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Old 05-27-2016, 04:17 PM   #1
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1996 DT466 Thermostat Issue!

Hey Everybody, My 1996 Int 3800 (DT466 mechanical) is failing to circulate coolant through to the heat exchangers so I'm figuring I have a bad thermostat.

I ordered a replacement only to find that the thermostat on the top of the engine (radiator hose coming out of engine block) is completely different.

Is there another thermostat somewhere else in addition to the one in the thermostat housing on top of the engine?

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Old 05-27-2016, 05:02 PM   #2
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Originally Posted by sickrunvanyardsale View Post
My 1996 Int 3800 (DT466 mechanical) is failing to circulate coolant through to the heat exchangers so I'm figuring I have a bad thermostat.
I guess maybe rephrase your question? Are you saying you dont have any heat going to the heaters inside the bus?
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Old 05-27-2016, 05:06 PM   #3
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I guess maybe rephrase your question? Are you saying you dont have any heat going to the heaters inside the bus?
Yeah, that's about the size of it right there. Nothing coming into the front and nothing going to the rear. All valves are open.
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Old 05-27-2016, 05:09 PM   #4
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Meh...that doesnt sound right. Engine operating temperature ok? Is this a new bus to you? Have you had hot water to the heaters before? If not, are you SURE you arent missing a valve? Low on coolant?
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Old 05-27-2016, 05:19 PM   #5
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I've had the bus for a few years now. All valves are open and coolant level is good to go. I'd "heard" that if the thermostat in the DT466 fails "closed", than coolant won't circulate to the heater cores. I can't verify this but after taking her out for a spin, the engine is definitely up to temp but it seems that coolant isn't circulating back to the heater cores. This is why I thought the thermostat was failed shut.
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Old 05-27-2016, 05:32 PM   #6
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Got it. That fine of a detail for a DT is too many years behind me to remember.

Someone will chime in, I just thought I'd answer while others pondered.

However, I would think if I thermostat was stuck closed, you'd have engine overheat issues.
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Old 05-27-2016, 05:47 PM   #7
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Got it. That fine of a detail for a DT is too many years behind me to remember.

Someone will chime in, I just thought I'd answer while others pondered.

However, I would think if I thermostat was stuck closed, you'd have engine overheat issues.
I thought that as well so I haven't pushed it much. I figured the DT466 on short trips would at least get to temperature without overheating with a closed thermostat. I'm stumped. I tested the thermostat located in the t stat housing (top of engine, large diameter rad hose attached). It opens at around 180-185 degrees F. I'm wondering if there's another thermostat housing somewhere near the oil cooler?
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Old 05-27-2016, 06:01 PM   #8
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does that bus have a boost pump for the heaters? ive seen before where those pumps stop at a point where they refuse to allow flow.. try turning that pump on if you have one...

-Christopher
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Old 05-27-2016, 06:13 PM   #9
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Is there not a 1" or so line coming off the top of the radiator tank? That should bypass the thermostat and go to the heaters....if I recall.
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Old 05-27-2016, 07:21 PM   #10
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Did you check the valves that might be closed? Many schools shut them off when it gets warmer to keep from heating up the bus on the inside.
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Old 07-06-2016, 03:39 PM   #11
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Sorry for the lack of followup on my part, I've been busier than I want to be and Alaskan summers are short so time spent outdoors is fleeting!

Quote:
Originally Posted by cadillackid View Post
does that bus have a boost pump for the heaters? ive seen before where those pumps stop at a point where they refuse to allow flow.. try turning that pump on if you have one...

-Christopher
There's no booster pump on this model.

Quote:
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Is there not a 1" or so line coming off the top of the radiator tank? That should bypass the thermostat and go to the heaters....if I recall.
I don't think so.

IMG_1320 by SickRun VanYardsale, on Flickr

Quote:
Originally Posted by crazycal View Post
Did you check the valves that might be closed? Many schools shut them off when it gets warmer to keep from heating up the bus on the inside.
There's one valve conveniently located in the cockpit right next to clutch pedal by the front heater core.
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Old 07-06-2016, 03:58 PM   #12
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Another update to the temperature issue. I pulled the thermostat off the top of the engine and suspended it in hot water. I heated it up to ~190 and it opened up and remained open no problems. I changed out the coolant filter, topped off the coolant, reinstalled the thermostat and took her out for 95 mile run up the highway. The skoolie pulled up Thompson Pass in fourth gear at about 25-35 mph. The Pass was a pretty good test being that it's a pretty significant grade and rises from sea level to about 2600 feet in a few miles. It didn't overheat and didn't appear to go over 210 on the stock temp gauge.

About a week or so later, we drove from Valdez to Fairbanks (350 mile trip) and never had an issue. I ran it with the heater valve open and the temp gauge never rose past the halfway mark between 200 and 210 on the stock gauge. It was in the eighties up in Fairbanks so I decided to shut the valve to save myself from overheating. The unit ran *a little* warmer with the valve shut but nothing too drastic to cause concern.

On the return trip we made it about 3/4 of the way back and stopped for fuel. On the way out of the fuel depot I noticed that the temp was sitting at 210 on the stock gauge. This was an abnormal condition seeing as how this was never an issue in much warmer and tougher driving conditions. I pulled over and let the engine idle for a while with no change in temperature on the gauge. I opened the engine cover and notice some coolant had come out of the cap (i'm assuming).
IMG_1319 by SickRun VanYardsale, on Flickr
I used my handy IR thermometer and nothing on water pump housing, thermostat housing (top of engine) or radiator exceeded 185 degrees. I removed the surge tank cap slowly and there was no pressure beneath the cap. I thought this was abnormal. We drove the rest of the way home and the temperature gauge never moved from where it was. The fan clutch is operational as I could hear it kicking on and off during our trip.
IMG_1323 by SickRun VanYardsale, on Flickr
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Old 07-06-2016, 04:48 PM   #13
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what kind of fan is on that rig? is it a viscous clutch fan or an air actuated fan clutch?

I recently replaced the fan clutch on my DT-360 (the 466 smaller cousin).. because my temp would approach 212 and my fan would not spin very fast....

if its a viscous clutch and your bus is the type where 1/2 of the grill opening is the radiator and 1/2 is the turbo cooler.. many people install the incorrect fan clutch that will never properly activate...

-Christopher
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Old 07-20-2016, 12:33 AM   #14
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It's the viscous clutch design with the 1/2 radiator, 1/2 intercooler setup in the grill. The clutch "appears" to operate properly. I can hear it kick on and off during normal operations and it kicks on and stays on when the engine is hot.
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Old 07-20-2016, 06:53 AM   #15
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the fact a viscous clutch runs up and stays on ..(if its truly viscous clutch).. says that you are moving Hot air from the radiator... as it measures the AIR temperature from the radiator...

is it possible the air-shutters are closing on you (if you have them)... or the radiator air flow is not good?

if you have poor coolant circulation usually a viscous clutch will never fully run up... (an air clutch would run continuously)..

whats interesting is even in 96 degree heat my viscous clutch runs up for maybe a minute or so at a time and then slowly backs down.. they dont "kick" per say.. you';ll hear a slow run up to a roar in the fan... then a slow run down from the roar when it slows down...

-Christopher
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Old 07-20-2016, 08:48 AM   #16
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Quote:
Originally Posted by sickrunvanyardsale View Post
There's one valve conveniently located in the cockpit right next to clutch pedal by the front heater core.
Only one valve? That's not nearly enough! My bus has 3 to control the coolant flow to the heaters. One by the driver's left foot and two by the frame rail to the right of the engine. All 3 need to be open to operate the heaters. The valve by the driver is the only one that needs to be closed to turn off flow to the heaters. The other 2 are used to keep coolant in the heater cores and lines while a mechanic is working on the coolant system, I suspect.
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Old 07-20-2016, 11:16 AM   #17
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3 heater valves.. The 2 under the hood are the mains.. Turning those off will turn off all coolant flow to the heater cores and also isolate the coolant in those lines . So for instance if the system needed a water pump or a hose under the hood closing those valves makes it so you don't have to drain the heater cores down.. And vice versa. A leak in a heater core in the bus could be isolated with these valves.

The valve by the driver foot controls heater flow to the heaters on the left side of the bus.. Typically the left defrost, left driver heat, left first seat heat, left mid heat and left rear heat..

Closing the driver valve only and leaving 2 under hood open allows the right front heater cores by the door for right defrost and right well heat to still get hot....
Summer position is typically all 3 closed..
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Old 07-20-2016, 11:24 AM   #18
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Ah yes. My bus would have had the same configuration when I had all the heaters installed. I removed all heaters except for the driver's side heater. Since my short bus is better insulated it is the only one necessary. It alone provides enough heat even in the dead of winter for passenger comfort and window defrost. Now I just use the one valve by the driver.
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