2001.5 PF overheating issue

[TheFatWolverine]

I have a 2001.5 pathfinder with a V6 3.5l engine, I'm sorry but I do not know what trim level it is. I have had an overheating issue for a while and am really stumped what could be causing it at this point.

So far I have replaced(including but not limited to the overheating issue)
Steering column
Lock cylinder
Battery
Starter
Idle control valve
swirl control solinoid
Cylinder 2 spark plug and coil
Mass air flow sensor
Radiator
BOTH thermostats
Water pump
Radiator fan clutch
Countless gallons of coolant

I am having unusual trouble bleeding the air out of the system and I know that is causing some of my grief, but it also begins to overheat if I turn the A/C on, but immediately cools back down if I turn the A/C off.

Additionally, if I start to go downhill it overheats almost instantly.

I know the head gaskets are fine, the oil looks like oil and not forbidden smoothie.

Thoughts?

[fixer3]

When you say “both thermostats” is one of those the coolant temp sensor?

[VStar650CL]

No, he means the Water Control Valve. The early VQ's had a separate 'stat to control flow through the block, while the main 'stat controlled flow through the heads and radiator. Nissan called the second 'stat the water control.

[fixer3]

OMG, I just finished watching a 4 part series of getting to that Water Control Valve. OMFG.

[mdmellott]

Thoughts?

When you first fill the the empty engine with coolant, place the heater temperature control in the maximum heat position, to be sure the lines to the heater core are open, and be sure the air relief plug is removed. Coolant should start flowing out of the the unplugged air relief hose. If nothing comes out of the hose, the hose is probably clogged which is trapping air in the system. This is the first step in filling the coolant system.

There are two coolant temperature sensors on your engine. The engine coolant temperature sensor on the block sends its signal to the ECM for engine controls. The other temperature sensor is connected to the same piping, at the back of the engine, that the air relief hose is connected. It's signal is sent to the temperature gauge on the dashboard. When you drive downhill, the trapped hot air rises to the highest point of the engine, which is that piping when you are driving downhill. Since the air is hotter than the coolant, your temperature gauge immediately reads as overheating.

* After slowly filling the cold engine with coolant until coolant flows out of the air relief hose, put the plug back onto the hose and continue to fill the system until coolant reaches the base of the radiator filler neck.
* Add coolant to the reservoir, up to the MIN or FULL COLD line.
* Wait 5min or so and recheck the coolant level in the radiator, adding more if necessary.
* Leave the radiator cap off and run the engine until the thermostat opens. (The upper radiator hose will become hot.)
* Rev the engine to about 2500rpm for 10sec then let it idle. Do this a few times.
* Turn the engine off and let it cool.
* Add more coolant to bring the level back up to the base of the filler neck.
* Squeeze the upper radiator hose to expel air, then add more coolant if necessary.
* Reinstall the radiator cap and add coolant to the reservoir if necessary.
* Start the engine, allow it to reach normal operating temperature and check for leaks.

These are the steps from my Haynes Repair Manual.
The Nissan factory service manual steps are similar but that has you putting the radiator cap back on before starting the engine and then repeating multiple steps until the coolant level in the engine stops dropping. (see page MA-16) https://www.nicoclub.com/service-manual ... 1%2Fma.pdf
I like the Haynes method better because it allows you to burp the system out of the open radiator and avoid having to repeat multiple steps and the FSM mentions nothing about setting your heater control to maximum, which is important to be sure air in the heater core is expelled and burped out. The choice is yours, but do it by the book. Either one.

[TheFatWolverine]

Where is that air relief hose?

[TheFatWolverine]

OMG, I just finished watching a 4 part series of getting to that Water Control Valve. OMFG.

Yeah, as soon as I saw where it was and how many things you need to remove to get to it I decided that one was way over my head and let the professionals deal with it.

[mdmellott]

Where is that air relief hose?

My bad. There are actually two air relief plugs that need to be removed.

[TheFatWolverine]

Where is that air relief hose?

Disregard, I missed the hyperlink you attached to the first time.

[TheFatWolverine]

first hurdle:

I don't know how to put in a picture here, my model appears to have not had the air relief plug installed in the front of the engine, and when I removed the rubber cap from the rear there was what looked like a sheared off bolt plugging the hose. is that supposed to be there, and how do I remove it without damaging anything?

[TheFatWolverine]

I figured it out!

[TheFatWolverine]

I figured it out! That vent filled up the end with rust, I just had to get a pick in there to break it all up and it flowed freely. now I'm bleeding it.

[mdmellott]

I figured it out! That vent filled up the end with rust, I just had to get a pick in there to break it all up and it flowed freely. now I'm bleeding it.

Excellent! I should have mentioned, not all models are provided with plugs at the front water pipe. No worries if it's not there. You just have to deal with the one in the back.

[TheFatWolverine]

To recap, I have a 2001.5 pathfinder with a 3.5l V6. I've been having issues with the cooling system, so far I have replaced the:
Radiator, radiator fan clutch, water pump, both thermostats, several gallons of fluid, I feel like there was something else but it's just not coming to me.

At this point I have(as far as I can tell) completely bled the system of any air. I can start the car from cold and run just fine. But anytime I stop, say at a stop sign, as soon as I start excellerating again and RPMs get above 2000 it begins immediately overheating. If I get it over 2000 while running cold everything seems to be fine.

Any thoughts on what could be wrong?

Also a quick rant:
I took this car to a shop to get the 2nd thermostat replaced, they said they had a really hard time bleeding the system. Well no kidding, they never opened the air relief valve! How do I know this? Because when I went to open it the hose was rusted shut!!

[mdmellott]

The only time I have seen the by the book procedure for filling and air bleeding the coolant system fail, was due to a failed head gasket allowing exhaust gasses to pass into the coolant system or the procedure steps were not followed to the letter. It's an easy chemical test to confirm a combustion leak by using any of the different brands of combustion leak test kits like this one. >>> https://www.amazon.com/Block-Tester-BT- ... B06VVBSFTF

[Rogue One]

To recap, I have a 2001.5 pathfinder with a 3.5l V6. I've been having issues with the cooling system, so far I have replaced the:
Radiator, radiator fan clutch, water pump, both thermostats, several gallons of fluid, I feel like there was something else but it's just not coming to me.

At this point I have(as far as I can tell) completely bled the system of any air. I can start the car from cold and run just fine. But anytime I stop, say at a stop sign, as soon as I start excellerating again and RPMs get above 2000 it begins immediately overheating. If I get it over 2000 while running cold everything seems to be fine.

Any thoughts on what could be wrong?

Also a quick rant:
I took this car to a shop to get the 2nd thermostat replaced, they said they had a really hard time bleeding the system. Well no kidding, they never opened the air relief valve! How do I know this? Because when I went to open it the hose was rusted shut!!

This is a continuation of an ongoing problem. While I realize that you're desperate to get things resolved, creating a new thread for the same issue is frowned upon. It's confusing and often counterproductive. Topics merged.

[Hawairish]

I'm in the same boat as you, TFW. Truck gets warm when it shouldn't and I've checked and replaced too many things. Right now my truck (04) is offline for a project, so I can't test anything further, but I will add that something I did to help with bleeding from the rear relief plug is I attached a clear vinyl tube to it and suspended it up a little before putting the end into a water bottle to act as a catch can. Ran the engine and could see bubbles coming out through fluid that partially filled into the tube...kind of like bleeding brakes. After two cool-heat engine cycles during the day, I felt confident I got the air out, but the issue persisted. The fact that bubbles were coming out in cycles also seemed to confirm the water pump was functional. And presumably, to mdmellott's last comment about exhaust gases, I guess the absence of more/perpetual bubbles is a really good thing!

I'll have to sniff around for the 2nd temp sensor mdmellott mentioned. My issue has been occurring for over the last year, and I've pulled, replaced, and tested everything except the radiator, water pump, and a 2nd sensor I'm not aware of. The rear sensor is actually on the crossover tube that houses the WCV, behind the passenger bank; the air relief tube is a separate tubing branch above the crossover that leads to the heater core. That sensor was tested on my stove with a thermometer and the resistance readings were spot-on with the FSM, so I think it's fine.

I'm going to flush my radiator when it's time to put it back into the truck, but I'm at a loss for this as well. At one point, I was actually getting a "engine temp too cold" which I had to install a 180F thermostat (OE is 170F). The 180F is from a VQ40, but I don't think putting a 170F back in helps here.

Btw, can confirm replacing the WCV is a pain. You gotta pull everything, and then look forward to coolant spilling into the top of the valleys atop the engine and trying to soak it all up as it seeps into all the dust and crud that's built up over the years.

General questions for VStar650CL and mdmellott:
1. What is even the nominal temperature the engine is supposed to be? Recently been using Nissan Data Scan to log things, and 220F is what my dash has been reading at mid-gauge (50%) but it's been warming up to about 75-80% which reads around 230F. That seems very high.
2. I'm aware most VQ35 (including the JDM R50) don't have the WCV. Neither does the VQ40. What harm comes from removing it?

[VStar650CL]

See LC-28 here:
https://www.nicoclub.com/service-manual ... 4%2Flc.pdf

On your '04, crack temperature on the main 'stat is 170F. It does have a WCV, crack temperature for that is 203F. The WCV on the VQ's basically limits flow through the block while still allowing flow to the heads and ancillary hardware, since the block is much slower to warm up than the top end. See LC-11 and LC-12 for the cooling schematics. On later R51's with an aux cooling fan, the fan kicks on low at 208 and high at 221, so I expect the ECM considers 230F to be pretty toasty. Have you checked out your fan clutch?

[VStar650CL]

PS - The harm from a missing WCV is insidious, it will evidence as increased cylinder wall wear over a long period. Wall wear is increased as much as eightfold at 90F compared to 180F, so a slow-warming block will accelerate the process.

[Hawairish]

Thanks, VStar. Yeah, was aware of the operating temps, so I presumed that if the engine is operating normally, I would expect temps just north of the 203F WCV temp. For sure 230F can't be good, but since 220F is about where I've always seen it (needle just under 50%) that seems expected.

The 170F thermostat spec is what bugged me the most. Mid 2022, I did about as much of an overhaul on my engine as I could. Pulled the transmission off to address an RMS leak, but also pulled the crossover pipe to replace its gasket. Tstat and WCV all replaced (knock sensor since it's hidden up there). Fan blade (excessive cracks) and clutch replaced, too. But for the t-stat, I initially replaced it with a 170F unit but the truck would throw a P0128. I eventually realized the unit it replaced was a 180F unit, so I put another 180F unit in and the issue went away. All t-stats (3!) and WCV were tested on the stovetop with boiling water and thermometer controlled by adding cold water as needed to drop down. They all checked out. Same with sensor.

At the moment, I suspect the clutch is not operating well because even when I know the truck is over-warm, it can be stopped relatively easily, and after small spikes while stopped, it will creep back down a little when accelerating. However, I've also gotten over-warm at cruising highway speeds while raining on 40F ambient nights...I wouldn't think the fan speed would matter at all in those conditions so it's why I suspect something else is up. Not sure it matters here, but I also added a transmission cooler in 2022. It's placed about 1.5" in front of the AC condenser, which is gapped about the same from the radiator. It does get warm, but I don't think it's heat soaking anything. I've stuck my hand in between to confirm airflow is not obstructed and all seems healthy.

FWIW, coolant mix is about as 50/50 as I can get. I buy a gallon of distilled water, a gallon of concentrate, and a gallon of 50/50...the first two go in, and I top off with 50/50.

Anyway, sorry to detract from the OP's issue with mine. Hopefully there's some correlation between the two. I'm at wit's end on my issue. My current project will require that I move the radiator 1/2" over, but since the fan shroud will need to be modified, I've been considering to go with e-fans to tackle this.

[VStar650CL]

You can check if it's an airflow problem pretty easily, and the clutch isn't hard to check either. For airflow, spray water on the radiator with a squirt bottle with the RPM's raised slightly. If the temperature plummets within a few moments then the coolant flow is good but the airflow isn't keeping up. If there's little drop or it takes a long time to show up, the problem is coolant flow and not air. Check the clutch with a heat gun or Bic lighter when the engine is cold. The fan should spin pretty freely when cold but develop a lot more resistance when you heat the bimetal spring on the front of the clutch. If the change in resistance is small or nonexistent, the clutch is leaked out and needs to be replaced.

[Hawairish]

I'll give the radiator a spray test when it's back on the truck in a few weeks. But to that extent, I expect that it's a coolant flow issue if cruising at 65mph in rainy 40F weather didn't produce a normal cooling condition. This event was before I bled excess out air, but the fact that the truck still got warm afterwards seems to counter that idea.

As for the fan clutch...I can give that a try. I've got a heat gun and fan's sitting in the parts bin at the moment. There's no leaking, unit still looks brand new...I bought it just over a year ago, maybe 3K on it. On cold starts, the fan roars (a good roar) initially from being dormant, then eases off a few seconds later once the fluid has circulated. I've had the truck over-warmed while idling in the garage and the fan didn't really seem to be spinning much faster/harder than at normal idle. I've also got a big floor fan that I've put right up against the front of the grille, full speed, hood open, and didn't see temp drops. That made it seem more coolant/flow related.

At times I still think it's the sensor, but it was tested. I don't see any reference in FSM for a 2nd sensor on my 04. Not that I want to throw any more parts at this, I do have my engine apart enough to easily swap out the water pump. Truck's 20 years old (I've had for 10) and it probably has the original unit still. I suppose it wouldn't hurt anything; it, the radiator, and the temp sensor are the only things I've not replaced.

[Buzzman]

I'll give the radiator a spray test when it's back on the truck in a few weeks. But to that extent, I expect that it's a coolant flow issue if cruising at 65mph in rainy 40F weather didn't produce a normal cooling condition. This event was before I bled excess out air, but the fact that the truck still got warm afterwards seems to counter that idea.

, the radiator, and the temp sensor are the only things I've not replaced.

You're telling us you haven't replaced it? That's one of the first things I'd do.
When I had overheating issues back when I had my 2002 Pathfinder, the first thing I did was replace the radiator. Fixed the problem.
If your radiator is original, go no further. Change it out.

[Hawairish]

No cracks, no leaks, and clean surfaces visible in all openings. I appreciate the input, but why would I replace the most expensive part first without proof of failure or defect?

I'm not saying it's not the problem or not due for replacement, but it wasn't on the roadmap for preventative maintenance at the time. My initial effort was to change the gaskets on the crossover pipe because I had the transmission off, and tackle the thermostats and coolant flush. PM seemed to have backfired on me because I put an OE-spec 170F thermostat and started throwing P0128 codes (engine temp too cold). Put an 180F back in when I realized that's what it had previously and then engine was running too warm (I live in AZ and never had overheating problems prior to this). Troubleshooting led to changing the fan blade and clutch; radiator cap was an easy swap. Fan shroud is intact. I installed a transmission cooler, and thought maybe it was a source of heat soak, but I also replumbed the transmission to the built-in cooler in the radiator and it made no difference.

It seems highly unlikely new parts are exploiting old parts here, but the costs of all those parts combined still cost less than a new radiator. That's why it's not been replaced yet.

[rgk]

I agree that the radiator could be causing circulation issues.The inside could be completely sealed up with rust, debris, and corrosion and you'd never know it from the outside. Check the temp difference between the top and the bottom hoses.

How long after bleeding were you getting bubbles out of your bleeder valve? If they're consistent or if you see them in your expansion tank, this strongly suggests a blown head gasket.

Have you tried testing the cooling system with a pressure pump?