Hey all,

I recently bought an '04 V6 Sport with 160k miles on it.

I've had it for almost a month at this point and it's doing great. EXCEPT, it's losing a significant amount of coolant and sometimes overheats a little bit (~213 degrees).

I haven't had an actual CEL or anything like that. I know it's overheating because my insurance OBD2 plug-in has 4 overheating codes on it. All are after the truck has been on/driving for well over an hour. The first one happened after going through quite a bit of mud (see my signature pic), and it's happened 3 times since on a long trip (3 day trip, driving 2+ hours each day)

I first noticed the coolant loss after getting home from said trip. I checked my oil/coolant at a gas station and noticed that the coolant overflow reservoir was nearly dry (just a little bit left in the bottom). It was full when I bought the truck. I'd put ~1,100 miles on it at that point, 500 of which were in the 3 days prior.

So, I ran by my local dealership, got some SLLC coolant and topped off the reservoir.

I drove the truck home from work (~10 miles), but don't think I checked the coolant there. I then drove it to work this morning, checked the coolant and noticed that it was at almost the same level in the reservoir as it was after the 500 mile trip.

There are signs of a decent amount of coolant spraying out of somewhere. Possibly my overflow cap? There are signs of it even on my intake piping and a decent number of drips below the overflow bottle. I've ordered a new higher-pressure radiator cap in case that's not letting the system pressurize properly and the coolant's boiling.

There are DEFINITELY air bubbles in my coolant, as I hear the water rushing sound through my heater core on cold starts.

Recommendations for what to check next? I'm thinking I'll burp the cooling system and check all hoses/radiator for leaks (though a quick check didn't find any) once the new cap comes in, but I'm not sure what to check if that doesn't help.

I'm obviously afraid of a headgasket failure, but it's not showing signs of that other than the loss of coolant. Power is fine, no CEL, no white smoke other than the usual cold morning condensation.

Sorry for the novel! Thanks for any help you can give!

I would try to figure out where that coolant is coming from ASAP. It's possible it could be from a bad radiator cap and those are cheap enough to buy one and try it. I would also examine the radiator itself as 12 years in service is about when some start leaking. The next place to look is the water pump. Overheating seems to be a precursor to headgasket failure on these earlier V6 motors.

Yeah, I fortunately have 2 cars, so I don't have to drive the 4 Runner all the time....but my unreliable 3000GT is the reason I bought the 4 Runner. HAH

I'll give the 4 Runner a good look-over tonight/this weekend. It almost seems like the coolant only goes down to a certain level and then stays there. What could cause something like that?

I'm also wondering if offroading clogged mud between my radiator/AC condenser. I cleaned everything out, but I can't really see how well I washed those out. I'll spray water in there tonight and see what comes from between em. That wouldn't really explain coolant loss though, unless it got punctured at some point.

Will the water pump show signs of coolant around it? Leaking from the gasket maybe? I've heard of it instantly evaporating and not showing any residue.

Yeah, that's why I'm worried. I'm afraid of it overheating and warping something. Which will definitely cause a HG failure if that isn't already the issue.

If it IS the HG it needs to show its face soon, cuz I have 2 months left on a warranty from the dealer that specifically covers headgaskets.

If you have a warranty I would take it to them and have them check for the problem. Especially since the head gasket might could be an issue.


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It's one of those 3rd party extended warranties where I have to call them and take it to their shop that'll probably charge me $200/hr. I believe I'm responsible for $100 of the cost or something like that. Which I'd prefer not to spend if it can be avoided. And if it isn't the HG and they do 4 hours of diagnosis, I'd rather not get bitten by that. I've done a lot of work on my other car, but have somehow never had to do anything relating to cooling system problems. Which is why I'm asking for advice.

I'm going to get a Blackstone Labs analysis done to check for coolant in my oil, though it looks very clean (~1k miles since the last change), and the coolant is perfectly pink (no signs of oil in it).

Also going to pressure test the radiator/radiator cap soon (hopefully this weekend).

As of right now, I've determined that it's probably not the headgasket, as I'm sure I'd notice half a gallon of coolant being burnt out my exhaust and that a rough idle/misfires/CELs would accompany it.

However, if it keeps overheating, things could warp. So I'll work on finding the problem ASAP

Replaced the radiator cap with an 18 PSI TRD one, inspected/changed the spark plugs and other than an excess of antiseize on some they look fine, burped the cooling system and got a good amount of bubbles. I'll probably burp it again tonight to get anything I might've missed.

Look for pink crust below the water pump area and the top of the front crossmember.
Water pumps are a known issue.

Can pull the plugs and compare color, these motors seem to burn the headgasket out mostly on cylinder #6.
Most likely no oil in radiator because of the way these fail.
http://www.toyota-4runner.org/4th-ge...%2A%2A%2A.html

Still no recall.

I thought I saw some coolant around the WP, but it looks like it's just drippage from the overflow hitting the fan. At this point it looks like the cap was just faulty. Definitely needs to be burped again though, cuz it made the water rushing sound again when I turned it on to go to lunch today.

I replaced the plugs since I didn't have a clue when they were done last. They looked fine other than some oil around the coil packs. Guess my plug o-rings in the valve cover gasket are getting old.

I would seriously look at the water pump. I just bought mine and just took it back today because the dealer had the water pump (and timing belt) replaced because they found a leak when they got it on their lot. I took it to a Toyota dealership for a prepurchase inspection and said it was still leaking. The dealer is going to have their mechanic fix it again in the morning. My coolant bottle had been drained as well but fortunately there was no over heating. To be fair though I have only driven it about 70 miles.

Unless your belts and engine are also coated with coolant I would highly doubt just the water pump would show signs of coolant on it if it weren't the source.

There was coolant sprayed up on my intake piping and the passenger hood strut. The water pump isn't out of the question. I took a look and couldn't see any leakage around it while I was burping the coolant.

Opened my radiator cap today after the car sat 8 hours at work. Cold coolant sprayed out onto my hand. AKA I most likely have a bad HG.

Gonna get the system pressure checked and compression tested. I have a month/1200 miles left on that warranty and want to get this replaced before it'll come out of my wallet

As best I can tell, the pressure in the system (from cylinder compression coming through the leak) is pushing the coolant out until the reservoir is topped off. At which point it pushes it out of the overflow tube. The system then never depressurizes, so the coolant never goes back into it. Eventually it'll just fully drain my cooling system of all coolant. It doesn't seem like there's any getting into the oil though or being burned, so it must only leak under high pressure and doesn't have enough pressure to leak back into the cylinder.

Well, I was (fortunately) wrong.

Took it to a friend's shop earlier this week and it passed the hydrocarbon test 3 times after extensive driving/idling each time. So it's not the headgasket! It is, however, leaking coolant somewhere (failed the pressure test). So he dyed the coolant and couldn't find anywhere that it leaked out.

Ideas? Very small heater core leak maybe (which is why he couldn't see the leaked dye)?

FIXED

Replaced my radiator last week, and after driving 11+ hours this weekend in different intervals (up to 5 hours at once) and having no residual pressure in the system after letting it sit for several hours after each time, I'm considering the issue fixed! The coolant is also now actually dropping to the proper level once it cools down.

The old radiator had a small leak above the petcock and was *covered* in mud on the back, which I'm sure didn't help the fan's job trying to cool it. I'm also fairly certain it was clogged, as when I drained it, only a gallon or so of coolant drained out. But after removing it, flipping it around several times, more coolant proceeded to unexpectedly pour out.

I'm still getting the water rushing sound when I turn the truck on sometimes, but I'm assuming I just need to burp the coolant more, as the front wasn't elevated when I burped it last time. So, the heater core was definitely above the radiator cap.

So, hopefully anyone that finds this and has similar symptoms as myself will be able to come out of it without a headgasket replacement...