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Old 01-07-2019, 12:49 AM   #1
Mini-Skoolie
 
Join Date: May 2018
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Year: 2001
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Chassis: Freightliner
Engine: Cummings 6 cylinder diesel
Cummins 6 cylinder possibly overheating need help or advice.

So I'm driving from Florida to Philadelphia in my bluebird Cummins 6 cylinder with a hundred twenty five thousand miles on it. I'm driving about 55 and 65 miles an hour. Never going higher than that and my water temperature seems to be staying at 220. Since this is the second long distance trip I've taken with this bus I was wondering if anyone could tell me if this temperature is safe. When I get off the highway and put the bus into Idol it immediately drops down to about 180 200 degrees. Is it normal for a Cummins diesel School Bus? I was also thinking Petsense it immediately cools down when I get off the highway instead of slowly cooling down like an overheating engine I should be safe. But then again I've no diesel mechanic
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Old 01-07-2019, 07:05 AM   #2
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is this an FE bus? a conventional? im assuming cummins 5.9? whats the outside temperatures and terrain? are you climbing hills? if its warm outside and you asre getting hot on the freeway ,id begin to suspect the fan clutch is not engaging as it should.. this esp true if when its colder outside the bus seems to run cooler.. .. and since it cools right down when idling or driving in town..



if the heat condition occurs when its cold outside even then i'd begin to suspect a partially stuck thermostat, clogged radiator, or somewhat low coolant..



in a rear engine bus the fan clutch is even more importanbt as you cant rely on natural air-flow across the radiator..



-Christopher
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Old 07-01-2020, 07:18 AM   #3
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Hey Anthrobus, ever get to the bottom of your temperature issue?

We recently bought a BB TC1000 with the 24V 5.9 and experienced the exact symptoms you described on the drive home from picking up the bus. 500 miles from Alabama to Ohio - rolling hills the whole way with outside temperatures 70-80-ish degrees. Would cool right down to 180-200 almost immediately after pulling off highway, but would stay pretty steadily at about 220 on the highway.

You could definitely hear the fan kicking on, which is supposed to happen at 205. It was pretty loud with that fan running almost the whole drive.

Haven't torn into the system yet, but I plan on replacing whatever thermostat is currently installed with an OEM thermostat. I'll probably also do a radiator flush and coolant drain and replace.
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Old 07-01-2020, 07:56 AM   #4
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My guess is that you have a 545. That makes extra heat at highway speeds.
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Old 07-01-2020, 08:01 AM   #5
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We have the Allison 2000 series in ours. I have the maintenance records and it looks like the school replaced the thermostat with a cheapo part a few years ago.

I'm going to order an OEM thermostat and see what happens.
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Old 07-01-2020, 10:00 AM   #6
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Originally Posted by Ourversionoflife3 View Post
You could definitely hear the fan kicking on, which is supposed to happen at 205. It was pretty loud with that fan running almost the whole drive.

Haven't torn into the system yet, but I plan on replacing whatever thermostat is currently installed with an OEM thermostat. I'll probably also do a radiator flush and coolant drain and replace.
Good call, There is a difference between oem and parts store thermostats.

The oem one for 98.5-02 should be a high flow job and should look like this.


The parts stores will often supercede that one with the 03-07 thermostat which isn't a high flow version. That thermostat looks like this

The newer thermostat will work in the older engine, but in my experience it causes it to run hotter then the correct thermostat.
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Old 07-01-2020, 10:36 AM   #7
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Where would you look for a high flow version like the one in the first picture?

I tried to get one directly from Cummins from the online parts catalog, but it was unclear what exactly they had. There is extremely little descriptive information on the parts catalog system. The online system is also very clunky to use.

I just ordered a Stant thermostat off of Amazon that is supposedly what was installed at the factory. However, it looks like the one in the second picture.
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Old 07-01-2020, 10:39 AM   #8
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Quote:
Originally Posted by Ourversionoflife3 View Post
Hey Anthrobus, ever get to the bottom of your temperature issue?

We recently bought a BB TC1000 with the 24V 5.9 and experienced the exact symptoms you described on the drive home from picking up the bus. 500 miles from Alabama to Ohio - rolling hills the whole way with outside temperatures 70-80-ish degrees. Would cool right down to 180-200 almost immediately after pulling off highway, but would stay pretty steadily at about 220 on the highway.

You could definitely hear the fan kicking on, which is supposed to happen at 205. It was pretty loud with that fan running almost the whole drive.

Haven't torn into the system yet, but I plan on replacing whatever thermostat is currently installed with an OEM thermostat. I'll probably also do a radiator flush and coolant drain and replace.
Is this the bus that had the check engine and check transmission lights on?
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Old 07-01-2020, 10:53 AM   #9
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No, we passed on that one. No lights on at all on this one. Running good, just warm.
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Old 07-01-2020, 01:55 PM   #10
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Originally Posted by Booyah45828 View Post
Good call, There is a difference between oem and parts store thermostats.

The oem one for 98.5-02 should be a high flow job and should look like this.


The parts stores will often supercede that one with the 03-07 thermostat which isn't a high flow version. That thermostat looks like this

The newer thermostat will work in the older engine, but in my experience it causes it to run hotter then the correct thermostat.
I've dealt with that many times as well. Parts store thermostats are almost universally crappy vs the oem. I tried to be cheap and convenient and run a parts store thermostat in my miata. The oem one runs cooler and fits better.
Do the Cummins only have one thermostat? I thought most medium duty diesels had two.
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Old 07-01-2020, 02:17 PM   #11
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I should have one on the shelf, I'll get up to look for it here in a bit to get you the part number.
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Old 07-01-2020, 02:20 PM   #12
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Originally Posted by EastCoastCB View Post
Do the Cummins only have one thermostat? I thought most medium duty diesels had two.
ISB only has one. Certain engines have 2, just depends on the manufacturer.
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Old 07-01-2020, 02:42 PM   #13
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pn 3946849 for 98.5-02
pn 5292712 for the newer engines.

If you're not near a cummins dealer, look for a chrysler dealer and those parts should be on the shelf.

Both thermostats are 190, I've seen it stated otherwise elsewhere. The difference is in the design and how it plugs the warm up passage.
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Old 07-01-2020, 03:13 PM   #14
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Quote:
Originally Posted by Ourversionoflife3 View Post
Where would you look for a high flow version like the one in the first picture?

I tried to get one directly from Cummins from the online parts catalog, but it was unclear what exactly they had. There is extremely little descriptive information on the parts catalog system. The online system is also very clunky to use.

I just ordered a Stant thermostat off of Amazon that is supposedly what was installed at the factory. However, it looks like the one in the second picture.
There is an old thread that has a good pic of the difference in the thermostats. Notice the wider opening in post #4.

https://www.skoolie.net/forums/f39/5...ace-12530.html

The local O'Reilly's has a thermostat that has the wide open thermostat but has a different base(?) than the Cummins 3946849 that Booyah has referenced.
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Old 07-01-2020, 03:46 PM   #15
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Thanks for all the great information everybody. I've got a brand new thermostat on the way with the 3946849 part number.

Funny enough, I work for Cummins (but I have nothing to do with making engines) and I live in Columbus, IN (Cummins Headquarters), and have Cummins engineers for neighbors, but the easiest way to get this information and the part was on the internet.
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Old 07-01-2020, 03:57 PM   #16
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Good link bamabus, I forgot all about going over this before.

In that thread where dred shows 2 thermostats. The one on the left is what you'll most likely get from parts stores, and is the one that we would have trouble with overheating. The one on the right is the 5292712 that is for newer engines.

If we used the thermostat for newer engines in the older ones, we'd run hotter then normal, but it wouldn't overheat/boil over. Running the small hole thermostat would overheat/boil over. When we installed the correct thermostat #3946849 those issues went away.
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Old 07-01-2020, 04:08 PM   #17
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Quote:
Originally Posted by Ourversionoflife3 View Post
Thanks for all the great information everybody. I've got a brand new thermostat on the way with the 3946849 part number.

Funny enough, I work for Cummins (but I have nothing to do with making engines) and I live in Columbus, IN (Cummins Headquarters), and have Cummins engineers for neighbors, but the easiest way to get this information and the part was on the internet.
That doesn't surprise me. I wasted my time for a week calling other mechanics, parts clerks, sales reps, and even a few engineers.

The one engineer I talked to tried to tell me the smaller hole from the thermostat would increase the velocity, and doing that would increase the cooling capacity . He told me the new thermostat wasn't an issue and that we had issues with the radiator. That was funny to me because we replaced the original thermostat because it was hung open and ran cool. I asked him to explain how a thermostat change would take a bus that was running too cool to overheating and that was his response.

So what do you do for cummins?
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Old 07-13-2020, 01:33 PM   #18
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I had the same issue. I replaced everything like thermostat, coolant. Once i added the TRANSMISSION cooler i was no longer flowing HOT transmission fluid to the radiator. The temp is 185-190 always. Like a new car. The needle doesn't move. I never think about the temp anymore. The original radiator fan NEVER comes on.






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