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Discussion Starter #41
when you say you replaced the overflow tank hose......do you mean the one that goes from the upper hose cap housing to the tank?


i already replaced with a MOPAR thermostat when i replaced the leaking water pump. at that time, i also used the prestone flush kit & flushed the system. i did that less than a month ago.
 

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I have been dealing with the same issue with my '03 4.7 Dakota QC. Engine runs perfect, plugs are clean, no sweet smelling exhaust, so it's not the head gaskets. No matter what I replace, coolant goes into the reservoir but won't go the other way when the engine cools. When I loosen the new Mopar radiator cap I even hear a vacuum. The only thing I haven't replaced is the hose between the reservoir and the fitting under the cap. I need to figure out the size of that hose. Is there anything inside the reservoir that can prevent flow the other way? As long as I keep checking the coolant level at the cap, and adding coolant at the cap, it does not overheat.
 

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Discussion Starter #43
yup. alpinegreenneon, you sound like the exact situation that i'm having.

just go my truck back from the shop. they said they can not reproduce the problem. they said they tested the radiator cap & it is working as it should. they topped off the coolant and "bled" the system and it is fine. no problems found. they want me to drive it around until it does it again, and then they can check it again. thing is, i know it will happen again (b/c it always does) and then the same thing will happen & they will not be able to find anything.

it's just getting frustrating b/c no one knows what's going on. i almost wish it was the head gasket b/c then i can at least know why this is happening.
 

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I have been dealing with the same issue with my '03 4.7 Dakota QC. Engine runs perfect, plugs are clean, no sweet smelling exhaust, so it's not the head gaskets. No matter what I replace, coolant goes into the reservoir but won't go the other way when the engine cools. When I loosen the new Mopar radiator cap I even hear a vacuum. The only thing I haven't replaced is the hose between the reservoir and the fitting under the cap. I need to figure out the size of that hose. Is there anything inside the reservoir that can prevent flow the other way? As long as I keep checking the coolant level at the cap, and adding coolant at the cap, it does not overheat.
IIRC it's 5/16 ID, I replaced mine with some from O'Reilly. If that is leaking it would pull air vs. coolant and as cheap as it is (something like $3 for a couple of feet) it'd be worth paying that to eliminate the component from the problem.
 

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Yeah, you have a head gasket leak. Maybe a cracked head. How do I know? Because the symptoms are exactly what I experienced with my 2002 Dakota 4.7.

Let me ask you, have you ever driven your truck when it was overheated? That's death to 4.7s. In my case, the P.O. had driven it hot on a couple of occasions and apparently that was enough. Thing is, it's difficult to diagnose because as long as the coolant level is up it'll be fine, but as soon as it burns off enough coolant the temperature will start to rise. Meantime, as long as there's any coolant at all in it, the overflow tank will remain full when cold.

Solution? Well, the cheap one is to keep slopping coolant in it, and the expensive one is to re & re the heads and possibly the whole engine, depending on whether coolant has found its way into the crankcase.
 

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"If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck"

You have cylinder pressure entering the cooling system.
The longer you keep not fixing it, the more damage you will have to deal with.
If you are getting coolant into a cylinder, you are damaging the top of the cylinder wall too.

This is the difference between just top end work and a rebore.
 

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Discussion Starter #47
Thing is, it's difficult to diagnose because as long as the coolant level is up it'll be fine, but as soon as it burns off enough coolant the temperature will start to rise. Meantime, as long as there's any coolant at all in it, the overflow tank will remain full when cold.

thing is with mine, it's not burning off. i'm not getting any smoke from the tail pipe & the level is fine until it gets pushed out of the overflow tube. otherwise everything is fine. the level is good until it gets pushed out (not burned up). and the last shop it was at didn't get any hydrocarbon reading in the coolant, so they said they did not want to condemn the head gasket.
 

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...... otherwise everything is fine.
except it is not fine. It is blowing coolant out. BLOWING coolant.

I understand you do not want to pull the heads and spend the money. I do.
I understand that the forum is giving you reasons to come up with other theories.

If you want to limp along for a while more.
Take the thermostat out.
Get a radiator cap with the pressure release switch on it, and leave the switch up.

It might stop losing coolant because you will have full flow and a path for air to escape.

My money is two headgasket fractures from two adjacent cylinders into the coolant passage between them, rather than a direct cylinder to cylinder failure.

I have been through this. Good luck with it.
 

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Discussion Starter #49
thank you for the tip. i don't want to put money into it b/c it's on it's last leg. possible trans issues, and it has just about 250k miles on it. i actually tried to get an estimate from a couple local shops about what it would cost to do the head gaskets, but they both wouldn't touch it.

so that's when i brought it to the other shop to for them to use the blue devil head gasket repair fluid. but when they checked it, they told me about the test they did & couldn't condemn the head gasket.

My money is two headgasket fractures from two adjacent cylinders into the coolant passage between them, rather than a direct cylinder to cylinder failure.
if this could be the case, do you think that using something like the blue devil product would even help?
 

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I do not know anything about the Blue Devil "headgasket repair fluid"
I have no comment on it.
 

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Using blue devil is kind of a (very) temporary fix at best and very well could result in more damage. Honestly with the 4.7 if you have a head gasket failure it's better to get it fixed sooner than later when it'll cost a lot more. It's pretty easy to check for a blown head gasket, leave the rad cap off and if it blows coolant out of the mouth on starting you have a major leak. If it doesn't then move onto a compression test or if you have the inclination a leakdown test would be even better.

Given everything else that's been done and checked that's about the only thing left.
 

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I'm afraid I agree with Kevin. I've been to this movie before. If, as you say, the truck is approaching the end of its useful life, you should probably reconsider option 'A' -- just keep slopping coolant into it. You'd be surprised how long it can go like that as long as you don't let it run low and overheat.

Best of luck.
 

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With my situation, the coolant only goes into the reservoir. I use a mityvac to suck out excess coolant to keep the level in the reservoir from going too high so I don't actually waste coolant. What I suck out goes back under the radiator cap. I just did a 700 mile trip. It did not overheat at all. I transferred 24 ounces from the reservoir back into the system to get it full under the radiator cap. The engine oil has no coolant nor does the trans fluid. Short trips into town and back, about 40 miles I transfer maybe 3 ounces at the most.
The one time and only time it came close to overheating was back in May. I shut the engine off immediately and had the truck towed home. Since that time, i have just been making sure the coolant level under the cap stays full. The new radiator cap is a Mopar. The new water pump is a Delco with the cast iron vanes. The tensioner and belt are Gates. I only use the Mopar HOAT coolant diluted 50% with distilled water.
 

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Alpinegreenneon - I will lay dollars to donuts that your tube to the overflow tank isn't sealing proper, so when it would normally suck the water back in, it's sucking air in.

I'd check both ends to make sure that you have a good seal and that it's snug and tight.

If EITHER end slides on and off easily, it'll do what you're describing - push it into the overflow tank, then not pull it back.

(So will some other leaks that take pressure well, but do not take vacuum - one way leaks that will sooner or later get worse.)

RwP
 

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I know this has been getting really confusing and you're getting conflicting info. On one side you're being told that you've got a blown head gasket, on the other, you're being told that you don't and pressure tests have confirmed this. With everything you've tried, it's the only thing you haven't visually confirmed, because it requiters pulling the heads. You have another reason to pull those heads. At 250K, your engine can use either an overhaul or at least freshening up. So if you pull the heads, it wouldn't be just for the gaskets. You may want to look into a rebuild or a swap for an engine with less miles. You're only other option is to keep running this engine till it dies. If you take this route, pull out the thermostat and leave it out.

Ed
 

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Discussion Starter #57
Alpinegreenneon, my truck is the same way. as long as the level is good (by the cap) i have no issues. i drove it from Baltimore, MD to Myrtle Beach earlier this year with no issues at all. i just made sure the coolant was topped off before leaving for the drive home and it was good to go. maybe i will get a hand pump and transfer the coolant back from the overflow to the cap.

RalphP, does it really create a seal at the overflow? the cap for the overflow is just a pop top type thing, so there isn't a seal created there....is it?


and thank you all for your input. i really appreciate the comments. it helps me look at other things and at least understand what could be going on.
 

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Discussion Starter #58
RXT, thank you. but pulling the thermostat will not give me any heat, right? if it were just me in the truck, i think i could deal with it. but i pick up my kids after i get off work. and with winter coming here in Baltimore, i can't really have that as an option.

i think i'm just going to have to keep an eye on the level, and do like Alpinegreenneon does & take the excess coolant from the overflow and "recycle" it back into the system.
 

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Pulling the thermostat won't affect heat….. However, if the engine is cold, it will take longer for the heat to warm the interior or defrost the windshield, until the engine warms up. Once the engine is warmed up, heat will work as before. If you want heat first thing in the morning, allow the engine to warm up for a few minutes. For really cold days, you may consider a winter blanket over the rad to let the engine warm faster.

Ed
 

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RalphP, does it really create a seal at the overflow? the cap for the overflow is just a pop top type thing, so there isn't a seal created there....is it?
Air flows easier than water, so if the hose from the radiator neck to the overflow tank isn't air tight, it'll pull the air back, not the water.

It's not the same kind of pressure seal you're thinking of. Also, the TANK isn't sealed ... it's just that any pin hole that allows air in will let it suck air back in, even if it's a tight enough seal that the coolant won't leak OUT (and leak is a good term; again, it's not under pressure.)

So yes, it needs to be snug, but if the hose is sized properly and the fittings are barbed, you won't need but just a tight push-on seal.

(That's what I ended up doing; going one size smaller on the hose, lubricating the fitting on my radiator which, alas, wasn't barbed, and using a brass barbed coupler upstream to the next larger size to fit the tank. So far so good, as long as I check it.)

RwP
 
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