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I have a 2007 grand caravan with the 3.3 motor and it's being a bear to diagnose.

On Thanksgiving, the water pump failed catastrophically; silently dumped all the coolant without an overtemp warning, so I don't really know how long it was running dry for; the cabin heat was spotty for a few days before this.

We replaced the water pump and thermostat and used the dealer coolant, but it overheats when driven even a short distance, and all the coolant ends up in the overflow reservoir. With the temp gauge maxed, the cabin heat blows cold. It runs rough; with fresh plugs and wires, it sometimes issues check engine codes for misfiring.

But... there's no white smoke, no sign of oil in the coolant, and when my mechanic pressurized the cooling system, it held the pressure.

His current best guess is that the gasket blew somewhere near an exhaust port, and hot exhaust is filling the system and shoving the coolant into the overflow.

Does that make sense? What kinds of tests can be done to make sure?
 

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Make sure the thermostat is good. I had one bad out of the box one time. From then on I always checked by putting the thermostat in a pot of boiling water and making sure it opened before installing. The few 3.3 head gasket failures I have seen have all been external, meaning the coolant was allowed to leak outside of the engine at the joint between the head and block. I have seen compression/exhaust leaking into the cooling system on 2.2's. You can detect it by using a tail pipe sniffer at the radiator cap opening. The 3.3's can be difficult to bleed. Make sure you have all the air out of the system.
 

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Any coolant flow? Hoses warm?
These water pumps are very close to a frame rail and the motor mount almost has to be pried over to squeeze the pump assembly out and back in. I've seen broken plastic impellers on a replaced pump from an install that went wrong.
Compared to earlier generation 3.3L water pumps, these are a bear to get in and out.
Head gaskets usually aren't a problem on these unless severely overheated/high mileage. There is a test for exhaust gas components (CO2) in the coolant that would be from a failed head gasket or cracked head.
http://www.ehow.com/how_10026175_test-co2-car-coolant.html
 

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No heat means that there is air in the system. It may be ingesting it from a loose connection, or it may be exhaust blowing in from a cylinder that has a bad head gasket. It won't be a bad thermostat alone, if it's overheating; there would also have to be air in there to make the heat blow cold when the engine is hot.
 
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Discussion Starter #5
Thanks for all the info!

So, since there is air repeatedly getting into the system, it's almost certainly the head gasket (though we could check to verify flow and look for a leak sucking in air someplace, but that seems unlikely, and could check for CO in the coolant to make sure). A shop I just talked to said if they do the head gaskets on a motor with 155k on it, the bottom end could blow before too long, so I'd be better off just putting in a new engine. Ouch.
 

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Check under the right passenger side by the rear tire for signs of fluid. My 05 did the same thing and I couldn't figure it out I had changed the pump filled and bled the system and still had temp and fluid level issues. It turned out to be the rear heater line sprung a leak. I had to bypass it cause it has to be shipped freight and costs around 250 so the title would have been in the 500 range just for the part.
Good luck
Mick
 

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If the coolant isn't circulating, it will boil at the hot spots around the exhaust valves. This can create air pockets.
Less or more than a 50/50 antifreeze mixture either way can lower the coolant boiling point.
Inability of the system to pressurize under a good 16 lb radiator cap will also lower the boiling point.
http://www.penray.com/images/95.011.pdf
http://www.heat-transfer-fluid.com/pdf/techpapers/pressure-boiling-point.pdf
Take a sample of your boiled coolant to a garage with the CO2 (combustion gases) test kit and wait for their answer. Witness the test for yourself if they will allow it and you feel that they may not be honest with you. The test fluid color change from blue to green determines the presence of CO2. I've seen some samples almost turn yellow with very high CO2 presence.
Don't just automatically assume that the gaskets have failed yet, although it is possible that they may be leaking from the combustion chamber into the water jacket and need replacement.
 

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Make sure to check your hose clamps and make sure they're tight. If one is just a little bit loose, it can suck air into the system. Also, have you had the radiator cap tested to make sure it's holding pressure? If not, you may want to do that. I don't really think you've got a blown head gasket, I think you've got air trapped in the system. Try parking on an incline or on a set of ramps and running it without the radiator cap until it reaches operating temp. If the antifreeze is low, then top it off and see what happens.
 

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You can also try drilling a small hole, 1/16", in the outer edge of the thermostat and then re-installing the thermostat with the hole at 12:00. This will allow air/gases to bleed through the thermostat rather than building up behind it preventing it from opening. I've never had to do this on a 3.3 V6 but it works well on the 2.2 I4.
 

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Bad head gasket in no way suggests that the bottom end needs service. There's no correlation there. Don't let them scare you. Sometimes that's someone's way of buying your vehicle cheap and fixing up themselves to either get a cheap ride or flip for a profit, at your expense.
 

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bressen said:
Thanks for all the info!

So, since there is air repeatedly getting into the system, it's almost certainly the head gasket (though we could check to verify flow and look for a leak sucking in air someplace, but that seems unlikely, and could check for CO in the coolant to make sure). A shop I just talked to said if they do the head gaskets on a motor with 155k on it, the bottom end could blow before too long, so I'd be better off just putting in a new engine. Ouch.
Like Bob posted, that is just a scare tactic. A bad HG does not correlate to a bad bottom end unless it's already showing signs of failure. I'd steer clear of that shop from now on.

I'd make sure the clamps are tight, test the thermostat, replace the radiator cap and bleed all air out before condemning the head gasket. The hole in the thermostat is a good trick - usually only needed on the 2.2/2.5 4 cylinder engines - I did it with all the 2.5's I had.

The last thing I'd do is test the coolant for exhaust gases.
 

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Thanks for all the info!

So, since there is air repeatedly getting into the system, it's almost certainly the head gasket (though we could check to verify flow and look for a leak sucking in air someplace, but that seems unlikely, and could check for CO in the coolant to make sure). A shop I just talked to said if they do the head gaskets on a motor with 155k on it, the bottom end could blow before too long, so I'd be better off just putting in a new engine. Ouch.
I know it's a different engine, but I bought a Dakota with a 3.9 V6 and a "blown motor" on craigslist with 195k. It blew a heater hose and the kid kept driving it till it made it home though it blew a head gasket. Tore off both heads, cleaned everything up, put in new valve stem seals in and new head gaskets. That truck now has well over 225k. My neighbor bought it from me and drives it daily still.
 

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There can be a problem with the bottom end if coolant got into the oil/bearings after the head gasket blew.
 

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Discussion Starter #14
Did the CO2 test, bad head gasket. (After we took out the test bulb, we noticed we could actually see the bubbles of exhaust coming up the radiator neck with the cap off). I have called five shops, and three of them want to sell me an engine swap.

Price quotes, in case anyone is curious:
  • Shop #1: $3500 for a rebuilt motor with a 4 yr/40k mile parts-only (no labor) warranty
  • Shop #2: $2500 for a used motor with 80k on it, 6 months warranty, or $5500 for a rebuilt motor
  • Shop #3: $1950 for a used motor with 72k on it, 12 month/12k warranty, or $2100 with a lifetime single replacement warranty (it ever goes bad, they'll throw in another motor)
  • ebay prices are $350-$1000 plus shipping for a used motor, no rebuilds on offer for my "R" code 3.3, but an "H" code 3.3 rebuilt is $2400.
I've found two shops that are willing to do just the head gaskets; $768 and $900 quotes, though I think that's without resurfacing the heads, and neither of them mentioned that fact, I had to ask.

I'm next to Boston, if anyone has shops to recommend.
 

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Is there any coolant in the oil (milky brown/yellow)? If not, you do NOT need to replace the engine. Just do the head gasket(s).

My head gasket failed in this manner, there was no cross-contamination of oil and coolant, and I just replaced the gasket. The head was still flat and didn't need any reconditioning. I did the gasket and timing belt myself, plus new coolant, water pump and hoses, all for $200. The extra $500 to $700 you were quoted is fair for the labor on top of parts.
 

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bressen said:
I've found two shops that are willing to do just the head gaskets; $768 and $900 quotes, though I think that's without resurfacing the heads, and neither of them mentioned that fact, I had to ask.
That sounds about right for a V6 head gasket. Best to confirm if that includes resurfacing the heads and checking for straightness. I'm in Virginia so I don't know of any shops to recommend though I did live in Holliston for a short time a long time ago.

$5500 for a rebuilt engine is a bit more than I could stomach considering the van is only worth ~$1,000 more than that. I don't see the necessity of R&R the engine because of a blown head gasket.

You might PM Bob Lincoln though I think he is in Rhode Island (?) - he may still know of some decent shops.
 

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I'm in the camp that says you don't have all the air bled out of it since the water pump swap. Therefore, it keeps over heating.
 

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Head resurfacing or planing, other than prepping the surfaces for the new MLS head gaskets isn't recommended or necessary. If the CO2 test was positive, go for the head gaskets.
While the heads are off, the tech should check them for pitting/cracks. I always like to see the failure spot first to confirm that it was actually a failed gasket at the 'combustion chamber-to-water jacket' and not something more ominous. It should be visible.
 

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Ray Green said:
I'm in the camp that says you don't have all the air bled out of it since the water pump swap. Therefore, it keeps over heating.
Read his post again - head gasket IS blown:

Did the CO2 test, bad head gasket. (After we took out the test bulb, we noticed we could actually see the bubbles of exhaust coming up the radiator neck with the cap off).
I'm in southeastern MA, there's only one good shop near me that I trust for repairs. I do everything that I can myself; what I can't, the shop does.
 
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