removed from the floor heater’s.
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Old 04-30-2022, 07:50 PM   #19
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Originally Posted by dozr62 View Post
Or reinstall the floor heaterís and see if your problem goes away . You may have interrupted or bypassed the majority of coolant flow though the engine cooling system depending upon what you did with the coolant hoses you removed from the floor heaterís.
what?
maybe he created an air pocket by delete but if he dont know how to del with a small air pocket then how would he ever deal with the air pocket after putting everything back together?
this aint a facebook group
we need the OP to respond to help him.
coolant systems are not wiring systems?
and neither should be cut until you know what your final plan is.
easier said than done on electrical but this thread is about coolant.
where is the OP.
where did you loop your lines?
1 pump or 2?
glycol system or water?
how many heat exchangers? heater boxes under the seats ?
none of that really matters if you got rid of them.
thats less that your motor cooling/heating has to do.
anything radiator relalated the air has to be burped out of the system
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Old 05-02-2022, 08:37 AM   #20
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Or use a vac refiller like the OP did, and most of your air pocket issues will be marginalized and work themselves out.

If you guys would re-read the posts in the thread, a radiator shop tested his old unit and found it to be 75% restricted. A new radiator put him back on the road.
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