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Old 07-12-2019, 08:51 AM   #11
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Year: 1996
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Engine: DT466
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Quote:
Originally Posted by cadillackid View Post
EGR didnt come into play on the 466E until 04/05 model years..



was the coolant added after or before your opver-temp event? coolant expands as it gets hot... and the coolant reservopire cap is designed to vent pressure in excess of the rating on the cap... 10 PSI I think on the 466E.. getting it hot enough to turn on the overheat alarm is enough you may have been venting steam / coolant from the cap.. these busses typically dont have recovery like a car so it just goes on the ground..



checking your oil.. to make sure it is still diesel engine black and not milki-ness looking is something to do... a puff of white smoke every now and then could be an injector misfiring ...


I wouldnt be ready to worry about it yet.. however I also wouldnt allow it to run up above 220 on the temp gauge either.. you do only get so many of those alarms before a liner seal will let go... by the time you get close to 215-220 you should be hearing that fan Blazing under the hood...

-Christopher
The coolant was added before the event, about a month ago. The overheat happened while towing our truck up a long grade on 1-70 west of Denver. We were asking too much of her! It went from 210 to 230 surprisingly fast, and from now on I'll be super diligent about watching the temp. We'll also drive separately in the mountains instead of towing. The fan usually kicks on at 215-ish, but I don't recall it blazing. Could be I just wasn't paying enough attention. It was spinning when I popped the hood though. The coolant in the reservoir was at a rolling boil. The overflow line doesn't go to the ground, it seems to go to the top of the radiator. We're in town today and we have no cell signal at the bus.
I think my strategy going forward is to not be TOO paranoid but to keep an eye on everything.
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Old 07-12-2019, 08:54 AM   #12
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Join Date: May 2016
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Quote:
Originally Posted by CHEESE_WAGON View Post
I re-read the thread (with a little more sleep this time). You're probably on to something about a heater line leak, however, it may well be the heater core itself, and if it is a small enough leak, it could take a long time to drop enough coolant to be noticeable. A heater core can sometimes fool you on a pressure test -- but it is not something that can be left alone without consequence. Under no circumstances should you ever smell coolant in the interior of any vehicle.

A simple way to diagnose a heater core leak is to bypass the heater core (either under the hood or inside) by using an appropriately-sized U-shaped pipe joint loop the feed hose back into the return hose to the engine without entering the core itself. Then run / drive again to see if you still smell coolant. It may take some time for the coolant smell to disappear, but if it does go away after bypassing the core, you have a bad heater core and it should be replaced ASAP.
I've shut off the heater valves behind the firewall, so we'll see how it plays out from there. That should isolate the heater core (I think?). We shouldn't be needing cab heat for awhile.
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Old 07-12-2019, 09:06 AM   #13
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You should have no white smoke. Mine got a leak on the in bus heater line at a fitting. Smoke is an indicator of a worn out piston ring, sleeve or sleeve seal. Luckily for you a in frame rebuild is inexpensive and fairly easy to do.
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Old 07-12-2019, 09:33 AM   #14
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Boiling point for plain old water is 212F. BP in a 50/50% mix with ethylene glycol is 223, versus EG's BP of 388 at 100%.
Given "safe" operating temps, I'm wondering if either there's a lean mixture, or if there mayn't be a glitch in the gauge...
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Old 07-12-2019, 10:04 AM   #15
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I have an '01 T444E and it typically runs around 180 (by the gauge) or up to around 195 if I keep it floored. So far I've not ever seen it go over 200 (I don't like engines to run that hot). The fan kicks in (rather loudly!) at around 185-190. Some fans are viscous clutch driven (as mine is) and engage smoothly over a few seconds, some are air/electric clutch driven and kick in abruptly (often with a belt chirp or brief squeal). These clutches can and do wear out, so if the fan is just *kinda* turning but not moving serious amounts of air you may want to check it. Also you may want to check the radiator itself, both the fins (because they do get full of stuff and block airflow through them) and inside (same, except it can block coolant flow). A careful pressure washing (compressed air may work too) from behind will remove a lot of crud, leaves, dirt, etc, but be mindful not to bend or damage the radiator fins.
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Old 07-12-2019, 10:24 AM   #16
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Quote:
Originally Posted by Brad_SwiftFur View Post
I have an '01 T444E and it typically runs around 180 (by the gauge) or up to around 195 if I keep it floored. So far I've not ever seen it go over 200 (I don't like engines to run that hot). The fan kicks in (rather loudly!) at around 185-190. Some fans are viscous clutch driven (as mine is) and engage smoothly over a few seconds, some are air/electric clutch driven and kick in abruptly (often with a belt chirp or brief squeal). These clutches can and do wear out, so if the fan is just *kinda* turning but not moving serious amounts of air you may want to check it. Also you may want to check the radiator itself, both the fins (because they do get full of stuff and block airflow through them) and inside (same, except it can block coolant flow). A careful pressure washing (compressed air may work too) from behind will remove a lot of crud, leaves, dirt, etc, but be mindful not to bend or damage the radiator fins.

It normally runs at 180 and I hear the fan kick on somewhere above 210 and it cools right down. I normally hear it come on, not sure I was paying attention this time though. It ran under 210 after we unhitched the truck, and only got to above 210 after some further serious mountain grades, so I pulled over and let it cool down for a while. I've never heard a belt squeal when it kicks on, but I'm not sure if it's viscous clutch or air/electric. Guess I'll look more into it when I'm back at the bus.

I'll blow out the radiator with compressed air, couldn't hurt.
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Old 07-12-2019, 01:50 PM   #17
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Quote:
Originally Posted by Drew Bru View Post
It normally runs at 180 and I hear the fan kick on somewhere above 210 and it cools right down. I normally hear it come on, not sure I was paying attention this time though. It ran under 210 after we unhitched the truck, and only got to above 210 after some further serious mountain grades, so I pulled over and let it cool down for a while. I've never heard a belt squeal when it kicks on, but I'm not sure if it's viscous clutch or air/electric. Guess I'll look more into it when I'm back at the bus.

I'll blow out the radiator with compressed air, couldn't hurt.

It probably doesn't matter which type of clutch it has, as long as it's doing the job. I believe the viscous ones - some of them anyway - can be adjusted and they tend to engage smoothly over a couple seconds. The air clutches often give a hiss of air and a rather abrupt engagement (probably more common on big trucks than school buses, but some were so equipped).


On some pushers, they may have hydraulic fans. Cheap electric fans simply won't move enough air.
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Old 07-12-2019, 01:50 PM   #18
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Originally Posted by Drew Bru View Post
I've shut off the heater valves behind the firewall, so we'll see how it plays out from there. That should isolate the heater core (I think?). We shouldn't be needing cab heat for awhile.
May or may not do it. There will still be coolant in the core, and if it doesn't have a check-valve flapper (some have this to keep it from flowing backward), hot coolant could still enter from the engine and heat the residual coolant in the core. It really is best to loop feed hose into return hose for the purposes of total isolation.

White smoke on startup is indicative of coolant somewhere in the engine that it shouldn't be... (the cylinders) which sounds like head gasket or cracked head. A leaky EGR cooler can show similar symptoms, the reason I mentioned it, but as another member said, these did not exist until around 03-04, a non-issue on a 96.

Quick reference:
Black smoke = fuel
Blue smoke = oil
White smoke = coolant / DEF discharge

Interestingly enough, I drove a Toyota for a few months with a cracked head that didn't overheat or mix fluids, and drove fine. What it did do is blow bubbles in the radiator (exhaust gases pushing through the chambers and exhaust valve bowl) and gurgle the recovery tank on shutdown once operating temperature had been reached. Otherwise, as long you kept the coolant and oil topped off, it was happy. The thermostat had been removed to prevent overpressurizing the radiator and blowing it out, so it took forever to warm up in the winter. It got me where I was going, but it wasn't a 210-hp engine moving a 12,000-lb bus, either -- it was a 110-hp engine moving a 2800-lb car.

If possible, you might check for bubbles in the coolant. If the radiator has no filler cap, perhaps checking the recovery tank may do. If bubbles are present, ESPECIALLY before the engine warms up, that's bad news. Also, I'm not sure if the DT466 crossflows coolant through the intake like most engines, but if it does, possibly a leaking intake gasket?
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Old 07-12-2019, 03:21 PM   #19
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Quote:
Originally Posted by HazMatt View Post
Boiling point for plain old water is 212F. BP in a 50/50% mix with ethylene glycol is 223, versus EG's BP of 388 at 100%.
Given "safe" operating temps, I'm wondering if either there's a lean mixture, or if there mayn't be a glitch in the gauge...
In a sealed system the boiling point is higher than normal.
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Old 07-12-2019, 06:45 PM   #20
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Quote:
Originally Posted by EastCoastCB View Post
In a sealed system the boiling point is higher than normal.
You gain 2-3* for every pound of pressure. A 16lb radiator cap will put your boiling point around 250*
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