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Discussion Starter · #1 ·
Hi Folks,
Before I go off ,and spend a bunch of money for nothing I thought I'd ask here. Yesterday I turned on the heat for the first time this fall. (2008 Frontier, 4.0 V6) I noticed it wasn't getting warm ,and I had a faint smell of coolant. It wouldn't defog. It was fogging. The only time I got any heat is when I was going up a hill. I checked the coolant ,and it was low (still is) I added about a third a gallon to the radiator ,but didn't have any left to fill the reservoir. I then parked it on an incline so the front was high above the back ,and turned the heater on full for awhile. Heat seemed to come back ,but of course the smell ,and fogging were still there. I drove to a local parts store for more coolant. I noticed where I had parked was a puddle of coolant. When I got back I lifted the hood to look for leaks. I could hear the fan running ,and then it sounded like it kicked into a higher gear ,and the temp gauge was getting higher( before the gauge hadn't really moved) I turned it off. Could all of this be from a bad heater core ? Is there anything else I should check first ?

Thank you ! Tom
 

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Is the windshield slimy? Remove the front passenger floor mat, is the carpet wet with coolant?

Clint
 

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1. You need to diagnose the point of leakage. Clean off engine real well, rent a radiator pressure tester or have a shop use one to find the leak, and then fix it. Yes, it could be the heater core, but don't make such assumption yet.

2. Make sure ALL the air is bled out of the cooling system.
 
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Discussion Starter · #4 ·
Is the windshield slimy? Remove the front passenger floor mat, is the carpet wet with coolant?

Clint
The windshield was just fogging up on the drivers side. You can smell the coolant with the heat on. I don't feel anything wet in the floor.
 

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Discussion Starter · #5 ·
1. You need to diagnose the point of leakage. Clean off engine real well, rent a radiator pressure tester or have a shop use one to find the leak, and then fix it. Yes, it could be the heater core, but don't make such assumption yet.

2. Make sure ALL the air is bled out of the cooling system.
There is a strong smell of coolant with the heat on ,and fogging only the drivers side ? How can I get the air out without needing any special tools ? I have heard of parking on an incline ? I added almost another gallon this morning.
 

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Discussion Starter · #6 ·
Is the windshield slimy? Remove the front passenger floor mat, is the carpet wet with coolant?

Clint
I just checked the carpet ,and windshield. Nothing wet or slimy it seems.
 

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Just outside of the firewall under the hood is where the heater core connects to the heater hoses and there is a plastic connection which gets brittle with age. On my Pathfinder it fractured and started a small enough of a leak to smell it. Traditionally if the core is leaking it gets wet on the floor, maybe it’s a very small leak.

Clint
 

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Discussion Starter · #8 ·
Just outside of the firewall under the hood is where the heater core connects to the heater hoses and there is a plastic connection which gets brittle with age. On my Pathfinder it fractured and started a small enough of a leak to smell it. Traditionally if the core is leaking it gets wet on the floor, maybe it’s a very small leak.

Clint
I have found no moisture on the floor on either side. Is that piece replaceable without removing the core ,if in fact that is the issue ?
 

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Discussion Starter · #9 ·
Just outside of the firewall under the hood is where the heater core connects to the heater hoses and there is a plastic connection which gets brittle with age. On my Pathfinder it fractured and started a small enough of a leak to smell it. Traditionally if the core is leaking it gets wet on the floor, maybe it’s a very small leak.

Clint
I had to put almost a gallon in this morning ,but doubt that was all lost since yesterday. One of these pieces ? I don't see any indication of leaks ?
 

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I replaced the one on the right with the aluminum tube attached. Either feel under that plastic piece or look under with a small mirror to see if it has residual coolant crust under there. As stated above you can pressure the system to see where it leaks from.

Clint
 

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If the coolant is leaking out of the evaporator case drain on the lower side of the firewall, it's the heater core. If you are smelling it inside the cab and it's fogging the inside of the windshield, it's probably the heater core. The fog on the windshield will usually have an oily feel to it, as well, if it's coolant. Heater core replacement is a real pain; you have to remove the dash and then the HVAC unit will need to be removed and opened up to get to the core.
If the leak is from one of the heater lines mentioned, you should be able to feel under it (don't do it when it's hot!) and end up will coolant on them. Get the part from Nissan, if that's the cause. Also, if you want to look at the evaporator case drain, your best view will be by removing the passenger-front wheel and looking behind the plastic wheel liner.
 
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Discussion Starter · #12 · (Edited)
I replaced the one on the right with the aluminum tube attached. Either feel under that plastic piece or look under with a small mirror to see if it has residual coolant crust under there. As stated above you can pressure the system to see where it leaks from.

Clint
Pretty sure it's the heater core now. There's an overflow from the core box through the firewall. That's where the puddle came from on the ground ,and probably the reason nothing is wet inside.
 

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Discussion Starter · #13 ·
If the coolant is leaking out of the evaporator case drain on the lower side of the firewall, it's the heater core. If you are smelling it inside the cab and it's fogging the inside of the windshield, it's probably the heater core. The fog on the windshield will usually have an oily feel to it, as well, if it's coolant. Heater core replacement is a real pain; you have to remove the dash and then the HVAC unit will need to be removed and opened up to get to the core.
If the leak is from one of the heater lines mentioned, you should be able to feel under it (don't do it when it's hot!) and end up will coolant on them. Get the part from Nissan, if that's the cause. Also, if you want to look at the evaporator case drain, your best view will be by removing the passenger-front wheel and looking behind the plastic wheel liner.
Thank you. I found the overflow this morning. It's definitely the heater core.
 

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That’s a big job and when the hoses get removed from the core those plastic pieces can let go so be prepared.
Me being me, I’d trade it in which is why I’m in my 16 and not my 10 which was an all time favorite truck of mine. It was needing a clutch soon and the exhaust wasn’t likely going to survive being man handled for the event, then the abs started going wacky so I called it quits. Sadly I had just myself done axle bearings, seals, brakes, belts, coolant, shocks and struts so that was $1000 plus my time. Oh well ?
Hope it works out for you as least costly as possible.

Clint
 
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The heater on these trucks is real sensitive if the coolant level is low. And the collect way to do a top off if just a little low is to leave the cap on the radiator and only add coolant to the bottle. The bottle is a degas bottle that is designed to remove air from the cooling system. Removing the radiator cap puts air in the system. There is a vent line off the top of the radiator cap that goes to the bottle. And a line off the bottom of the bottle that feeds the engine. So as you drive the air in the engine and heater will pass through the vent line into the bottle and the engine will pull coolant in its place, so long as the bottle has enough coolant in it.

Another thing people get wrong is putting the caps on backwards. The radiator gets the cap with only a rubber gasket, the bottle gets the one with a spring. The bottle is part of the pressurized cooling system.

Now as far as the leak goes, smells travel. But you have a leak, that is for certain. Smell + low coolant confirms it. Location TBD.
 

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Discussion Starter · #16 · (Edited)
That’s a big job and when the hoses get removed from the core those plastic pieces can let go so be prepared.
Me being me, I’d trade it in which is why I’m in my 16 and not my 10 which was an all time favorite truck of mine. It was needing a clutch soon and the exhaust wasn’t likely going to survive being man handled for the event, then the abs started going wacky so I called it quits. Sadly I had just myself done axle bearings, seals, brakes, belts, coolant, shocks and struts so that was $1000 plus my time. Oh well ?
Hope it works out for you as least costly as possible.

Clint
I had thought about trading ,but I wanted to get my CCs paid off before I did that. Might just keep this one for a warm weather vehicle since it's paid for if I can bypass the heater ? I can't find what those plastic pieces are. I have a manual ,but can't seem to locate them ?

The heater on these trucks is real sensitive if the coolant level is low. And the collect way to do a top off if just a little low is to leave the cap on the radiator and only add coolant to the bottle. The bottle is a degas bottle that is designed to remove air from the cooling system. Removing the radiator cap puts air in the system. There is a vent line off the top of the radiator cap that goes to the bottle. And a line off the bottom of the bottle that feeds the engine. So as you drive the air in the engine and heater will pass through the vent line into the bottle and the engine will pull coolant in its place, so long as the bottle has enough coolant in it.

Another thing people get wrong is putting the caps on backwards. The radiator gets the cap with only a rubber gasket, the bottle gets the one with a spring. The bottle is part of the pressurized cooling system.

Now as far as the leak goes, smells travel. But you have a leak, that is for certain. Smell + low coolant confirms it. Location TBD.
The heater core is bad. It's leaking out the overflow on the firewall.
 

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If you just hook the hoses together you will bypass the heater core. Still best to repair it as you’ll need it at times to dry any condensation from the windshield.

Clint
 

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Discussion Starter · #18 · (Edited)
If you just hook the hoses together you will bypass the heater core. Still best to repair it as you’ll need it at times to dry any condensation from the windshield.

Clint
That's the plan. I just don't know what those two plastic parts are. I would order them if I knew.
 

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