2002 Pathfinder Overheating! Help!

[jmatthi]

My 2002 Nissan Pathfinder had an oil leak and I discovered the level to be low. I took it to my mechanic and they fixed 2 leaks that they discovered after a top and bottom steam clean. about a week later it overheated while going over a mountain pass. I stopped and let it cool, topped off the oil (turns out they didn't do an oil change like I expected when they fixed the leak so it was low to begin with), then it was able to continue the rest of the trip.
I brought it back to my mechanic when I got back. They got a large temp differential between top and bottom hose from radiator so concluded that it was a thermostat issue. They replaced the thermostat and the water control valve (sometimes referred to as the "second thermostat"). I question the need for this to be done... I get my rig back and within 10 minutes on the hiway it is overheating again, I immediately bring it back to the mechanic.
They perform further diagnostics...and finally conclude that it is a head gasket. Although there were no symptoms of a head gasket being blown other than the overheating. Radiator checks out, fan is good, thermostat(s) are new, coolant is clean, oil is clean, hot air pumps from cabin heater, doesn't overheat at idle, hoses are good... they performed a test where the coolant turns from green to blue indicating hydrocarbons present and that to them was a 100% certainty that the head gasket was compromised. They wrote up a quote for over $5k to replace the head gasket, or $400 to use a "head gasket repair" additive treatment. I opted for the additive, as I have no plan to sink
that much $$ into this vehicle with 160k miles.

My question is: I have found through searching the web other similar scenarios, but no definitive answers or resolutions... especially from Nissan or Nissan Technicians. I would really like to figure this thing out... is it really the head gasket? if so, how come it is not blowing smoke/water? why is the coolant and oil so clean? and engine runs perfectly? what are we missing???

Thanks so much! Love the pathfinder, but this has been real hard (stress and $$$)

[Hawairish]

Why? Because you need a new mechanic.

Head gasket...yeah, if your fluids are clean, it's not your $5K head gasket. (BTW, you could pay for a rebuilt motor to be swapped in for less!) Did they really change the water control valve? The same thing at the very back of the engine that requires a decent amount of labor just to get to, let alone replace? Did they even put coolant back in? (Serious question since they couldn't put oil in after repairing a leak..or perhaps not repairing a leak and that's why you were low again.) Did they introduce air into the coolant system and not cycle it through a few times?

How did they test the radiator? Pressure test (if so, why)? Did they flow anything through it? Is radiator cap working, is there coolant in the overflow reservoir, and is that reservoir leak free?

Are you sure that the coolant they tested was even from your truck? Did you see them fill up a container and test it in front of you? A couple drops of fuel or injector cleaner in anti-freeze...boom, hydrocarbons. Have you verified the test's validity? You can buy kits to test it yourself. If they changed out the coolant (doubtful), then the amount of hydrocarbons should be extremely diluted.

Has the coolant ever been changed? Was it a 50/50 solution? Did they just top it off with undiluted coolant or water? Perhaps it's just a coincidence, but maybe the water pump fins have corroded and the pump has lost efficiency.

I'd also check the fan and fan clutch. Hot air isn't really indicative of any function; if the engine is warmed up, you'll have hot air regardless.

If you haven't already, I HIGHLY suggest reading through the MA and LC chapters of the FSM. That will tell you just about everything you need to know about your cooling system and how to test it.

These guys sound like clowns. There are still plenty of things to check before a $5K head gasket. I think your mechanic is prepping for a wonderful Christmas...

[Buzzman]

Have to agree with Hawairish.
First thing would be to stop going to your mechanic. Find another one, or take it to a dealer for a proper check.
I doubt that these guys replaced the "second" thermostat as well. It's a major job and would be expensive and time consuming.
Head gaskets on these engines rarely, if ever fail BTW. They are bullet proof.

Looking back on your first statement, that the lower rad hose was considerably colder that the upper one, leads me to believe you need a new rad.
I had a similar situation last year, and a new rad, main thermostat and some hoses fixed the problem.
The thermostat and hoses were replaced as a preventative measure at my request. They were still functional, but I felt it was worth replacing while the rad was out.
Keep us posted.

[Hawairish]

Yeah, as soon as I saw the note about the water control valve, I thought, "No way they changed that". You have to pull off the intake manifold, de-pressurize fuel rail, and disconnect a ton of other stuff just to see the valve. What'd that bill cost anyway?

I was thinking about the temperature differential, and I read it like they ruled out the radiator because of that. I mean, you should see a temp diff...it means the radiator is working. If coolant wasn't circulating through it, I'd expect both hoses to be about the same: hot. Jmatthi, can you clarify that part?

[jmatthi]

They did replace the water control valve, as to the cost... it was a bit over a grand for: diagnostic, replace thermostat, and water control valve(biggest part of the bill), (plus a few minor things, I'm sure).

Sorry I don't think I can clarify too much about how they tested the radiator. I think that the temp differential between the hoses was a part of the diagnostic which initially led them to believe it was a thermostat issue. They replace the Tstat and WCV and still overheated on road test. Then they tested for combustion gases in the cooling system - got a positive result and it was all about the head gasket from there.

I asked them about their procedure for bleeding the cooling system as I had read that the NP can be tricky to bleed properly. They had read up on it and were confident that it was bled properly.

[Hawairish]

I still think they really jumped the gun on changing out the WCV, of all things. I mean, that's way down the diagnostic tree in my opinion. The thermostat, sure, but only after checking the water pump and radiator. You didn't mention any diagnostics on the water pump...the heart of the system.

Even worse is that you forked out that much money to have them not only incorrectly diagnose the problem, but perform unnecessary work. To me, that's a poor shop.

You need to at least get a 2nd opinion from another shop. In doing so, I would initially refrain from telling the new shop what work was recently performed (I'd tell them about the thermostat, but that'd be about it)...the gamble is that if you say "my last shop said I needed a new head gasket", then they'll be inclined to agree. Just tell them the symptoms, what's been checked (believe me, they'll still check) and have them draw their own conclusions.

You really need to check the LC chapter of the FSM if you haven't already.
http://www.nicoclub.com/FSM/Pathfinder/ ... der/lc.pdf

[jmatthi]

I agree that they charged me too much for repeated hasty diagnostics but the symptoms are/were challenging to say the least, and I think I did a poor job (as a customer/consumer) in doing my homework and due diligence. I am taking it as a lesson learned, I have already commited more money than I should have. As of now the truck is still running great and no overheating - I commuted to work and back without incident. It is not a long commute but does involve both in town driving and highway speeds. At this point, for this vehicle it is more about the mystery - as I do believe they honestly did their best as that has been my experience with the shop. I would love to hear from a Nissan technician about what they've seen/experienced with this sort of scenario...
Thanks for your feedback, it is appreciated. I have contact info of an independent mechanic that is highly recommended by a lot of people at my workplace, so if I do need (and finances can recover) I'll have him take a crack at it. I fully intend to take more of my car care into my own hands from this point forward. I will definitely check out the FSM, thanks for the link!

[nalz]

If i missed it somewhere, i apologize, but i did not see what was the repair that finally got your truck running great. Was it the head gasket? How much $$$, if you don't mind?

[jmatthi]

That is one of the puzzling things, it has never stopped running great... but under load ( mountain pass, freeway speeds) it would overheat. I was presented with 2 options: replace head gasket - their total quote was @5k, or try a head gasket sealer additive since it was seemingly a small gasket leak that only presented itself under load. I am far from convinced that "all is well", only time will tell, but so far so good.

[Hawairish]

It's a pretty expensive lesson to learn, unfortunately (I have some family members who seem to learn that annually). Even if you trust your shop, and even if they seem like really nice people, you should still always get a 2nd opinion (even if it's your own). I mean, what's worse: a shop deliberately trying to sell excessive services or a shop unable to properly diagnose a problem? I don't differentiate the two when it comes to choosing a mechanic.

Now, in all fairness, I'm not saying your mechanic is either or both, given your previous comment about the shop...but it's something you should always keep in the back of your mind, especially when it comes to high repair bills. I mean, think about that $5K head gasket...if your insurance company had to shell out $5K for a repair, they'd just total the vehicle.

You should consider checking out NPORA and posting there if you haven't already. Many guys there are either former or current Nissan technicians, service managers...we even have a resident parts guy.

Can't stress it enough...check the FSM. These are what Nissan mechanics use. There's even a part of their symptom matrix that covers non-cooling causes of overheating. Have you visually checked for any obstructions to the radiator, damaged fins, the fan clutch? These are important parts. You mentioned overheating while both on highway (presumably cruising speed, and low load) and through a mountain pass (high load). I'd expect it under high load, but not cruising speed...what are your RPMs? Have you taken a OBDII scanner to check any diagnostics?

[jmatthi]

[quote="Hawairish"]
I mean, think about that $5K head gasket...if your insurance company had to shell out $5K for a repair, they'd just total the vehicle.

That is why I did not authorize that repair... I hit my limit and am done with them and my Nissan. Anything further work will be scrutinized much more so. I don't think they did a great job, but not negligent either. I think that more mechanics would have had trouble with figuring it out than not.

[01pathfinder7]

Were your mechanics firimilar with the pathfinder. Did they bleed/burp the air properly. There is a small tube sticking up at the mode back of your engine to let air out of the system.

I need to do this to mine in fact and was wondering if anyone has the best tutorial for this.

I did I remove the plug today and had someone Rev the engine to 2300rpm on and off. Sometimes coolant would flow other times it stopped and then would start again. Would a constant flow mean no air. If so there is likely more air in mine as it reminded sporadic.

The truck was parked up on a curb for this to lift the front. Only about 20cm. Is more needed?

[Hawairish]

I hit my limit and am done with them and my Nissan. Anything further work will be scrutinized much more so. I don't think they did a great job, but not negligent either. I think that more mechanics would have had trouble with figuring it out than not.

If I ever have a shop that not only doesn't do a great job AND doesn't solve the problem I've paid $1K for (or whatever you've paid already), "negligent" is exactly the word I'd use for them.

You've not really answered any of my questions. Do you want help or not? Have you looked at the FSM at all yet?

You do realize that one possible cause of overheating is air in the system, and that purging the air requires little more that running the engine a couple times and checking the reservoir? This is spelled out in a single page in the FSM. It's a completely tool-less process. Seeing as your mechanic replaced things, has issues topping off fluids, and is probably unfamiliar with the truck, seems like a no-brainer to me to try to rule something out.

[jmatthi]

Hawairish
Internet service has been out for a few days... I'll try to answer your questions...

radiator is clean, no obstructions to be found.
mechanic tested fan clutch - and it checked out fine.
it is not kicking out any codes.

I do have the FSM now, thank you and have been looking through it. From what I can tell, at this point it is either the head gasket (as the shop is convinced) or the water pump.

regarding bleeding/burping the system...
From my earlier post
"I asked them about their procedure for bleeding the cooling system as I had read that the NP can be tricky to bleed properly. They had read up on it and were confident that it was bled properly."

I just took it in to them for a "courtesy" follow up, as they wanted to do another flush of the system. they spent 2.5 hrs flushing, filling driving, burping and repeating - using the proscribed procedure from Nissan.

01pathfinder7 - they lifted the front of my rig @1 foot.