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Discussion Starter · #1 ·
I replaced the radiator with denso model from rock auto. Bled the system. New oem radiator cap. Filled up the overflow between the min and max lines and when I drive the car for a while the overflow is over the max line. Is this normal? It’s been pretty hot out but I assume the radiator should still have fluid in it when I take the cap off? When I do take the cap off it sounds like it’s releasing a lot of pressure. Never any issues with overheating and always stays at the center part of the temp gauge. Doesn’t blow white smoke etc out the exhaust and doesn’t seem to be losing any fluid anywhere just likes to hang out in the overflow.

Is this normal?

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Discussion Starter · #2 ·
I started it up and watched the fluid with the rad cap off. There is fluid in the radiator its just below the fins. Didn’t know it would fluctuate that much?!
 

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Sounds like the system didn't get completely bled the first time. Top it off again and see what happens. If you have a siphon pump pull it out of the overflow.
 

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Discussion Starter · #4 ·
Yea I just let it run for 20+ minutes with the cap off. It still has very small bubbles come out intermittently and those don’t seem to stop. Might have to do with the rad cap being off tho.
 

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Keep burping it continually (not continuously -- there's a difference) like that, with the heater on high, until the burping subsides.
 

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Slightly off topic, but did you have trouble getting the 2 bolts started that hold the radiator fan to the bottom of the Denso radiator?
 

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With regard to pic #2 in post #1, something ain't right.......when the MOTOR IS COLD, coolant level should be at the very top of the rad (cap removed), up in the neck, core not visible. New radiator caps have been known to be bad. Is it the correct rad cap? Pressurized rad caps have 2 valves and 3 sealing surfaces......plenty of places to be bad. Both valves and all 3 sealing surfaces MUST function flawlessly. When the motor cools, coolant should be drawn from the recovery bottle back into the radiator. Again, radiator should be full to the very top, MOTOR COLD.

Sounds/looks like the rad cap is allowing hot coolant to exit the rad and flow to the recovery bottle......but the reverse is not happening, coolant flow from the recovery bottle back to the radiator is not happening (as the motor cools).
 

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Discussion Starter · #8 ·
Slightly off topic, but did you have trouble getting the 2 bolts started that hold the radiator fan to the bottom of the Denso radiator?
I have a lift so it’s not a huge deal to see why they aren’t threading but yes transfer those over first so you aren’t upside down and backwards trying to reach. The screws went right in through.
 

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Discussion Starter · #9 ·
With regard to pic #2 in post #1, something ain't right.......when the MOTOR IS COLD, coolant level should be at the very top of the rad, up in the neck, core not visible. New radiator caps have been known to be bad. Pressurized rad caps have 2 valves and 3 sealing surfaces......plenty of places to be bad. Both valves and all 3 sealing surfaces MUST function flawlessly. When the motor cools, coolant should be drawn from the recovery bottle back into the radiator. Again, radiator should be full to the very top, MOTOR COLD.
that was my understanding as well and how it looks on my other Honda v6 motor. Seems like too much pressure to me and makes a loud WOOSH sound. The previous radiator cap functioned the same way and so did the cap from the other car so it’s not a cap problem. Car never overheats though. Does have 240k on it.
 

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Never remove the rad cap when the motor is HOT. When the motor is cold, you should not hear anything when removing the rad cap.....no WOOSH, nothing. When the motor is cold, completely cooled, there's no pressure inside the cooling system....should be the same as outside air pressure.

You may need to do a cooling system pressure test. The rad cap tested as well.
 

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I have a lift so it’s not a huge deal to see why they aren’t threading but yes transfer those over first so you aren’t upside down and backwards trying to reach. The screws went right in through.
What year is your pilot? I replaced my 04 radiator yesterday with a Denso and couldn't thread the bottom 2 bolts onto the passenger side fan brackets. The screws are just a tiny bit too short to bite into the threads of the clips on the radiator. It's a common complaint on the Amazon reviews for the Denso radiator. Luckily I had some longer screws with the correct size/pitch, but were too long, so I cut them down to fit. The OEM screws are 16mm long, and I made mine 20mm and it worked great.
 

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The rad cap spring has nothing to do with coolant being returned to the radiator, from the recovery bottle, as the motor cools. The spring in the rad cap releases at approx. 16 psi to allow hot coolant and any air to escape from the radiator to the recovery bottle. The 16 psi in the radiator/motor is what raises the boiling point of the coolant to approx. 260F.
 

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^^^^That is an excellent diagram of a radiator cap anatomy. Thanks for posting. Clearly shows the 3 sealing surfaces an 2 valves.


 

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Yea I just let it run for 20+ minutes with the cap off. It still has very small bubbles come out intermittently and those don’t seem to stop. Might have to do with the rad cap being off tho.
Hopefully, the bubbles you see are just trapped air that has not yet bled out of the system. Top up the radiator when it is cold each morning, never open it up when it is hot. Keep the correct level in the overflow tank. During your daily drive, run the heater on full for a while, to make sure that its bled too. After a couple of days of this, when you open the cold rad cap in the morning, the coolant level should be right up to the top of the radiator. The coolant level in the tank should stabilize, and not go up dramatically during your drive.

If you still have an issue with no visible coolant when you check the rad, then you probably have a coolant leak somewhere. If you can't see the leak or smell it, it's probably a head gasket issue, and the coolant is going out of the tailpipe.
 

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This is the method I use to burp air out of the cooling system.
 
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Discussion Starter · #18 ·
I checked it today cold. The coolant overflow was below the minimum line and the radiator had way more fluid in it so that’s good. I filled up the coolant overflow tank and topped off the rad. I’ll keep an eye on it. No visible leaks anywhere. No white smoke anywhere at anytime out the exhaust. No oil in the antifreeze. I’m hoping it was just a lot of air taking up space.
 

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"I’ll keep an eye on it".

That's a great idea. Presuming all is ok with the cooling system, COLD coolant level in the radiator should eventually always be at the very top of the rad, up in the neck. After checking the rad when cold, check the coolant level in the bottle. If the bottle coolant level is below the MIN mark when the motor is cold, add coolant to the bottle.

Start raising those hoods once a week folks and have a look around.(y)
 
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