VQ w/ possible blown headgaskets, how to be sure.

[CanuckQx4]

Hey guys, I am finally back and settled in my house and able to work on my 2001.5 Qx4. I put it away about a month ago when I believe the headgaskets blew, but I am not positive, and would like to be more sure before going balls deep in this project as head gaskets seem like a huge job on this truck.

When the truck overheated, the radiator basically exploded, aswell as a hose under the intake manifolds that connects the crossover tubes to the block. I was hoping I was lucky a month ago and changed those parts by taking all 3 pieces of the intake manifold off, and put it back together. The truck starts and runs PERFECT, but I noticed when filling the rad up, the coolant seeps right into the engine and fills the crankcase/oil pan with coolant as you are pouring it into the radiator neck.

Is this a sure sign of a blown headgasket, or could it possibly be a hose SOMEHOW connected wrong (even though I am sure everything went back where it came from) or possibly one of the intake manifold gaskets didnt seal properly?

How would you guys go about diagnosing this?

[Li'l Truckie]

For a head gasket, a quick and easy way is to remove the spark plugs to see if it wet and turn the engine over (no spark) and see which cylinder squirts out the anti-freeze.

Just don't be my dad and look directly in the spark plug hole! Kinda like off to the side.

A sure sign, don't know, you could have a cracked block or cylinder head. But regardless this problem sounds like a total teardown if the signs are not obvious.

Li'l Truckie

[CanuckQx4]

Thats the worst part, I dont even know how hot the car got exactly, I was standing inside the store just 30 feet away and left the truck idling because I was supposed to be 2 minutes. As soon as something let go and HEAVY steam started pouring from my hood, someone noticed, and her face was

So I ran out to the truck, thinking I possibly had an engine fire on my hands. (didnt notice the coolant lake around the tires) and I opened the driver door to get the keys out and pop the hood to find a mess of coolant from the radiator tank exploding. So ibought a new rad and installed, went to fill and noticed a coolant leak under the bottom intake manifold, took the intakes apart, fix hose, put it all back. Now when I fill the coolant from the neck it pretty quickly fills the engine oil with coolant

The truck currently sits flushed with new oil, and the rad completely empty, it runs and starts as normal, no white smoke (but theres no coolant in there to smoke mind you) ive only started it twice to flush the oil and move it into the garage.

I dunno why I have it in my head something is connected wrong and may not be headgaskets, How fast it fills the crankcase surprised me, I dont think a small headgasket failure could drink coolant that fast, its like it has a more clear path... make sence?

[Leo1998]

From my past experience with radiator coolant in the oil and accompanied with white smoke from the tail pipe, is a blown head gasket. Pull spark plugs and see which one appears to be wet or smells like anti-freeze. I wouldn't think putting those hoses back on would allow you to put them in the wrong order, unless you cut them all off and made new ones without labeling where they went, but still i can't see how the hoses would dump coolant into the oil pan. I also had a cracked block one time after forgetting to put anti-freeze in the radiator, just water. Went out to start next morning after a freeze and it just turned over and over without starting. It didn't even push the freeze plugs out, just a big hole in the block. Yours starts, so probably not a cracked block. If you discover it is the head gasket make sure you get the heads inspected and resurfaced at a machine shop, they will weld any cracks then make sure the head is flat, and not warped.

[CanuckQx4]

IF I end up taking the heads off they will definitely get serviced properly, I have a great local shop. Ive never messed with a timing chain so that may be tricky.

I also hear doing only one head gasket could be necessary? In a perfect world I would do both, but Im working in my garage and who knows how hard the exhaust manifold is going to fight me...

I guess I'll pull the plugs and see if it yields anything, but the truck has run for 2 minutes with no coolant in the rad so it may have dried and exhausted. id rather not fill the truck with coolant and have them mix if i can avoid that.

[Li'l Truckie]

Have you done a compression check? No since in filling it up with anti-freeze to see if the headgasket is shot. That's time and money wasted all over again.
Andy

[CanuckQx4]

I have a regular compression tester but not a leakdown tester. Will it be good enough?

I was going to do that after work tonight, just needed to research how to do compression check the motor without fudging up the ignition coils in the process, Ive only ever used this tester on my Honda which uses a distributor

[Li'l Truckie]

My guess is it should, a leak is a leak, and if so the compression will be different. Besides its only a little time and no money involved yet.

Ignition coils, check engine light, sorry I'm with you on this one...don't know . I'm old school, like vintage, I walk to and from school up hill both ways - distributor, points, condenser, rotor, carburetors, mechanical fuel pumps and positive ground.

[Towncivilian]

Compression test procedure is described on EM-14 of the FSM, but it looks like a pain in the a** for sure. I've never done one so I can't offer any more advice, sorry.

[Slumpert]

Unless you connected your heater lines into the valve cover vent tubes you could not cause this by hooking something up wrong.

[CanuckQx4]

As far as I can tell the valve cover vents are perfect, there was the one crossover hose at the front of the engine that vent from valve cover to valve cover, and also a vent on the backside of the drivers valve cover that feeds back into the intake, all connected proper.

Guess I will report back with compression test results as soon as I possibly can get into it

[Li'l Truckie]

Unless you connected your heater lines into the valve cover vent tubes you could not cause this by hooking something up wrong.

say it isn't so

However, I can easily seeing myself doing something like this. All those hose look the same, coolant, vacuum, air breather/emissions hoses, oil return lines. I remember putting the plenum spacer on my wife's FX35, and it's like, what are all of these hose for

And the wiring harness was just as bad. I had to disconnect the whole driver side wiring harness from the engine to replace the valve cover gasket. Needless to say, I left the passenger side valve cover gasket alone, so much more wiring to pull off and disconnect.

From your updates, I'm still going with bad head gasket.

[CanuckQx4]

Pulled all of the ignition coils, all 6 spark plugs everything at once and did the compression test cold and these were my numbers.

2- 185 1- 185

4- 185 3- 180

6- 180 5- 180



Pretty consistent. There was also no oil or milkshake on any of the plugs (mind you the engine isnt filled with coolant right now)



Does anyone have insight on the intake gaskets, does coolant pass through them? Mainly the bottom gasket that attaches the intake to the block, it was the sturdiest gasket and each port was rubber oringed. But I dont remember seeing a coolant passage.

The ammount of coolant it will drink into the engine is just to fast for me to think its guzzling it through a small head gasket failure, when i was filling it when this first happened it swallowed 3 gallons in a few minutes before I realized something was severely wrong and pulled the dipstick.

[Leo1998]

Wow! nice job on the compression test. This may help in figuring out the coolant flow for your rig and see where it's going. http://www.jimwolftechnology.com/wolfpd ... _bolts.pdf

Also something else of interest, It says "leak" so not sure how much, but it found a way into the engines oiling system. http://airtexwaterpumps.com/wp-content/ ... -Leak1.pdf

[CanuckQx4]

That link for the TSB certainly adds mystery onto how the coolant could be getting into the oil, but If im reading it right, it would leak out a weeping hole at the same time?

I was not noticing any EXTERNAL leaks when refilling the coolant.

[Leo1998]

This diagram is better. http://www.nicoclub.com/FSM/QX4/2000/LC

[CanuckQx4]

that link isnt working for me bud. I just pulled the OIL COOLER off, the hoses desperately need to be replaced, they are very mushy.

Id love if I could sort this out and the end result not be a blown headgasket. Im ready to fix whatever it may be, but Id hope to be certain before pulling heads off

[Li'l Truckie]

With those compression numbers, I'm a little stumped. One should have been different unless you have a crack between a cooling gallery and a oil feed line and not around a cylinder. In this case no antifreeze would make it into a cylinder, it would just mix together between due to the pressure of the two systems where you have the crack in the head gasket. And if this is the case, no telling if its the right or left head gasket.

[CanuckQx4]

That tsb for the waterpump linked above sounds pretty fishy aswell. Im not sure if I totally understand it, the waterpump on the VQ35DE is like nothing Ive seen myself before

[CanuckQx4]

And look at this video I found of a seemingly professional mechanic doing a water pump job on the VQ, skip to 3:40 where he talks about the blown seal and people thinking they have blown headgaskets

http://infinitihelp.com/diy/common/infi ... cedure.php

What are the odds this could be my problem?

Even though a water pump job doesnt seem like any small task either!

[Leo1998]

Oh... that would suck to do the head gasket and put it back together to find out it was the water pumps seal. Might as well do the timing belt too... Wonder if a coolant circuit leak tester can determine if it is a water pump seal.

BTW: I would research that some more, it did say there would be leaking around the thermostat housing if it failed.

[CanuckQx4]

Ya the way the mechanic says in that video that people replace the HG by mistake it makes it seem like a common problem, yet I find no info while searching, tried an hour on that topic.

I did not NOTICE any leaking from the weep hole, but I just pulled it out of storage after sitting for a year (periodically started) and did a transmission overhaul on the thing, and about 1000miles later this happens

[Slumpert]

If the comptession is that good and the internal leak that bad then I suspect it is a cracked coolant passageway. You did have a steam explosion so it certainly is possible that interal damage is present.

Start by checking the water pump, as most of those steps need to be done to pull the engine anyways which I expect your going to endup doing.

[CanuckQx4]

Ya I am going to pull it in the early afternoon, do you guys think the oring will be completely split if thats the failure? Or could it be more subtle?

A new pump/tensioner is only $120, I would love if luck would help me out just this one time!

[Slumpert]

You just need open the pump access panel and then attempt to fill the coolant system. At this point might as well just be using distilled water.

Your looking for water coming out of the pump so stuff rag under it and see if it starts absorbing water.

If what you can see keeps dry.. then it is not a leaking pump.

[Leo1998]

I agree with Slumpert, you will have to tear it down to the heads, go after the water pump first and check the o-ring seals. I think it would be a visible failure of the o-ring, if fluid is allowed to pass.

I was wondering if there is a way to diagnose the water pump o-ring by pouring water/coolant through a different opening away from the water pump and see if you still lose water/coolant with the rig not running. Maybe a funnel with a hose connected? Pour the water in and see if the level remains constant, if it does then not the Head Gasket and is the water pump o-ring seal. If it doesn't stay level then the head gasket is leaking. Does the circuit have to be pressurized to get a result? Idk. Will gravity alone give a result of a bad head gasket leaking? Something to think about.

Read: http://www.brakeandfrontend.com/Article ... ement.aspx

[CanuckQx4]

Well I managed to pull off the fan shroud, fan and the belts, aswell as the tensioner and water pump covers. I was going to try filling it and looking for the leak at the pump but there really is no visibility at all the pump is so sunk back into the engine.

Getting that tensioner out of there and slacking up the chains is scary business! I seemed to do it just fine and followed the video i posted though.

I ran into a road block though as I dont have any long M8 bolts to extract the water pump, off to the store I go! I'll post a pic of the pump when I get it out

[CanuckQx4]

Waterpump o-rings are intact, all the coolant behind the pump looked brand new fresh aswell, no sign of any milk shake back there..

I was really hoping the rings were going to be cooked. Hoping to find the smoking gun. Should I order the water pump and change it first anyways?? No matter what its getting a new pump, but it takes 3 days average for my nissan parts dept to get parts, so I either order a new pump and wait and try that first... or assume the worst and order all the parts needed for the full headgasket

How can I pinpoint the leak to ensure I have a headgasket failure, hopefully with a tool I have or can buy cheaply and do myself.

[4xq]

Hate to say it, but you are pretty much at the end of the testing.

The water pump is the last possibility for a leak into the engine aside from a major failure. At this point, if you put the new water pump in, you know its good. So I would drain the oil, and leave the drain plug out. No need to reattach the oil cooler stuff, just block off the hose openings. Reattach all the cooling hoses, and fill the cooling system with water.

If water starts coming out the oil drain plug hole, there are no good choices left. If the cooling system holds water, you got lucky.

If the cooling system still leaks into the engine, there are three possibilities:
1. Bad head gasket.
2. Cracked water jacket in a head.
3. Cracked water jacket around a cylinder in the block.

The only way to figure it out at that point is an engine teardown.

I think the smoking gun may be a thermostat that stuck closed. Thing is, the VQ35DE in the Pathys / Q's is weird because it has two. The front one by the water pump, and the "water control valve" in the back, which is a thermostat, which attaches to the hose in the back of your engine that blew. If you look at the diagram Leo1998 linked to at jimwolftechnology.com, the cooling diagram shows that the water control valve affects cooling in the lower engine block. If it sticks shut, that will cause overheating in the block.

That would be my read on it, anyway. I've rebuilt a few engines over the years, but not a VQ35. I have not seen a thread on failure of the rear thermostat ("engine control valve"), so I'm making my best guess here,

You can test the front thermostat in hot water and see if it opens properly. If it does, I think the rear thermostat will be stuck closed.

Heres hoping for lucky!

[CanuckQx4]

Ok sounds like I will place the order for the water pump tomorrow, I could buy one from autozone an have it in my hands tomorrow, or wait til probably monday for an oem one if I go that route.

install that, fill the coolant and hope it doesnt go in the crankcase...

To me if this was a headgasket breach though, the coolant would seep into the crankcase SLOWLY, it drinks from the rad quite quickly.

I just read the cylinder head removal steps in the fsm, step 1, remove engine from vehicle... FML, I cant do that in my garage