Coolant Loss Question

[Blindaviator]

I have been trying to solve an issue with my 2001 Pathfinder for a few weeks now.

I have seen a lot of posts about overheating, leaky head gaskets, cracked block / heads, Etc. but nothing really helps me in anything I have found...

Short summary of my issue:
I picked up my 2001 about 2 months ago in california, the sacremento area, and drove it back up to the north end of cali (about a 7 hour drive) without any issues.
For about the next month I drove it locally without any issues. Then a few weeks back I decided to head back to Texas.
On the drive back I noticed I started losing coolant with no obvious signs of leaks. I first thought a head gasket but none of the other signs were present. The temp of the engine stayed steady and never showed any signs of being hot. Long story short I stopped occasionally and topped off the coolant (always used 50/50 mix) and made it to texas without further incidents. It ended up using exactly 1 gallon of coolant in the 2100 mile trip.

Once here I started having some small amount of coolant being pushed out into the reservoir so I replaced the radiator and main thermostat. That stopped the overflow but I was still losing some coolant. I replaced the cap and that didn't change things. I rented the chemical test for unburnt hydrocarbons in the coolant and it came back negative. I did notice after a good highway run I could hear air being pushed out from the cap. So I am assuming the coolant is being boiled off inside and the gasses pushed out of the system and that is why I don't see any coolant loss.

About an hour ago I decided to try bleeding the system again to insure all the air is out. From what I understand you are supposed to elevate the front of the vehicle (which I did) to help with trapped air. Then remove the radiator cap and the bleeder cap at the back of engine, start it up and add coolant until it starts to come out the bleeder hose. Cap the hose and radiator and drive it. Rinse and repeat until all air removed.

I removed the radiator cap and started the engine. The coolant inside stayed steady and seemed to be flowing. At that point I removed the bleeder cap and the moment it was removed the coolant in the radiator shot out like a fountain. I prolly lost 1/4 of a gallon in a second and it stopped the instant I put the bleeder cap back on. If you try starting it with both caps off the same thing happens.

I have never seen something like this happen before.
I am assuming this means there is a blockage in the system somewhere?
Would the water control valve cause this if it's stuck closed?
What else should I look at?

I'm hoping someone here has had a similar issue and / or more exp with these trucks to tell me what to look for...

[nickelghandi]

Was it already warm when you removed the bleeder cap? If so, then coolant would shoot out no matter what even if the radiator cap was already off. The coolant will displace most of the air when the system is pressurized. Some of the air can even dissolve into the coolant. That is why typically people remove the rad cap and bleeder cap before starting the engine. As the engine warms up, it pushes the air out. If the engine is fully warm, then the pressure is so great that it will shoot out the bleeder hole and even the radiator cap sometimes. I have bled the air out of my system on my 04 Pathfinder after replacing the thermostat and I used the same procedure, but I removed the cap and bleeder cap before starting the engine. I also ran a piece of aquarium hose from the bleeder cap down to a clean milk jug with fresh water in it beside the car so when the coolant came out it ran into the jug rather than into my engine bay and the driveway. The water let me watch it bubble the air out which it did for a while before coolant finally came out.

You haven't overheated yet which is good news. The bad news is, you are probably looking at a failing head gasket. I recently had this same issue with my Volvo. Coolant was disappearing and there was no reason for it. I ignored it and eventually the car developed a slight miss at cold starts. I used one of the hydrocarbon tests and it passed. I checked compression on all 5 cylinders (yes 5) and it was within spec, but one was lower than the rest. Finally, a little oil showed up in the coolant after I drove it pretty hard during an emergency. I put dye in the coolant, ran the car til warm, then let it cool. I pulled the spark plugs and shone a UV light into the cylinders. I found coolant in, you guessed it, the cylinder that had lower compression. That explained my misfire and confirmed my head gasket leak. I was still within specifications for cylinder compression on that vehicle, but had a head gasket leak. The Volvo is currently in the shop being torn down for the head gasket.

Those exhaust gas in coolant leak test kits really only work if there is a large leak pushing a large volume of CO2 into the cooling system. They are used more to confirm that the leak is pushing gas into the coolant rather than to decide whether or not there is a leak at all. A compression test is a better bet, but like with my Volvo, not always 100%. A leak down test is probably the best test and worth the $40 or so for it to decide once and for all. If you have any mixing of fluids at all then do not drive the car.

You can have it checked by a shop or dye the coolant yourself. Check all places that it could leak as well to rule that out. You can even borrow leak down test kits that you can use to pressurize your cooling system with it cold (and I mean overnight cold) and a gauge will read the pressure and measure any leakage. I hope it is not using the coolant internally, but there is a good chance since there is no sign of obvious leakage and you are losing a full gallon in 2100 miles.

Have you noticed any smell of coolant after driving? If so then that is a good indication of an external leak. Don't inhale it directly, but fan some of the exhaust into your face and check for a sweet smell on a cold start. That is a good indication that it is using coolant internally.

Edit:
Also welcome to NICO! Not many of us still here with R50 Pathfinder and Qx4's, but hopefully we can help you out!

[Blindaviator]

Thx for the welcome...

I looked for any bubbling or foaming of the coolant and don't see any... Checked for white smoke or sweet smell in exhaust and don't smell any... No misses on cylinders... None of the usual signs of head gasket or cracks are present other than the coolant loss...

When I pulled the bleeder cap off last night the engine was running and beginning to warm up... The radiator cap was off at the same time... I tried putting the radiator cap back on and removing just the bleeder cap and it didn't push any coolant out of the bleeder tube... I know the bleeder tube is open as I have used a vacuum pump to pull coolant through it in an attempt to remove some air...
A few days ago I tried starting it with both of the caps off and it still shot the coolant out (overnight cold engine)... I will head outside here in a few minutes and try again to see if it still occurs...

By leak down test you mean pressurizing the coolant system and watch for it to leak back down?

[Blindaviator]

Ok so I just now went out and removed the radiator cap and bleeder cap (overnight cold engine)...

The second it started it shot coolant out of the radiator at an astonishing rate... It was started for just a split second and it likely lost close to 1/2 of a gallon... It covered the hood, windshield and top of the engine completely with coolant... If I put the bleeder cap back on it will not do that...

The only way it could have done that is if the coolant was coming directly from the water pump... There has got to be some blockage in the system somewhere causing it to do that...

[nickelghandi]

On the leak down test, yes. You are on the money. The coolant has to be going somewhere and the leak down test will confirm that it is indeed losing that pressure.

Sounds like you are doing all the right things to check so far.

I would dye the coolant and and then check EVERYWHERE for signs of leakage internal and external. The dye will show with UV Blacklight very brightly. You can check all of the usual places for external leaks and check the oil and transmission fluid as well. Oil and ATF always glow a tiny bit under UV light so don't panic if it does glow a bit. If there is coolant in there, it will glow brightly.

If you don't find anything in any of the fluids or evidence of any external leaks then I would pressurize the cooling system and if it loses pressure, check the cylinders. A tiny leak may not cause a misfire at first. It is entirely possible that it is leaking externally, only while running or even just under load as in accelerating or holding speed. In that case the coolant would pretty much be vanishing without a trace. The dye should still catch it under UV light as trace amounts would be left wherever the leak was occurring and the light would make it glow.

I don't think that your system blowing coolant through the bleeder valve is out of the ordinary. You might just have it too full or a large air pocket that causes violent bubbling when the pump starts or the system is pressurized. You can keep the radiator cap on during the bleed procedure. It will not hurt anything. The bleeder valve is supposedly the highest point in the system so any air should find its way out no matter what.

I would dye the coolant and look for leaks. Regardless of where the leak is, that should find it. It is cheap and easy and will almost certainly give you a definite answer.
1: Put the dye in the radiator; not the overflow reservoir.
2. Run it with the dye in it to circulate it around. Maybe even drive it around a bit to let the coolant push its way throughout wherever it is getting out. Then let the vehicle cool down.
3. Check all external coolant lines and places where coolant could be leaking.
4. Check all fluids for signs of the dyed coolant.
5. Check all 6 cylinders for signs of the dyed coolant. I would do this last on a Pathfinder because the plugs are a PITA to get to.

If you cannot find the coolant leak anywhere with that, then I am out of ideas lol.

[nickelghandi]

Yeah that sounds like a blockage. Is your radiator in good shape? Any major dents or holes even? If it is badly damaged from a rock then that could both cause a blockage resulting in that high pressure and a leak from the radiator where the damage occurred that only presents itself when the pressure is way up.

Also your thermostat could be stuck closed.

[Blindaviator]

Hehe the water is not coming out of the bleeder tube it is coming out like a geyser from the radiator filler neck but ONLY when I remove the bleeder cap... I cannot see back there and I can't find any good images of where that bleeder tube originates... Is it attached to the top of the water control valve it's self or off to the side some?

I replaced the radiator and front thermostat 3-4 days ago thinking those could be the issues...

I have finally had enough and decided to pull it apart down to the water control valve and see what's going on... While I have it apart I am going to be detaching every coolant line I can find, and reach, and using a water hose to blow water through it... Want to make sure none of the hoses are clogged... Will try to take a good look into the block as best as I can to see if there are any issues in there...

Will replace the thermostat while I am in there as well as the hose and the gasket for where it attaches to the block just in case... Don't wanna get it solved and then find I have a leak from one of the components I disturbed while doing the repair and have to tear it down again...

[Blindaviator]

Think I might have found my problem... What ya think??
This is how it looked after cleaning it off some... It was way worse just after removing the housing but I didn't think to get a picture then...

Taking a water hose to every hose I can get loose and cleaning out the system... Just as an FYI you prolly shouldn't use Bars-Leaks Liquid Copper on these engines... It is good for a regular cast iron system but these with 2 thermostats obviously don't like it...

[nickelghandi]

That definitely looks like a problem. It is probably THE problem causing the massive pressure build up and possibly even a leak somewhere. With that replaced you may not have the issue anymore, or there could be other places that the Bars-Leaks has gotten into. The VQ3500 motors have a ton of tiny little coolant passages that could also be blocked by that junk. You might be looking at some other issues down the road involving your cooling system.

In general, I stay away from that stuff. I am surprised you weren't blowing coolant out from the overflow tank. Did you put that stuff in there or did the previous owner? If they did it then you may still have a head gasket leak that they just didn't tell you about.

[Blindaviator]

Unfortunately I put it in there when I first started having my coolant loss issues on my trip... I had no issues with overheating or coolant loss before the trip...

I started taking loose just about every cooling hose I can reach and used the water hose to blow them out... Blew through the heater core both directions and use the hose end to push clean water into the block and let it run clear from the water outlet inside the valley to make sure I got everything possible out of it... Used a small hand pump to remove excess water from the block and the valley floor...

I might pick up some chemical flush and run that through after getting it back together to remove as much of the stop leak as possible and clear any small blockages that may be present... Don't really like using the stuff especially on higher mileage motors as it will sometimes cause a weak seal to fail... Will prolly only use it if I have any more blockage type issues...

[nickelghandi]

Well at least you know how it got in there and no one was hiding anything from you.

When you refill the cooling system, put some dye in along with the new coolant/water. Then just drive around normally for a while. Check with a UV light for leaks after that using the procedure I described above and you will probably find the leak. If you don't find any leak and have stopped losing coolant, then you may have solved your problem with the Bars-Leaks fix. In that case, the dye can be left in the cooling system and if you ever have a leak again, it will make it easier to find.

[rgk]

OK, you put it in there, but...

that still doesn't explain why you lost a gallon of coolant in 2100 miles, nowhere to be found.

I was losing a bit of coolant at one point, and it turned out that I had a crack at the top of the radiator. The system never got full because every time I filled it up, it would trickle out. But I didn't see signs of it, because it was trickling down only when I drove at high(er) speeds (and thus, pressure). It would then 'stop' leaking as the coolant level dropped, because the coolant was no longer reaching the top of the radiator.

Finally, the crack became big enough so that I could smell it after a highway drive. It heated up, expanded, and squirted all over the engine.

[rgk]

Also, a common problem on these cars is the failure of the idle air control valve. The IACV has coolant running through it, and the rubber gasket on the IACV fails after about 10-15 years. When this happens, coolant infiltrates the intake and fries the IACV, then the ECU. It could be something to check.

Do you know how to pull the plenum on this car? How about the IACV? Maybe just remove the rubber hose and open up the throttle body, and shine a flashlight inside? Are you having any idling issues?

[Blindaviator]

Also, a common problem on these cars is the failure of the idle air control valve. The IACV has coolant running through it, and the rubber gasket on the IACV fails after about 10-15 years. When this happens, coolant infiltrates the intake and fries the IACV, then the ECU. It could be something to check.

Do you know how to pull the plenum on this car? How about the IACV? Maybe just remove the rubber hose and open up the throttle body, and shine a flashlight inside? Are you having any idling issues?

I have the engine apart down to the Water control valve right now to replace it...

I have considered the possibility of the IAC leaking water... I might do the coolant bypass on it until I can afford to replace it (just in case)... I live in Texas and the temps won't be below about 70 until December so shouldn't have to worry about possible icing of the IAC...

It idles just fine and I don't have any codes on it so I am assuming it is working properly...

[Blindaviator]

Ok so just got the system put back together and started it up... Ran some prestone flush through the system for about 10 minutes... Was able to remove the bleeder cap while it was running without it pushing water from the radiator filler... Seems the water control valve was causing that...

Need to fill and drain the system one more time before filling it with coolant... Then the big test of is it still losing coolant...

Will repost when I know...