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Discussion Starter #1
Recently blew a hose coming out of the heater core, pulled over immediately and shut it down. Roadside service towed the truck to a shop (leaving it outside in the parking lot) instead of back to my house like I had requested. Overnight temps were down to 12 degrees, when I received the truck back the following afternoon, I found that the radiator and lower hose were frozen solid. (Thus my reasons for wanting it towed to my house so that I could keep it out of freezing weather and plug the block heater in....and do the repairs that night).

I replaced the radiator, thermostat, rad cap (13 lbs), new hose to replace the exploded one and fresh coolant. I bled the air out using one of these things


After 5 days of driving, the overflow tank is full but the truck had consumed nearly 3/4 gallon of coolant. Nothing seems to be leaking. The temp gauge has been a little nutty the last few months (suddenly dropping down to being cold, then jumping back up) besides replacing the ECT sensor, any other ideas of what it could be?

Oil was just changed as well and no milkshake (I'm assuming we can rule out head gasket issues?)
 

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Discussion Starter #2
side note: Insurance company is asking for a written estimate for repairs/diagnostic before they'll consider a damage/negligence claim against the towing company. I don't want to go through a dealership; any recommendations of independent shops in the Snohomish County, WA area that are reputable?
 

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Mambeau / Admin
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Which heater circuit hose did you blow?

Did it rupture inside the cab or inside the engine bay?

Did you turn off the heat while you were working on the hose replacement, etc.?

My first guess would be that when you refilled the system the heater core was cut out of the fluid circuit, and the missing 3/4 gallon is what it took to refill the heater components and lines once you turned on the heat and opened up that side-circuit again.
 

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Discussion Starter #4 (Edited)
Which heater circuit hose did you blow?

Did it rupture inside the cab or inside the engine bay?

Did you turn off the heat while you were working on the hose replacement, etc.?

My first guess would be that when you refilled the system the heater core was cut out of the fluid circuit, and the missing 3/4 gallon is what it took to refill the heater components and lines once you turned on the heat and opened up that side-circuit again.
Enola!! Just who I was hoping to hear from!!

The rupture occurred in the engine bay (the u-shaped hose that runs from the top/rear of the engine block, through the HVAC mechanical valve, and connects to the heater core (I believe).

When I refilled and purged the cooling system, I ran the engine with climate control set to hot, flowing fresh air (not recirculate) and fan blowing on Hi.

Photos of the blown hose and location on the motor.

In both cases (I refilled a little bit more this morning) the overflow reservoir was full)
 

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Mambeau / Admin
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Which coolant temp sensor did you replace? The one up front (engine coolant temp sensor for the ECM) or the one on the side under the manifold (engine coolant temp sender for the temp gauge in the cluster)?

I don't know whether the temp gauge wackiness is related to the coolant problem, but I'd like to be able to rule it out.

The split in the old hose is consistent with excessive pressure. It's not a sure-fire pointer to overpressure, but overpressure is still a possibility.

That, combined with the mystery of the missing coolant, makes me wonder whether there's an obstruction or blockage somewhere.
 

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Mambeau / Admin
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If I recall correctly, there's a drain line or tube that runs from somewhere on the bottom of the HVAC enclosure through the firewall. I've never been sure exactly where the open / outlet end is. It should be low / underneath in the vicinity of the firewall.

This is supposed to be for draining condensation from the A/C unit, but I suppose it might also serve as an outlet for coolant leaking out of the heater unit.

I'd recommend locating the open end of this drain tube and checking to see if there are signs of fresh coolant there.

I've got a sneaky feeling the heater unit is involved - either as a cause for the original hose rupture or something that maybe cracked / ruptured when parked overnight with the busted hose allowing sub-freezing air to get to it.
 

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Discussion Starter #7
If I recall correctly, there's a drain line or tube that runs from somewhere on the bottom of the HVAC enclosure through the firewall. I've never been sure exactly where the open / outlet end is. It should be low / underneath in the vicinity of the firewall.

This is supposed to be for draining condensation from the A/C unit, but I suppose it might also serve as an outlet for coolant leaking out of the heater unit.

I'd recommend locating the open end of this drain tube and checking to see if there are signs of fresh coolant there.

I've got a sneaky feeling the heater unit is involved - either as a cause for the original hose rupture or something that maybe cracked / ruptured when parked overnight with the busted hose allowing sub-freezing air to get to it.
Enola,
We might be getting somewhere here. The truck has A/C in it but the A/C Compressor is out (I think the expansion valve O-ring went and I haven't taken the dash apart to get to it). Do you have a schematic of where the drain hose might be? Can I get your opinion if using the UV dye and black light would be helpful at all?

I an inclined to agree with you that the heater core may have been cracked during the freezing temperatures as well and could be leaking out from there too. Would this explain why the cooling system is not pulling coolant in from the overflow tank?
 

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Mambeau / Admin
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Hmmmmm ...

The A/C compressor being removed might have something to do with it, but I'm at a loss to figure out how.

The drain hose or tube I mentioned is one of those mystery parts that isn't illustrated on components diagrams or parts listings. It's associated with the A/C cooler unit, and it's listed as a Cooler Unit Drain Hose.

My understanding is that it comes off either the A/C cooling unit or the HVAC casing and leads downward through the firewall or floor.

It's one of those things that gets mentioned every few years, and it's been a very long time since I've had to even think about it at all.

I'm only guessing it's possible that a major leak from the heating unit might drain out from the cooling drain hose. I don't recall anyone having trouble with the drain hose except when it gets clogged and the excess water (usually from A/C condensation) builds up and floods the floor.

I don't know if your mention of UV and dye meant using it in the A/C circuit or the coolant / heater circuit. If you meant the A/C circuit, I'm not sure how that would help at all.

Are you sure you got the cooling system fully cleared of air? The fact that coolant is disappearing from the radiator but not the overflow tank is very suspicious. Air in the system might explain it.

So would a blockage or obstruction of some kind. I'm still wrapped up with the major slit in the busted hose and the notion it looks like a failure from overpressure.

Are you sure you're getting flow / circulation through the cooling system? Are you sure the new thermostat is opening correctly?

Does your Taco have a factory Towing Package? If so, there's a mini-radiator for the auto transmission built into(?) the main radiator.
 

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Discussion Starter #9 (Edited)
Enola, I topped off this morning and checked it again when I got home. The oil filter cap has some condensation in it but I drive about 10 freeway miles to work and home (20 miles round trip) and in the Seattle area, we've been down in the teens/20's with snow. From what I've read, this is not exactly uncommon.

I drained the oil pan and the 10W30 AmsOil, that I just did the change, was obviously dirty but there did not appear to be water in it. I pulled the filter and it did not show signs of milkshake either. I needed to get to work this morning so I tossed in some 0W40 Mobil 1 full synthetic that I had in the garage.

I topped off about 1/8 gallon of coolant, drove with full heat on hi to work and parked on a decent incline in the parking lot with the front end facing up-hill.

Third picture is a better very of the hose that ruptured and the location on the engine. You can see the brand new one that replaced it.
 

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Discussion Starter #10
Enola,
With regard to the UV Dye, I was talking about using the UV Dye that goes into the coolant to see if I can identify where anything may be leaking externally. Thoughts?
 

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Mambeau / Admin
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I guess it can't hurt to try the dye and see if you can find a leak.
 

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Discussion Starter #13
How could the heater core be cracked? Can a heater repair shop fix this?
My initial thoughts are that it's a cracked head. the cooling system is under pressure until it cools down. Oil system is under pressure until you turn the engine off and it's no longer pumping. Coolant is not contaminated with oil, but the oil is contaminated with coolant. I'm thinking that the pressurized coolant is getting into the oil through a crack in something....either the engine block (I'm ****ed) or a cracked head (sucks, but not the end of the world). I'd be happy if all it was was a blown head gasket but I think with aluminum heads that those cracked when the water froze instead of the cast iron block.
 
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