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Hello

I have a 1999 TOYOTA RAV4 (4x4) 4D WAGON 2.0L INLINE 4 4 SP AUTOMATIC 4x4.

The old girl over heats sometimes. It has a radiator we replaced around 24 months ago.

It will sit on 1/2 way up the factory heat gauge.

Then sometimes it'll go crazy up to overheating. But when you give it some throttle it'll come back down.

  • Heater works perfect.
  • A/C works perfect.
  • No smoke out of exhaust.
It may be losing some water. But the engine drives like it always did so I'm guessing not a cracked head or gasket.

I have burped all the air out of the cooling system.

Unsure what to do.
 

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Your Humble Administrator
2008 RAV4 Limited V6
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A general rule of thumb is if it overheats in town, it's the fan(s). If it overheats on the highway, it's the water pump. You could have a bad/leaky water pump. Or it could be the thermostat. Are the fans running properly? They should be on any time the A/C is on.
 

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It isn't good to let an engine overheat. You could have a head gasket issue even though you don't see any smoke.
If you are looking for a mechanic in a can, I recommend Bar's Leaks.


One test we do at the shop to verify a head gasket that is leaking coolant into the combustion chamber is to get the engine up to operating temperature and carefully remove the radiator cap. Fill the radiator to the top. Making sure the path in front of the vehicle is clear and have someone stand to the side to observe the radiator neck, put your foot firmly on the brake pedal, engage the parking brake and put the RAV in drive. Now press the gas pedal all the way down, and don't let the RAV move. Have the observer look for a geyser coming from the radiator neck. It is normal to see a little overflow, but if it looks like Old Faithful's little brother, then you have combustion gasses leaking into the cooling system. By brake torqueing like this, combustion pressures are increased.


Another test is to remove the spark plugs, disconnect the fuel injectors and pressure check the cooling system overnight. Have someone crank the engine while someone else observes the spark plug holes in the cylinder head for coolant escaping. Be careful - I saw a mechanic do this and the coolant blew his eyeglasses off! I always stick my fingers in the holes (more difficult on a V6) after verifying a large amount of coolant is not in the cylinders. Coolant will have a sweet taste.


If you can get each piston at TDC, look at the top of the pistons. You are not wanting to find one that is cleaner than the others. Coolant is a great detergent and eats carbon so if you have coolant in the combustion chamber, the carbon will be noticeably less on one piston more than the others.


If you are just trying to limp this along for a while, then Bar's Leaks is what I would use. Nothing else. I've been a mechanic for over 40 years, and I have a short list of chemicals that I know work :


Bar's Leaks - coolant leaks
PB Blaster - penetrating oil
Seafoam - fuel system treatment
 
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