wohv

Hello, I purchased my 2005 GX470 in Feb with 124,000 miles. It's at 128,000 now and I noticed the coolant reservoir was empty so I filled it back up. It emptied back out with fluid sprayed around the reservoir and a leak from the overflow tube. I got a new radiator cap and topped of both the radiator and reservoir and it's still leaking from the reservoir cap overflow tube. What do you guys think the problem could be? I've driven the GX 300 miles round trip with no overheating before I noticed this so I'm hoping it isn't something major. Also, there is no white smoke from my exhaust so I'm ruling out a headgasket failure.

IanB2

Have a look under your oil cap, is there any buildup? If yes, post a pic. Headgaskets can fail in many ways, I don't think you can rule it out just because you aren't seeing white smoke from the exhaust. The coolant system is pressurizing to be pushing coolant out like you've described.

LoneHiker

What IanB2 said is correct. Look at the inside of the oil filler cap for a milky colored film. If you see that, you have a head gasket leak, regardless of whether it smokes or not.

It's also possible your new radiator cap is the wrong one (wrong pressure settings) or bad out of the box, so don't panic yet. It could also be crud in the seat for the radiator cap or warpage or cracking around that area. A radiator cap has to be able to let fluid out at the correct pressure of course, but it also needs to draw it back in at the correct time. If it's failing to draw it back in correctly it can easily cause these symptoms.

wohv

I checked the oil cap and dipstick, I can't find any milky buildup. There was some buildup under the oil cap but it looked more like dirt, the dipstick is totally clean.

neub

Assuming, I repeat assuming it is the head gasket - OP wouldn't see any of the following such as oil in coolant or coolant in oil. This sounds like an external leak. Check for dried coolant around the heads and and exhaust. Likely, The exhaust gas in the combustion chamber is being pumped into the glycol supply....but, given the unlikely HG event in the 2UZ, you may have air in your system. Get a spill free funnel and burp it. Is the radiator original? If so, it is 100% leaking in multiple locations, remove the fan shroud, get a flashlight and take a look around.

wohv

I did remove the shroud and checked for leaks around the radiator with a flashlight, it's very clean and relatively undamaged (minor scratches here and there). There are no leaks that I can find anywhere besides the reservoir cap where it's visibly leaking out once the engines warms up. Oh, and I did burp the system as best as I could when I did the top-off.

When I bought the GX, I had the dealer replace the secondary air pump under warranty since it had the dash warning lights and startup noises. Do you think they may have touched something or did something wrong during that replacement?

IanB2

So if I understand correctly, it's pushing coolant out the reservoir cap when the engine is hot, then sucking the reservoir dry as it cools off?

Is your new rad cap an OEM Toyota/Lexus? Almost sounds like it's not letting pressure vent, and is pushing fluid out the reservoir as a result. You mentioned something about a leak from the overflow tube? Can you explain that a bit more?

wohv

Yes, once the engine's warm, coolant begins to leak from the disconnected port (I called this the overflow tube earlier) on the coolant reservoir cap. Once the engine's turned off, the leaking stops. The new rad cap is not OEM, I picked it up from autozone.

I asked the shop that did the air pump replacement if the disconnected port is supposed to be connected to anything, however, they said it doesn't. The coolant basically drips at a fairly even flow from this port.

neub

You should have a rubber hose running from the radiator neck to the overflow / expansion tank. If you start the engine and the fluid starts pouring out of the overflow tank, the radiator cap seems to be not holding pressure. Stock cap should hold about 15psi, don't know what your aftermarket is rated for. Alternatively, if you're blowing out coolant from the expansion tank cap, and you have confirmed your radiator is fine, and your cap is holding pressure, and you burped the truck properly.... then it is news you do not want to hear.

wohv

There is a small rubber hose that connects to one of the ports on the reservoir cap while the other is disconnected.

The radiator cap I purchased is rated up to 16 PSI and shows no signs of leaks around it. Now I may not have burped the truck 100% since this is my first time trying to resolve an issue like this. I might just have to get the system pressure tested and hopefully it's nothing related to the head gasket.

IanB2

With the system filled, burped, and the overflow filled to the proper level, when you run the engine and it gets hot, it will push some fluid into the overflow and the level will rise a bit (but not overflow), then when it cools down it should suck the fluid back into the rad and the level in the overflow should go back down to the proper level.

This doesn't sound like it's happening to you. I'd start with an OEM rad cap, and see if it smartens up.

burny

I think it the cap too

neub

What's the update?

wohv

Sorry guys, I've been busy the past few days. I did a more thorough burping of the system and still no luck. I went out and purchased an OEM radiator cap and installed it late last night after everything cooled off. I will check on everything later tonight when I get back from work to see if the issue has been resolved.

neub

Doubt your new cap would solve anything. I'd go ahead with a new radiator, thermostat and hoses. DEnso is a good radiator, so is koyo. I forget the oem cap manufacturer. Google it.
Then refill new coolant. Then burp it properly. The burp is critical and you will not get air out until thermostat opens. If DIY ain't your thing - take it to a shop for a proper diagnosis.
Your Alternative is having it overheat and paying that same shop 20 labor hours to remove and resurface those heads because that will happen when you run out of coolant.

Good luck