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Discussion Starter #1
My 21 yr old son has a 2004 Rav 4 FWD, 140k. He was driving home from a trip when the engine started overheating (in cold Minnesota!), and the heater stopped putting out hot air. We took it to a repair shop and they said the head gasket was blown or the head was cracked - Estimate of $2,800. I like the shop, have them work on my cars regularly, but the body on the Rav 4 is in pretty rough shape and with the miles, didn't think it as worth the investment.
Being a hopeful guy, I thought I'd try some gasket sealant (Blue Devil).
I drained the radiator (about a gallon, it was clean), took the thermostat out, started the engine with the heater on full and tried putting in the sealant - it won't take more than a cup, Let it run for about 15 minutes, the temp gauge finally started to rise - but no heat in the car and still could not add fluid.
I know a little about engines, but don't get it why if the coolant system is low (and the thermostat is out), the engine is hot, why the system won't take fluid.
I looked at the dipstick, the oil is dark, but doesn't look like any coolant is on it. It's sitting in my garage and my son is driving my car - help!
 

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Welcome! A guess would be that after the coolant was drained and then presumably poured back in there is an air lock in the heating system, especially if not all of the coolant could be returned to the cooling system. That plus the thermostat having been removed would explain the no cabin heat situation. Suggest that you remove the radiator cap and try squeezing the radiator hoses and, if possible, the hoses which direct coolant into the heater core. If there is air trapped it should bubble up through the radiator opening. If that is situation, after the air is expelled it should be possible to add more sealant.


Was the coolant level low when the shop checked it after your son experienced the overheating engine and no cabin heat? If there is a leak the sealant may stop it, but of course that is uncertain.
 

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Discussion Starter #5
mike.s - I had though that since it wasn't the thermostat, maybe the water pump somehow stopped pushing coolant. Any easy way to check?
 

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It's common for the heater to stop working when the engine is overheating since when the coolant level gets low the heater core typically looses coolant first due to it's high location.

The sealant is worth a try but I would never add it with the heater core in the circuit since you don't want it to get plugged. If it doesn't have a flow shutoff valve I'd disconnect the hoses and add a bypass hose.

W/o a thermostat the engine won't come up to temp. I'd reinstall it since I don't believe the stop-leak works cold. Judge temp by the gauge not the heater.

To refill a cooling system you add water (I'd use straight water for this test) directly to the radiator not the overflow bottle. There's usually an air vent somewhere hear the thermostat housing. It must be opened to completely fill the system.

A good test for a bad head or head gasket is to fill the system and let the engine idle with the radiator cap off. You should see bubbles as you add water and the system is purging air but they should stop shortly. After the system is full you should be able to rev the engine w/o blowing out a lot of water. If you get Old Faithful you have a problem that sealant may not fix.

Also, a water pump failure being the issue is very unlikely. First it's simply and impeller spinning in the water not a positive displacement pump like a car's oil pump. It doesn't "push" water anymore than a fan pushes air. So if the "fan" belt is good (and the alternator is working) the water pump is working too.
 

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Discussion Starter #7
I tried adding coolant directly into the radiator - that worked, was able to get it back to regular levels. But the temp gauge still goes high and yet the heater inside is pushing cool air. And this is without any thermostat. I tried squeezing all hoses, did not seem to make a difference,


So the engine coolant gets hot - but the heater stays cool. And the engine overheats after about 20 minutes of driving. I looked inside the radiator - don't see lots of bubbles and nothing was coming out other than a little steam. It doesn't seem to be leaking any coolant.


I looked at the estimate the shop gave me to replace the head gasket and resurface the cylinder head. They said they did a hydrocarbon test and the Rav failed right away.


Should I go ahead and have the head gasket repair done ($2,800)? Or is it something else?
 

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If its anything like the 4.1 you will need a big filler to sit tightly in the radiator as the ravs heater pipes are higher than the rad cap where you fill. the extra head height of coolant usually enough to push the air out of the heater matrix. the heater gauge shouldn't go over half way, and if it does check handy things first like leaks, rad fan engaging and thermostat ok. After that start suspecting (head gasket if cooling system pressurising) or water pump
 

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I'm doubting you are getting the system fully topped off since the heater should be working. A low coolant level would also cause overheating due to lack of circulation.
How is the level in the radiator after the engine fully cools off?
Are you sure the water pump pulley is turning since that could cause similar symptoms?
If any amount of steam is coming out of the radiator that would also indicate it isn't full.
To be sure everything has a chance to function properly reinstall the thermostat.
 

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As long as the thermostat has been removed, suggest that you buy a new one, and then install it as Dr. Dyno mentions. With the thermostat removed the coolant circulation is basically through the engine and radiator, while with the thermostat installed when it is in the closed or partially open position that helps to force coolant also through the heater core. Also as Dr. Dyno suggests the coolant pump pulley should be checked to make certain that it is turning, and from the description of the symptoms it could be that the amount of coolant in the system is not sufficient - there may be an air lock. Further, if using a cooling system sealant the coolant should be at normal operating temperature while adding it,, rather than cold. Adding sealant to cold coolant has been known to cause the sealant to ball up in the engine cooling system, creating blockages.
 
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