Coolant level dropping

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The coolant level is dropping on my Rav4. About 12-16oz per 500 miles. I don't see any external leaks, no smell of antifreeze when I turn on the heat, no white smoke out the tailpipe, no chocolate milkshake on the oil dipstick or under the oil cap. A friend mentioned the intake gasket but the intake manifold is plastic so I don't think it's part of the cooling system. Just put a new radiator cap on it but I don't think that was the problem. I hear the sound of water flowing for about a second or two after first starting the engine. No problems with overheating....yet.

Any ideas where to look or how to troubleshoot this?
 
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If you can try to visualize the water pump, look for traces of white or red residue below the weep hole on the bottom side. It may only be leaking when hot and thus not dripping enough to leave a mark (on your driveway). Check all your system hoses for the same signs.

12ozs/500 miles is quite a bit, though. Has it done this numerous times, or you just noticed it once in that span?

Have you checked the overflow tank lines and that they are secured with clamps? I was recently losing a little bit or coolant in a car, and it was from these lines losing a small amount with each expansion. There should be two hoses in the tank cap, one coming in from the radiator cap overflow, another exiting and going downward as a vent. If the second one is missing, it will increase evaporation as a source of loss, also.

The gurgling sound is probably air in the system trapped at a high point in the heater; it probably got sucked into the system via the overflow tank when it was low. Once you figure out the source of the loss and repair it, you can then purge the system and that will go away.
 
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I noticed the overflow reservoir was empty about 3 weeks ago. Filled it to the "cold" line. Notice it was empty again a week later and filled from the radiator cap. So, it's been about a quart in the past 2 weeks. It driven about 500 miles per week.
 
The radiator can leak when hot but evaporate the coolant so hard to detect. Weep hole for water pump.

The have adapters to pressurize the cooling system when cold. UV dye and UV light.
 
When was the water pump last changed? Is it easy or part of timing belt?

If normal fan belt driven and you have not replaced it in last 100k miles, maybe replace it as PM.
 
If it's the 4 banger 2AZFE, those are the ones that have head gasket/stripped headbolt issues. The headbolts strip in the block and the head comes loose and leaks antifreeze externally under the intake manifold at the back of the engine; you usually don't see the leak because there is some kind if diaper thingy to protect the engine and it soaks up the antifreeze.

http://www.rav4world.com/forums/88-4-2-f...eliability.html

VERY GOOD video detailing the issue and the correct fix:
 
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If the water pump was leaking that much, it would be dripping on the ground and the front of the engine would be covered with antifreeze.
 
It's still the original water pump. It's not too bad of a job to replace it. It's just part of the drive belt. It's a timing chain engine.
 
Originally Posted By: Drew99GT
Which engine do you have???


It's the 4cyl 2AZ-FE15. Looks just like the one if the video above.
 
Originally Posted By: Drew99GT
If it's the 4 banger 2AZFE, those are the ones that have head gasket/stripped headbolt issues.



Ugh. I forgot THAT engine and issue was in this y/m/m. That much coolant, that fast - if you can't see easy evidence at the WP or somewhere, this has to be suspect #1.
 
Originally Posted By: Oro_O
Originally Posted By: Drew99GT
If it's the 4 banger 2AZFE, those are the ones that have head gasket/stripped headbolt issues.



Ugh. I forgot THAT engine and issue was in this y/m/m. That much coolant, that fast - if you can't see easy evidence at the WP or somewhere, this has to be suspect #1.


What's suspect #1?

I pulled the wheel and wheel cover so I could see the water pump. Nothing looks water wet under there. Some oil leak on the water pump but no water. Everything under the car is dry after running it for 30 minutes and then taking if for a drive. If it's a head gasket, we're getting a new car.
 
By "suspect #1" I mean if you can't see an obvious leak, the 2az headbolt issue is the #1 thing to check out.

It's not terribly easy to fix, but it can be done. Check out the link Drew provided above to the repair kit. You take the head off, tap improved bolt holes in the block, then install an improved head gasket and bolts.
 
Originally Posted By: Olas
+1 on the water pump but pressure test it when cold to confirm.


Yes, water pumps can intermittemtly leak at odd times which I believe is his leak source.. An oil analysis would be on my list. It takes a lot of coolant to make the oil look like a milkshake. If coolant is used to warm the throttle body, it could have a passage in your plastic intake manifold as my GM did and the oil looked good. An analysis detected coolant in my oil.
 
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I picked up a pressure test kit from AutoZone. Will test it soon.
 
Not that it's related but doesn't this car make a ton of noise while driving? Like a bad wheel bearing or something.
 
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