Hey guys,

Here's the story. The 2000 LX470 belongs to my sister, so I wasn't driving when this happened, but here's what happened. After getting off the expressway she pulls into a parking lot and realizes her car is steaming and something is leaking from underneath the front of the front right tire. Calls me and the first thing I ask is to check the engine temp. It was in the red. So she has the car towed back to her house and yesterday I finally get a chance to crawl underneath it to see what's going on. As I crawl under the front I notice right away the remnants of leaking coolant around the right section of the radiator (without taking off the metal under cover). My first thought was that either the radiator sprang a leak or a hose came lose letting all the coolant drain and causing the engine overheat. I take off the metal cover and see the lower portion of the radiator still wet from the coolant (particularly the area around the drain plug). Inspecting the hoses, I didn't see any problems. No cracks in the rubber or the radiator.

So I decide to fill the system up with some tap water and see where the leak is since it's not that noticeable (the radiator looked pretty dry looking into the radiator cap). Fill it up, no leaks. Fire up the car, still no leaks. Engine warms up and the temp stays in the middle, still no leak. Hmm, tracking this down is starting to prove more difficult. Keep in mind that this whole time while the engine is running I am checking for leaks from the top and bottom of the radiator. I actually disengaged the fan shroud so I could keep a little closer at the radiator to see if any leaks are forming. So I rev the engine a little bit to get the terms up and let the water start moving. Finally the temp begins to creep up and I shut the engine down the away. But still no leaks.

So now I am at the point where running the car with regular water I got no leaks at all but it did begin to overheat. The couple of things that come to mind is that maybe the system was low on coolant, causing the engine to overheat and boil the remaining leftovers (she said there was a decent amount of coolant that came out though). Or could the thermostat gotten stuck preventing the coolant from circulating and overheating? From the looks of it, it doesn't look like the overheating was caused by a leak. Instead, it looks to be the other way around, the leak was caused by overheating. So does anyone have any suggestions on what to do aside from maybe replace the thermostat, flush the system with a hose under some pressure, and refill with some fresh coolant.

Thanks

-Yuri

 

How many miles are on it? Has the thermostat ever been replaced? Is the electric fan kicking in when the temp gets high? My first guess would be the thermostat. If the radiator had a crack or leak you would see it right away and see where the coolant is spraying out from.

 

The car has about 130k miles and I don't remember ever hearing about a thermostat change from my sister. And sorry for the stupid question, but where is the second fan located. I thought I only saw the one main fan yesterday. Unfortunately I won't see the car for a few days so I can't just run out to the garage to look for it.

Thanks

 

The most common, yet most often overlooked, cause of overheating is the radiator cap. If it does not hold pressure, coolant / water will boil well before it should and cause an overheat, which will cause a boil over... Boiling point is directly related to pressure in a closed system like this.

Definitely ensure that the cooling fans are working properly.

Also, when you added water, did you ensure that you got all of the air out of the system. Certain vehicles can be difficult to get all of the air out of the system and will constantly have overheating issues if all of the air is not evacuated.

 

If you don't see any leaks chances are that the thermostat needs to be replaced. If you take it in anywhere they are going to replace the thermo and gasket before they do any other checks because it is so common for over heating issues to be related to stuck thermo.

 

Actually, that is the least common reason for overheating... #1 is leaks, #2 is radiator cap, #3 improper fan operation, then we get to stuck thermostat at #4... #5 and worst of all of the above is headgasket / cracked head...

 

I agree with all of the above. Start with the simple/cheapest first. Sounds like the T-stat got stuck, causing the overheat, which caused the coolant to spray out of the overflow/radiator cap.

 

I would pressure test the system. I had a hard-to-find leak in my Toyota pickup years ago. I'd see signs of coolant blown all over by the fan, coolant level would be lower, but I never saw a leak until after driving it a couple of miles on a cold engine. Turns out the leak was around where a hose exits the block.

What happens is when the engine is cold, the radiator cap valve is closed, so pressure builds up in the cooling system until the valve in the cap releases pressure and allows the expansion coolant to enter the bottle. Likewise, when the engine cools down, the vacuum sucks the coolant from the bottle back in. A pressure test would reveal what is leaking (hose connection, radiator cap, etc.). If you just start replacing parts, you are just guessing. Before you pressure test, I'd park the car on an incline w/ radiator cap off and top off the system with coolant/water. Then run the engine until it sucks in the coolant from the radiator to ensure there are no bubbles in the block.

 

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