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Old 11-15-2019, 10:08 AM   #1
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C7 Coolant Temp: Low at Idle in Cold Weather

I had nice heat in the bus on my trip home from Colorado, but as soon as I got to Wisconsin and let the truck idle I noticed that it could not keep the coolant warm enough to provide any use for heat for the interior of the bus. When I was running on the highway the coolant temperature looked to be Around 200į F, but at idle it dropped to about 140į And the bus quickly got cold. The outdoor temperature was about 25įF. I noticed the same thing on another bus with similar specs. In that case I was driving and pulled over to take a nap and shortly the bus was not producing enough heat. So how do you defrost windows If your bus wonít produce heat until itís barreling down the interstate? Reminds me of when I had a bad thermostat in my Toyota.
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Old 11-15-2019, 10:20 AM   #2
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Even with the thermostat closed, there is still some coolant circulation. In cold weather that can be enough to keep the coolant from reaching desired temperature.

I am sure that you have probably seen semi trucks with a zippered cover over the grill? That is to reduce air flow through the radiator and allow the coolant to reach operating temperature.

I have something similar on my truck just a little lower tech. It came from Amazon

If you look through the grill over my truck you can still see the Amazon logo on the cardboard box
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Old 11-15-2019, 10:38 AM   #3
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Quote:
Originally Posted by wrenchtech View Post
I had nice heat in the bus on my trip home from Colorado, but as soon as I got to Wisconsin and let the truck idle I noticed that it could not keep the coolant warm enough to provide any use for heat for the interior of the bus. When I was running on the highway the coolant temperature looked to be Around 200į F, but at idle it dropped to about 140į And the bus quickly got cold. The outdoor temperature was about 25įF. I noticed the same thing on another bus with similar specs. In that case I was driving and pulled over to take a nap and shortly the bus was not producing enough heat. So how do you defrost windows If your bus wonít produce heat until itís barreling down the interstate? Reminds me of when I had a bad thermostat in my Toyota.
That's normal especially for a pusher bus where the coolant loop has to travel all the way to the front of the bus. I would imagine the back half of the bus stays warmer than the front.
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Old 11-15-2019, 11:27 AM   #4
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Originally Posted by PNW_Steve View Post
Even with the thermostat closed, there is still some coolant circulation. In cold weather that can be enough to keep the coolant from reaching desired temperature.

I am sure that you have probably seen semi trucks with a zippered cover over the grill? That is to reduce air flow through the radiator and allow the coolant to reach operating temperature.

I have something similar on my truck just a little lower tech. It came from Amazon

If you look through the grill over my truck you can still see the Amazon logo on the cardboard box

Sure, I’m familiar with what you’re talking about. Commonly called a “winter front”, but that is something that I normally associate with old old trucks. What I’ve got going on can’t be right. I won’t be able to defrost my windshield to see where I’m going at this rate. I know everything else is working because when I’m going down the road I have to turn the heat down, because at least by the driver it gets plenty of heat.
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Old 11-15-2019, 11:41 AM   #5
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That's normal especially for a pusher bus where the coolant loop has to travel all the way to the front of the bus. I would imagine the back half of the bus stays warmer than the front.
On the bus I started working on last month, the passenger heater, heat exchangers were plugged up with dust and debris and the fins were bent over by student athlete vandals.
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Old 11-15-2019, 12:06 PM   #6
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My C7 never got over 140 on the 2800 miles home from the PNW. Only once could I get it to rise on a mountain pass. Had plenty of heat though.
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Old 11-15-2019, 01:12 PM   #7
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Sure, Iím familiar with what youíre talking about. Commonly called a ďwinter frontĒ, but that is something that I normally associate with old old trucks. What Iíve got going on canít be right. I wonít be able to defrost my windshield to see where Iím going at this rate. I know everything else is working because when Iím going down the road I have to turn the heat down, because at least by the driver it gets plenty of heat.
My 3126 (dog nose) has a set of snaps all around the front grille opening indicating that a cover can be used to block off air flow. At 2003 I wouldn't call it an "old, old truck".

If you have an IR gun (cheap at habor freight) see what the temps are going in and out of the heater core.

does your defroster seem to be blowing enough air?
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Old 11-15-2019, 01:13 PM   #8
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That's normal especially for a pusher bus where the coolant loop has to travel all the way to the front of the bus. I would imagine the back half of the bus stays warmer than the front.
Works just the same in my Dodge pickup. It's cold enough here today that if I don't block a good portion of the radiator I will not come up to proper operating temperature.

I still see semi's up here with the "winter front" on them them this time of year.
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Old 11-15-2019, 01:25 PM   #9
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At idle the coolant temps will drop off. My bus has a high idle switch that bumps up the idle to 1100 rpm or so. Winter fronts can do a nice job of keeping a warm temp at road speed, but you also run the risk of overheating if you do not keep watch on the temp.

OP, Thomas should be able to put one in your bus fairly easily.
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Old 11-15-2019, 01:28 PM   #10
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Quote:
Originally Posted by wrenchtech View Post
I had nice heat in the bus on my trip home from Colorado, but as soon as I got to Wisconsin and let the truck idle I noticed that it could not keep the coolant warm enough to provide any use for heat for the interior of the bus. When I was running on the highway the coolant temperature looked to be Around 200į F, but at idle it dropped to about 140į And the bus quickly got cold. The outdoor temperature was about 25įF. I noticed the same thing on another bus with similar specs. In that case I was driving and pulled over to take a nap and shortly the bus was not producing enough heat. So how do you defrost windows If your bus wonít produce heat until itís barreling down the interstate? Reminds me of when I had a bad thermostat in my Toyota.
HIgh idle.
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Old 11-15-2019, 01:46 PM   #11
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HIgh idle.
Believe me, I know about high idle and I even drove 7 miles at about 50 miles an hour after sitting for about an hour, and that still didnít bring the temperature up much.
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Old 11-15-2019, 02:04 PM   #12
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... hallelujah! Itís going to be 10į warmer today than yesterday. Maybe it will make a difference. The high was 25 yesterday going to be maybe 37 today. A veritable Wisconsin heat wave!
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Old 11-15-2019, 02:05 PM   #13
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Its 70 out. I had to wear a sweater today lol.
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Old 11-15-2019, 03:20 PM   #14
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I kept a big piece of cardboard for my T444E bus when the temps got below 50 or so. If you're not working these engines, they aren't making much heat, and a constant flow of cold air will in fact keep them well below normal operating temperature. Call it redneck if you want but it's reality.
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Old 11-15-2019, 05:35 PM   #15
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With all the heaters in the bus running, You'll struggle to get the engine warmed up. It just won't happen with the ambient temp below freezing, low engine load, and the heat energy you're pulling by having all the heaters on.

You can block off the grill to get it to heat up faster while going down the road. But at low idle, the engine just isn't making enough heat. If you're running into issues with the defroster working, turn off the passenger heaters and the driver's floor heater, so that only the defroster is running.

Some buses have air operated shutters on the radiator that will open and close based off of coolant temp.
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Old 11-16-2019, 12:15 AM   #16
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Lots of good information from these posts. I might try to find something to block the radiator airflow temporarily while the bus is warming up or while itís sitting still. I also have the option to shut off the valves for the coolant loop that feeds the heaters
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Old 11-16-2019, 08:51 AM   #17
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my DEV bus has air shutters... shutters closed and T-stat closed my Top radiator Hose will be pretty much cold if I let the bus idle for about an hour with the heasters inside on.. my temp gaige goes down to just off the 'C'. the DTA360 cant make as much heat as the heater cores are requesting..



my red bus auto-idles itsself up and down to maintain 165-170 coolant temperature.. it will go as high as 1450 and down to normal at 700.. it varies on its own when I have the Idle porogrammed in the computer to 'Auto'


-Christopher
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Old 11-16-2019, 01:18 PM   #18
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Lots of good information from these posts. I might try to find something to block the radiator airflow temporarily while the bus is warming up or while itís sitting still. I also have the option to shut off the valves for the coolant loop that feeds the heaters
Covering the radiator while stationary won't do anything. It blocks the air being forced into the rad at speed.
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Old 11-17-2019, 11:36 PM   #19
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Diesel engines don’t produce much heat at idle, compared to gas engines which stay nice and toasty. Under load of course diesels do much better. Most solutions have been covered in this but I suggest checking the heater hose valves at both ends to make sure they’re open all the way and turn on the coolant pump.

Also if the defroster is brining in outside air you might consider turning the fan down to medium speed instead of high speed. Depending on the situation, high speed fan brings in a higher volume of cold air and cools the heater core where as a medium fan may still cool the heater core but not bring in more than needed cold air.

I could never understand the cardboard box on the radiator thing though. If the engine temperature is below 180 or whatever the thermostat is set to then there won’t be any coolant flowing through it anyway so the box isn’t helping. If it’s above around 180 then the heater should be plenty warm... anyway if it works then why not I guess...
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Old 11-18-2019, 08:09 AM   #20
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Diesel engines donít produce much heat at idle, compared to gas engines which stay nice and toasty. Under load of course diesels do much better. Most solutions have been covered in this but I suggest checking the heater hose valves at both ends to make sure theyíre open all the way and turn on the coolant pump.

Also if the defroster is brining in outside air you might consider turning the fan down to medium speed instead of high speed. Depending on the situation, high speed fan brings in a higher volume of cold air and cools the heater core where as a medium fan may still cool the heater core but not bring in more than needed cold air.

I could never understand the cardboard box on the radiator thing though. If the engine temperature is below 180 or whatever the thermostat is set to then there wonít be any coolant flowing through it anyway so the box isnít helping. If itís above around 180 then the heater should be plenty warm... anyway if it works then why not I guess...

the cardboard or Air shutters allow the radiator to be a "ballast" or "heat storage" if you will.. the engine temperatiure can be allowed to rise above thermostat temp when driving at higher engine loads.. (not idle or slow n go).. so say the engine Tstat is 190 and you make 200.. then when you stop and idle you have the coolant in the radiator to use for extracting heat from if the fan is off and radiator mostly covered.. this really works best if you have Horton electric fan clutches as your fan can truly be shut-down 100% as opposed to viscous clutches whuch usually have a 200-300 RPM minimum and will blow your heat away..
-Christopher
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