Missing coolant (aka, well crap...)

[slomatt]

I haven't driven the 4Runner for 2 weeks so this weekend I decided to give it a bit of exercise and figured I'd do a quick fluids check first. It turns out the radiator overflow tank is bone dry, and looking in the radiator cap I didn't see any fluid. Obviously this is not a great thing to see. The truck also been loosing some oil recently, which I think is due to a leaky valve cover gasket.

The oil on the dipstick looks normal and not milky, so I'm really hoping this is not something dumb like a blown head gasket (truck only has 110k miles), and instead suspect a coolant leak somewhere such as the rear heater lines. So, the plan is to remove the skid plates, put some water in, bring things up to temperature and look for leaks. As a precaution I'll also pull a couple spark plugs and look for any signs that coolant is getting into the combustion chambers. Any other suggestions on how to debug this?

- Matt

[Robinhood4x4]

Your year isn't really prone to head gasket problems so probably not that. I could be hoses, but I'd guess water pump. Check the weep hole, there might be crusty red stuff around it.

[4x4mike]

Our engines aren't know for HG problems but it's not unheard of and does happen. As far as leaking do you or do you recall smelling any coolant? Our Subaru had a pin hole leak on the top plastic of the stock radiator and I could smell it 10 feet away. It was small enough I wasn't too concerned but did watch it while a new radiator was ordered.

Two weeks is a while but a leaky heater core may wet carpet in the cabin so run the heater and check the carpet. In two weeks if it did leak I'm sure it's dry but maybe check for discoloration or smell in the carpet near the firewall/footwells.

Keep us updated.

[paddlenbike]

I haven't owned a Toyota truck yet that would keep any measureable amount of fluid in the overflow container.

[Seanz0rz]

I've had the IAC gasket go bad and burn up coolant that way. It was extremely slow, but it would empty out the overflow tank pretty often.

Ken, I had that problem for a while, but now my tank stays where I fill it to. Not sure what I did different, but it seems to be working.

I would look for some external leak in the cooling system, likely a pinhole in the radiator or hose (have the hoses ever been changed with such low mileage?) or heater core.

[4x4mike]

The overflow tank has always baffled me. It gets filled when the radiator gets hot enough and has enough pressure to push the cap up and have fluid pour into the bottle. To me if it's empty it's not a big deal. Right? Fluid can't get back to the radiator as the overflow is not pressurized and even if it were the radiator cap acts like a one way valve most of the time. I know some European cars are different but our Subaru and the 4Runner are as I described.

Matt, I think that if you had a leak you'd see or smell it as the truck has not been moved for 2 weeks. Even if it happened coming down the mountain I think you'd pull into your parking spot hot and pressurized.

Have you opened the system recently? Like Sean mentioned, the IAC has coolant lines to at albeit small and at the highest point of the system.

[Seanz0rz]

As far as I know, the "overflow" tank supplies coolant back into the system as it cools, and should always at least cover the bottom of the tube when cold. There are low and full marks on the bottle as well. Maybe I misunderstand that process, but that was always my assumption.

[4x4mike]

Not to totally hijack Matt's post but I thought it worked the same way Sean. Except when you think of it how can the bottle supply the radiator? I guess under some kind of vacuum the radiator could suck it back in but the radiator is a pressure vessel or sorts. The inlet to the over flow hose is also between the seal of the radiator cap and the bottom of the cap which is held in place by a spring. As the vessel gets hot, it pressurizes and pushes up the spring to allow overflow. To get it flowing the other way is a mystery to me.

Edit: Mystery solved?
http://auto.howstuffworks.com/cooling-system7.htm

I guess it does pull a vacuum. The "other" spring was something I didn't know about. I don't think I've even been able to keep an overflow bottle with coolant in the Toyota or Subaru. My Chevy truck could but that tank was well over a gallon.

[Seanz0rz]

Actually, inspect the hose system and bottle for cracks or leaks. It might be a non pressurized part leaking, especially since you haven't had an overheat. On my friend's '82 3/4ton, his overflow bottle disintegrated because after driving home every day, his dad, and then him, opened the hood to cool the engine off. What saved most of the underhood parts ruined the bottle, since it was not UV stable.

[garrett]

Not to totally hijack Matt's post but I thought it worked the same way Sean. Except when you think of it how can the bottle supply the radiator? I guess under some kind of vacuum the radiator could suck it back in but the radiator is a pressure vessel or sorts. The inlet to the over flow hose is also between the seal of the radiator cap and the bottom of the cap which is held in place by a spring. As the vessel gets hot, it pressurizes and pushes up the spring to allow overflow. To get it flowing the other way is a mystery to me.

Edit: Mystery solved?
http://auto.howstuffworks.com/cooling-system7.htm

I guess it does pull a vacuum. The "other" spring was something I didn't know about. I don't think I've even been able to keep an overflow bottle with coolant in the Toyota or Subaru. My Chevy truck could but that tank was well over a gallon.

i love how stuff works. i remember reading the article on how an IC engine works back when i got my 4runner (first car) and it was a big reason for me getting interested in maintenance/DIY/modding to begin with.

[Robinhood4x4]

Ken, I think in my entire life of owning toyota's the only time I've ever filled the bottle was when I had a known leak. Otherwise, there's always water in there...

Ok, that's a slight exaggeration, but not too far off. I hardly ever have to fill the bottle.

[paddlenbike]

Ken, I think in my entire life of owning toyota's the only time I've ever filled the bottle was when I had a known leak. Otherwise, there's always water in there...

Ok, that's a slight exaggeration, but not too far off. I hardly ever have to fill the bottle.

Mine is always nearly empty, with just enough fluid to cover the bottom of the tube. If I fill to max, on a 100+ degree day it will just dump all the extra coolant out of the overflow tube of the overflow bottle. So there's always some, but not much fluid.

[slomatt]

I crawled around under the truck this morning and didn't see any obvious signs of leaks around the rear heater hoses. I also checked the carpet near the rear heater it is dry. And there are no obvious signs of leaks in the engine compartment, but the water pump is difficult to see so that is not a 100% valid test. It is still possible the heater core behind the dash is leaking.

This afternoon I refilled the radiator with distilled water, it took about 1/2 gallon. Tomorrow I'll see if the level dropped overnight, and if not then I'll get the engine up to temperature and see if there are any leaks. When my WRX's radiator failed it had a pinhole leak that would spew coolant under pressure, and you could definitely smell it. Mike, to answer your question I have not noticed any coolant smell with the 4runner. Oh, and I haven't previously opened up the cooling system for quite a while, probably many months.

Does coolant flow through through the side of the IAC opposite where the air bypasses the throttle plate? I don't remember ever replacing the IAC gasket on the 4runner (done it many times on the WRX) so that is definitely a possibility.

The big hassle here is I have the Land Rover pretty disassembled so I need to get it at least rolling so I can move the 4runner into the garage to work on it.

- Matt

[4x4mike]

Half a gallon isn't too much, especially if you haven't really been monitoring the system. With your frequent trips up the hill with the heater going it's possible you sent some fluid into the overflow and it never got sucked back in only to disappear in the known mystery chamber that is the overflow bottle.

Our Subaru is a hot little motor and like you had the pinhole leak and stunk, especially when it sat in the garage warm. I'm thinking that whatever you have if anything is really small. I've had my IAC and TB off a couple of times as have others. Most of the time it requires some monkeying to get the coolant lines back on without a drip leak. If you haven't had yours off it's something to check anyways.

This is a random google image but it shows that is bolted to the TB. The IAC is controlled with the plastic piece. The barb like fittings are the coolant hoses.

http://i305.photobucket.com/albums/nn215/dunniganw/4Runner/IMG-20120122-00126.jpg

[Seanz0rz]

I had mine leak between the upper left chamber and the lower chamber (as shown in that picture). I used RTV to make a new gasket, but that didn't work all that well either. I eventually broke down and bought a new one from Toyota.

Again, I doubt that is your problem, it only really occurs if you remove it often and accidentally pinch the O ring. Or you didn't get the bolts tight.

I suspect it is just a case of not paying attention to it much and it getting lower than you thought it was. I've done that many, many times.

[slomatt]

I had mine leak between the upper left chamber and the lower chamber (as shown in that picture). I used RTV to make a new gasket, but that didn't work all that well either. I eventually broke down and bought a new one from Toyota.

Again, I doubt that is your problem, it only really occurs if you remove it often and accidentally pinch the O ring. Or you didn't get the bolts tight.

I suspect it is just a case of not paying attention to it much and it getting lower than you thought it was. I've done that many, many times.

The truck hasn't had any issues with idling so I haven't had the IAC off to clean it out and check the gasket, but I agree with you that it is unlikely. You and Mike are hopefully right that I just didn't notice the coolant level going down over time and it either evaporated slowly or magically disappeared in the overflow tank.

Thanks for the input.

- Matt

[4x4mike]

magically disappeared in the overflow tank.



Seems legit.

[slomatt]

Today I popped the hood and looked for any wet spots. The only thing I saw was a small damp area way down on top of the oil pan on the front driver's side of the engine, somewhat below where the bottom radiator hose goes into the engine. I brought the engine up to temp and this spot evaporated, so it must have been water and not oil. I guess it could be a slow drip from the coolant inlet or possible from the water pump.

I took the truck for a drive and everything was fine, no noticeable coolant loss by the time I got back. Cross your fingers it was just low after not looking at the coolant for a couple years.

- Matt

[Kryptoroxx]

Hey that's good news!! I don't like messing with coolant personally.

Sent from my SAMSUNG-SGH-I727 using Tapatalk

[DHC6twinotter]

Good news! Hopefully it won't leak anymore. When I removed the water pump on my 3rd gen, I noticed signs of a very small leak.

My overflow tank always has coolant in it.

[YotaFun]

Quick question, you said the truck has 110k on it, have you done a timing belt and water pump on it yet?

In my time at Toyota, doing timing belts, majority of the time during disassembly I would find the water pump leaking, usually 9 time out of 10.

On the 3.4l it is really hard to see because the fan pulley being right there.
When I first got the truck I always had a slow leak but didn't think anything of it cause it wasn't overheating or running well just as you described, when it finally came time to do the belt, during disassembly I found that my pump had definitely been the cause for the slow leak.

Keep and eye on it and see if it persist.

[CJM]

When I did my timing belt I ran into an interesting issue: The spring loaded hose clamps dont seal all to well if you put new hoses on and clean up everything. The t-belt had last been done about 120k ago and I guess the corrosion and whatnot had made it seal. once i did the job it leaked at the rad and the engine. Replaced the clamps with screw on clamps, no more leaks.

[4x4mike]

Avi and others, regarding the water pump. Does a factory water pump say Toyota or have a part number on it? I was deep in the front of my engine for some time today messing with the belt and the fan. I think that maybe my water pump has been replaced and I was wondering if I can tell if it was a factory part.

On my radiator support there is a sticker that says the timing belt was done at 59,xxx miles. Six years ago when I was looking to buy a 4Runner it was extremely common to pop the hood and find one of those stickers. I think the dealerships just had a roll of stickers and put it on there. Why else would the timing belt be done so early.

[Seanz0rz]

Service interval for "severe conditions" is 90k miles for the timing belt. Basically, towing, driving in hot conditions, offroad, etc, etc.

I have always considered it to be 60k, especially in hot and dry SoCal. I don't even see a listing of recommended time to replace timing belt for "normal" conditions.

Being a non-interference engine, the timing belt is not as critical as it is on an interference engine. That being said, it is not worth the hassle of being stranded for $300 in parts.

[DHC6twinotter]

IIRC, my water pump says Aisin on it, but not 100% sure. I'll have a look tomorrow when it's daylight.

[CJM]

IIRC, my water pump says Aisin on it, but not 100% sure. I'll have a look tomorrow when it's daylight.
I got mine from the ebay seller with the t-belt kits and mine says Aisin on it.

[slomatt]

Quick question, you said the truck has 110k on it, have you done a timing belt and water pump on it yet?

In my time at Toyota, doing timing belts, majority of the time during disassembly I would find the water pump leaking, usually 9 time out of 10.

On the 3.4l it is really hard to see because the fan pulley being right there.
When I first got the truck I always had a slow leak but didn't think anything of it cause it wasn't overheating or running well just as you described, when it finally came time to do the belt, during disassembly I found that my pump had definitely been the cause for the slow leak.

Keep and eye on it and see if it persist.

As far as I know the timing belt has never been done so it is definitely overdue and on the list of things to take care of, but I haven't had time yet. I might just break down and have a shop do it since my plate is full of house remodeling projects.

It does appear that something is leaking a small amount of coolant from the front driver's side of the engine down onto the top of the oil pan, which could possible be the water pump. That would make a lot of sense.

Anybody in the Bay Area know of a good shop where I could get the timing belt done? Preferably in the East Bay?

- Matt

[YotaFun]

I can't remember exactly what was on it.
I don't think a part number is but I believe Aisin is printed on it.

Also while you are at it, iirc there is a small rubber hose that connects to the side of the water pump, for you Cali guys with the dry heat you might want to get it replaced.

[slomatt]

I took the 4Runner on a ~250mi trip this weekend and it did fine, no apparent coolant loss. My guess is I have a very slow leak on the water pump so I'll keep an eye on the coolant level until I change out the timing belt and the water pump.

Later this year we're taking the truck on a week long trip around Oregon so I've got some other preventive maintenance to do for that trip. LBJs (already bought), O2 sensors, and engine/trans/diff fluids. I might also look into swapping out the clutch because I'd like to not have to deal with the heavy clutch issue for an entire week.

- Matt

[Robinhood4x4]

I used to go to autotron in Pleasanton. They offered to evacuate my R12 while I worked on my AC over the weekend, then they ended up adding some more for free.

[4x4mike]

I took the 4Runner on a ~250mi trip this weekend and it did fine, no apparent coolant loss. My guess is I have a very slow leak on the water pump so I'll keep an eye on the coolant level until I change out the timing belt and the water pump.

Later this year we're taking the truck on a week long trip around Oregon so I've got some other preventive maintenance to do for that trip. LBJs (already bought), O2 sensors, and engine/trans/diff fluids. I might also look into swapping out the clutch because I'd like to not have to deal with the heavy clutch issue for an entire week.

- Matt

Where are you heading in OR? We'll be in Shasta, Bend, Crater Lake area and all the dirt trails in between in late July and early August. On the way home we're heading through Crescent City/Smith River before cutting over to Redding.

[slomatt]

I used to go to autotron in Pleasanton. They offered to evacuate my R12 while I worked on my AC over the weekend, then they ended up adding some more for free.

Thanks Steve, I'll check them out.