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Nissan Pathfinder heat issue

crispins

crispins

FJB
Joined
May 21, 2020
Member Number
846
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1,640
Loc
Pigeon Forge, TN
I posted on the Pathfinder forum last year and got no expertise there so perhaps you fuckers can figure this out.

2005 Pathfinder 4.0 VQ engine.

Had this for about 2 years now, engine runs perfect, does not use a drop of coolant.

Fucking heat is not there.

I can bled the system (nose up on a hill, lid off expansion tank, rev over 3k for 5 mins or so) heat will get burn you out hot.

For the next few days it is pretty hot then it gets cold and will not get hot again until I bleed it again.

Blend doors are functioning correct.

It seems that air gets in the system and reduces / stops flow to the heater core.

This truck does have the rear heat and a fuck ton of piping for the heater cores.

I have heard of a "seep" before which is a tiny leak somewhere that allows air into the system.

This is my winter vehicle so heat is important.

I have not pressurized the system with a tester yet, should that be my next step?

So far I have changed the thermostat, checked the coolant booster (it works), and currently covered 2/3 the front of the radiator with cardboard.

Nothing makes a difference except for bleeding the system, that is the only thing that makes a difference.

Thoughts?
 
Take the heater core hoses off and flush them with a hose.
I don't know about Nissans, but Chevys seem to plug heater cores.
 
welndmn said:
Take the heater core hoses off and flush them with a hose.
I don't know about Nissans, but Chevys seem to plug heater cores.
Click to expand...

This worked for my 2005 f150. I changed the water pump just out of precaution and I must have stirred some stuff up because the heat was really weak after. I took off the lines and back flushed it with a water hose. A small amount of sediment came out but after I did this the heat worked great.
 
welndmn said:
Take the heater core hoses off and flush them with a hose.
I don't know about Nissans, but Chevys seem to plug heater cores.
Click to expand...

I feel like if the core was clogged then bleeding would not make it hot as fuck again are my thoughts.

However, I can give that a try.

I haven't wanted to mess with the brittle plastic manifold that the heater hoses are connected to as I hear they break then it is a super PITA to fix.

This is what the manifold looks like

51N27LbiRcL._AC_SL1200_.jpg
 
is there a front heat only part that you can replace that great big mess with and just delete the entire rear heat system?

that's what I used to do on the chrysler vans when that shit would all start to leak. was 1/3 the price, didn't fucking suck as bad.
 
If the coolant is getting displaced by air wouldn't the coolant level rise? Is that happening? Bypass rear shit as the manche suggested.
 
Do these systems have a vacuum actuated heater control valve? (maybe the thing in upper right corner of pic?) I deleted the one on my XJ with 2 pieces of hose, no problems since.
 
I have one of these and have experienced the same thing. Mine only did it maybe once or twice but I think I just took that nipple off the heater line somewhere on the passenger side by the firewall. Same as yours it gets air in there yet doesn’t use coolant.

I guess if yours does it more often put a valve on it so you can just crack it open and shut it every now and then. Fuck fixing the actual problem when you can redgreen that shit.

One word of advise on these Pathfinders. If they have a check engine light on fix it right away. I got mine from my ex who had let the cels stack like crazy. It ended up plugging a cat and all that unburnt fuel backed into the engine and washed the bearings. Knock knock knock goes the VQ40 now. A very reliable engine that should have lasted 300k+ now gone to neglect at 150k.

Im going to fix it though. With a Diesel.
 
In my experience a heater core not heating up is the first sign of a head gasket issue. No idea what vehicle your having issues with but it’s the first place I look.
 
I agree with the restricted heater core theory, but in the image you posted of the water manifold it appears to have some valves installed in the system. Those valves could also be faulty and stuck closed. I am not familiar with your particular vehicle, but other mfrs use similar systems.

Check the hoses going in/out of heater core, if you can get your mitts back there you can do it by feel, or if you have a infrared heat gun you can check with that too. Heater Inlet hose should be hot and the outlet hose should be almost as hot. If inlet is hot and out is cold you have clogged heater core. If both are not hot then likely failed/clogged/restricted valve
 
crispins said:
I posted on the Pathfinder forum last year and got no expertise there so perhaps you fuckers can figure this out.

2005 Pathfinder 4.0 VQ engine.

Had this for about 2 years now, engine runs perfect, does not use a drop of coolant.

Fucking heat is not there.

I can bled the system (nose up on a hill, lid off expansion tank, rev over 3k for 5 mins or so) heat will get burn you out hot.

For the next few days it is pretty hot then it gets cold and will not get hot again until I bleed it again.

Blend doors are functioning correct.

It seems that air gets in the system and reduces / stops flow to the heater core.

This truck does have the rear heat and a fuck ton of piping for the heater cores.

I have heard of a "seep" before which is a tiny leak somewhere that allows air into the system.

This is my winter vehicle so heat is important.

I have not pressurized the system with a tester yet, should that be my next step?

So far I have changed the thermostat, checked the coolant booster (it works), and currently covered 2/3 the front of the radiator with cardboard.

Nothing makes a difference except for bleeding the system, that is the only thing that makes a difference.

Thoughts?
Click to expand...


the rear hoses leak. You can cap them by the firewall on The passenger side. That should fix your problem.
 
87manche said:
is there a front heat only part that you can replace that great big mess with and just delete the entire rear heat system?

that's what I used to do on the chrysler vans when that shit would all start to leak. was 1/3 the price, didn't fucking suck as bad.
Click to expand...

Nothing that I have read but I am going to study the routing and see what kind of bypass I can come up with.

Thatg9659 said:
If the coolant is getting displaced by air wouldn't the coolant level rise? Is that happening? Bypass rear shit as the manche suggested.
Click to expand...

That is a pretty good point. I think my next step will be to bleed the system again, mark on the expansion tank the coolant level, and recheck that after the heat goes away again and see if it has risen.


Riles said:
Do these systems have a vacuum actuated heater control valve? (maybe the thing in upper right corner of pic?) I deleted the one on my XJ with 2 pieces of hose, no problems since.
Click to expand...

No valve, uses a booster pump to help move coolant around the 40' feet of coolant lines. last year I verfied that the booster was working, will look into that again this year.


KungFooMASTA said:
I have one of these and have experienced the same thing. Mine only did it maybe once or twice but I think I just took that nipple off the heater line somewhere on the passenger side by the firewall. Same as yours it gets air in there yet doesn’t use coolant.

I guess if yours does it more often put a valve on it so you can just crack it open and shut it every now and then. Fuck fixing the actual problem when you can redgreen that shit.

One word of advise on these Pathfinders. If they have a check engine light on fix it right away. I got mine from my ex who had let the cels stack like crazy. It ended up plugging a cat and all that unburnt fuel backed into the engine and washed the bearings. Knock knock knock goes the VQ40 now. A very reliable engine that should have lasted 300k+ now gone to neglect at 150k.

Im going to fix it though. With a Diesel.
Click to expand...

Yes there is a nipple there on that manifold I posted above, I used to use that to bleed but found that it will bleed by itself if you take the lid off the expansion tank and run it like that.

Dunny enough the check engine light doesn't work, I connect my scanner to it occasionally, I always get the same codes, cats inefficiency and EGR. I really want to get rid of the pre cats on the manifolds as I feel like they are likely clogged and fucking with the MPG. This truck i bought at auction for $1,200 almost 2 years and 15k miles ago. It owes me nothing but it is really nice and I use the shit out of it. I would like it to last for a few more years and the heat is the only issue I have with it.

ThePanzerFuhrer said:
In my experience a heater core not heating up is the first sign of a head gasket issue. No idea what vehicle your having issues with but it’s the first place I look.
Click to expand...

I know, I feel the same. However 2 years, 15k miles, not a drop of coolant used, never any mix with oil. It cannot be a head gasket or I would be adding coolant.

Fishnbeer said:
I agree with the restricted heater core theory, but in the image you posted of the water manifold it appears to have some valves installed in the system. Those valves could also be faulty and stuck closed. I am not familiar with your particular vehicle, but other mfrs use similar systems.

Check the hoses going in/out of heater core, if you can get your mitts back there you can do it by feel, or if you have a infrared heat gun you can check with that too. Heater Inlet hose should be hot and the outlet hose should be almost as hot. If inlet is hot and out is cold you have clogged heater core. If both are not hot then likely failed/clogged/restricted valve
Click to expand...


I remember last year using my IR to check temps and thinking it was fine but I will redo that as well. No valves in the heater lines at all. Hot coolant always goes through the heater cores.

Ugly pumpkin said:
I agree. Leak down test cylinders and check cooling system.
Click to expand...

I will pressure test coolant system and see what that does. I do not have a cylinder test kit and do not think that would be needed right now being that the truck hasn't used a drop of coolant in 2 years, is that wrong thinking?
 
Most of the time with modern engines with mls gaskets, head gasket leaks are combustion gasses being pushed into the cooling system causing excess pressure and vapor lock issues. First symptoms are unreliable heat output and over heating on very long journeys because the excess pressure usually pushes alot of coolant into the expansion tank on a closed system. Since Nissan uses a degas tank, you usually will not have over heating issues but will get lack of heat due to all of the combustion gasses stuck in the heater core and lines.
 
Coolant pressure tests I do in no particular order.

1. Pressurize system cold and look for pressure drop and leaks.

2. Get engine up to temp with cap off. Pressurize system and look for pressure drop and leaks.

3. Attach pressure gauge to system cold and get engine up to temp to ensure its building pressure.

4. Verify system is coming up to temp.

5. Drink beer and scratch head.
 
yozsi said:
Most of the time with modern engines with mls gaskets, head gasket leaks are combustion gasses being pushed into the cooling system causing excess pressure and vapor lock issues. First symptoms are unreliable heat output and over heating on very long journeys because the excess pressure usually pushes alot of coolant into the expansion tank on a closed system. Since Nissan uses a degas tank, you usually will not have over heating issues but will get lack of heat due to all of the combustion gasses stuck in the heater core and lines.
Click to expand...

If this is happening can you re torque the head bolts or do you have to change the gaskets?
 
yozsi said:
Most of the time with modern engines with mls gaskets, head gasket leaks are combustion gasses being pushed into the cooling system causing excess pressure and vapor lock issues. First symptoms are unreliable heat output and over heating on very long journeys because the excess pressure usually pushes alot of coolant into the expansion tank on a closed system. Since Nissan uses a degas tank, you usually will not have over heating issues but will get lack of heat due to all of the combustion gasses stuck in the heater core and lines.
Click to expand...

This right here. Cylinder leak down test should verify. Little coolant loss, low operating temps, no heat. Slow pressure loss during cooling system pressure test. (I think.)
 
yozsi said:
Most of the time with modern engines with mls gaskets, head gasket leaks are combustion gasses being pushed into the cooling system causing excess pressure and vapor lock issues. First symptoms are unreliable heat output and over heating on very long journeys because the excess pressure usually pushes alot of coolant into the expansion tank on a closed system. Since Nissan uses a degas tank, you usually will not have over heating issues but will get lack of heat due to all of the combustion gasses stuck in the heater core and lines.
Click to expand...

Well damn, that would make sense as too what it is doing.

The truck has no issues driving long distances.

Got any ideas how to get heat out of it, drive during the winter with the degas cap off?

This is a really nice truck, looks almost brand new, interior is a 9/10.

Not worth paying someone to put a used engine in it.
 
Thatg9659 said:
If the coolant is getting displaced by air wouldn't the coolant level rise? Is that happening? Bypass rear shit as the manche suggested.
Click to expand...

If it's a simple leak, no. The engine warms up and builds pressure. Coolant leaks out the leaky parts and the amount of coolant in the system decreases. If to much coolant leaks out, the engine will overheat, temps and pressure will spike and remaining coolant/gasses will blow out the relief valve in the radiator cap.

If it just leaks a little, when the engine is shut off and cools, the gasses that displaced the leaked out coolant will contract to the point where it puts the system in a vacuum and draws coolant from the reservoir until the system is full.

Maybe. Im day drinking.
 
M92PV4U said:
If this is happening can you re torque the head bolts or do you have to change the gaskets?
Click to expand...

I have never heard of anyone doing that. Let alone having success with it. Head gaskets get physically damaged when they fail. Very different than a valve cover gasket that may stop seeping after a snug up.YMMV.

Recent head gasket job.
20200919_152756.jpg
 
Ugly pumpkin said:
I have never heard of anyone doing that. Let alone having success with it. Head gaskets get physically damaged when they fail. Very different than a valve cover gasket that may stop seeping after a snug up.YMMV.

Recent head gasket job.
Click to expand...

I don't think that is would work on that gasket either. I was just thinking if it's mls gasket maybe they leak between the steel layers.
 
M92PV4U said:
I don't think that is would work on that gasket either. I was just thinking if it's mls gasket maybe they leak between the steel layers.
Click to expand...

I doubt they would fair better. I would assume the combustion pressure and temp would cook them as well. But I have no first hand experience. Maybe yozsi can chime in.
 
I am going to perform the exhaust gas in coolant test and if it comes up positive (which I think it will) then I will just buy a winter car

it seems like the most economical choice to me.

Some reliable shitbox that is fully depreciated, park it for 9 months of the year drive it in the winter.

Fixing this truck does not seem like it would make the most sense.

Head gaskets are a fucking nightmare due to all the timing chains and specialty tools needed to get it timed correct. (If I am wrong here tell me, I have done at least a dozen 4 cyl headgaskets, never a v6)

Plus this engine has 200k miles on it, I can't see how it is worth it to open it up

A used motor is a crap shoot, they are around $1,500 plus the labor (I am not doing it) so $2,500 and who knows if it will be any better than this one.

Who know how much longer the truck will drive like this, honestly the truck drives great, smooth - no issues.

Am I being stupid here?


*Edit* I am also going to experiment if the truck can be driven with the degas lid off, my theory is it would self bleed that way and let the heater core keep flowing?
 
Last edited:
crispins said:
I am going to perform the exhaust gas in coolant test and if it comes up positive (which I think it will) then I will just buy a winter car

it seems like the most economical choice to me.

Some reliable shitbox that is fully depreciated, park it for 9 months of the year drive it in the winter.

Fixing this truck does not seem like it would make the most sense.

Head gaskets are a fucking nightmare due to all the timing chains and specialty tools needed to get it timed correct. (If I am wrong here tell me, I have done at least a dozen 4 cyl headgaskets, never a v6)

Plus this engine has 200k miles on it, I can't see how it is worth it to open it up

A used motor is a crap shoot, they are around $1,500 plus the labor (I am not doing it) so $2,500 and who knows if it will be any better than this one.

Who know how much longer the truck will drive like this, honestly the truck drives great, smooth - no issues.

Am I being stupid here?


*Edit* I am also going to experiment if the truck can be driven with the degas lid off, my theory is it would self bleed that way and let the heater core keep flowing?
Click to expand...

Exhaust gas in coolant test?

You can run it with the cap off. With no pressure in the system it will boil/overheat at a lower temp. Easy enough to try.

If it runs good, T into lower radiator hose to booster pump.
 
Ugly pumpkin said:
Exhaust gas in coolant test?

You can run it with the cap off. With no pressure in the system it will boil/overheat at a lower temp. Easy enough to try.

If it runs good, T into lower radiator hose to booster pump.
Click to expand...

download.jpeg
it checks for combustion gasses in the coolant.
 
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