# 05 Path Coolant level/Radiator cap??



## poki99 (Sep 9, 2011)

Ole girl is at 158k miles. I was driving and noticing the a/c was not blowing cool air. I pulled over and the car was overheating with dashboard gauge showing hot. Coolant was leaking out. We refilled with coolant directly into radiator until it showed full. Drove home and all was well. Checked level the next day and while there was some coolant in reservoir tank (slightly above Min line), i could not visually see coolant in the radiator itself. There is no leaking that I can see visually. I have a couple specific questions hoping you gurus can clarify...

1- How do I properly refill the coolant? Do I need to add directly to radiator til full then add to reservoir to Max line (while engine is cool)? Wondering if by filling radiator only and not reservoir did this not fill up all levels properly?

2- I read that only the reservoir tank has a pressurized cap. When I look at both the reservoir and radiator cap, they are both spring/gasket types. Thinking that the radiator should only have a seal cap (not one with the spring). Could this cause overheating issues? Or would it only be an issue if the reservoir didn't have a pressurized cap? Wasn't sure if there was still a prob if both have pressurized caps.

Definitely taking this issue to my mechanic ASAP but hoping you can clarify these questions.


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## smj999smj (Jan 1, 2006)

There shouldn't be any spring on your radiator cap, only on the reservoir cap. The radiator cap is rated at 42 PSI, whereas the reservoir cap is rated at 16 PSI, so you see where there would be a problem if someone put a conventional radiator cap on that didn't belong on your radiator. The radiator cap is Nissan # 21430-1P107 and I would avoid the aftermarket caps, if possible. As far as adding coolant, I would remove the radiator cap with the the engine cold and top it off, reinstall the cap, and then add coolant to the reservoir to the MAX line. Run the engine until it's warmed up and then make sure you have hot air coming out of the vents when you turn on the heater. If not, park on a hill with the nose of the truck up, or jack up the front of the vehicle as much as safely possible, and run the engine at 2000-3000 RPM until hot air comes out of the vents. Once that happens, you can shut the engine off and lower it, if jacked up.


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## poki99 (Sep 9, 2011)

Great info as always! Thanks. 

Can you confirm if I would still use Nissan # 21430-1P107 for an aftermarket radiator? I had to replace the radiator a couple years back. Also, the reservoir cap shows as 16psi only so I will need to replace this as well. Can you provide the part for this replacement? Thanks again!!


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## smj999smj (Jan 1, 2006)

The coolant reservoir cap is supposed to be 16 PSI, as I mentioned in my previous post. So, there really shouldn't be any reason to change it unless it's defective or you just feel like it. The reservoir cap is Nissan # 21430-1P111. The aftermarket radiator "should" take the same radiator cap as the original radiator, but I have heard of some lower quality radiators have fitment issues with the factory cap. I've heard some people have been able to "make it fit" with a little tweaking of the factory cap.


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## rogoman (Dec 16, 2004)

poki99 said:


> Great info as always! Thanks.
> 
> Can you confirm if I would still use Nissan # 21430-1P107 for an aftermarket radiator? I had to replace the radiator a couple years back. Also, the reservoir cap shows as 16psi only so I will need to replace this as well. Can you provide the part for this replacement? Thanks again!!


There should be no problem using the OEM #21430-1P107 rad cap on an aftermarket radiator; the necks are made to conform to the OEM standard. I've installed many aftermarket radiators using an OEM cap; in fact it's preferred to use the OEM cap as they much more accurate as to the pressure release spec.

However there's a problem with the cap pressure stated in this thread. The standard cap release pressure spec as stated in the FSM is: 14 - 18 psi. Here's a picture of the FSM page:


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## smj999smj (Jan 1, 2006)

rogoman said:


> There should be no problem using the OEM #21430-1P107 rad cap on an aftermarket radiator; the necks are made to conform to the OEM standard. I've installed many aftermarket radiators using an OEM cap; in fact it's preferred to use the OEM cap as they much more accurate as to the pressure release spec.
> 
> However there's a problem with the cap pressure stated in this thread. The standard cap release pressure spec as stated in the FSM is: 14 - 18 psi. Here's a picture of the FSM page:


Rogo, the pressure relief specs for the radiator listed in the FSM are misleading because it is not the radiator cap the controls the pressure in the system, but the reservoir cap. The radiator cap has no spring in it, just the metal cap and a rubber seal. Nissan doesn't put a spec listing on the cap itself, but if you look up any aftermarket radiator cap (Stant, Gates, Motorad, for examples), you'll see the pressure spec of 42 psi listed and stamped on the cap. I would imagine at that pressure it would simply blow out the seal, because could you imagine having the coolant system pressure over 40 psi? Something's gonna blow!  Really, the only purpose for the cap is for adding coolant to the system during servicing. Look up the reservoir cap, and you'll see the listing of 16 psi, dead middle of that 14-18 psi range. The system is different than what was used in pre-2005 Nissan trucks and similar to that used in many European makes for years.


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## rogoman (Dec 16, 2004)

Thanks for the insight SMJ. The FSM certainly is misleading. I've run into other issues with other vehicles where the FSM wasn't quite accurate but I think this is major. Oh well, live and learn.


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## smj999smj (Jan 1, 2006)

I remember the first time I removed the radiator cap off of my '06 Pathy and was like, "What the heck?!" And in reality, it's kind of pointless to put 42 psi on the cap because there is still a vent line and overfill hose running from the radiator neck to the overflow bottle. The radiator cap just doesn't apply any pressure to the coolant because of its design; it simply lets the coolant flow directly to the overfill hose back to the reservoir where the reservoir cap maintains the system pressure. I will say I have a lot easier time getting air pockers out of these systems than the older style.


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## poki99 (Sep 9, 2011)

Follow-up question... I purchased OEM radiator and reservoir caps. This afternoon I went to check my coolant level and when I opened the radiator cap coolant squirted out even though my engine was cool. I quickly closed the radiator cap then went to check the reservoir. When I opened the reservoir, I heard the sound of released pressure. My levels were fine. Why would coolant be squirting out like that on a cold engine?

Before changing the caps, I didn't have this problem. The problem I did have was that my vehicle over heated. When coolant was refilled there didn't appear to be any leaks after daily checks of the levels. I did notice that the wrong radiator cap was installed, this is what promoted me to ask my original question.

Any insight you can provide is greatly appreciated. Thanks!!


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## smj999smj (Jan 1, 2006)

Even if the engine is cold, the system can still be pressurized, assuming the engine has been operated at some time prior to removal of the cap. You should always vent the system at the reservoir prior to removal of the radiator cap.


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## tivo532 (Sep 14, 2017)

For at least 2 years, I've only covered the coolant reservoir with shopping bag plastic and a rubber band. And then replaced it a year ago with prescription med pill cap. It fits OK and no issue so far. Cheers!


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