Bleeding cooling system with radiator cap on?

[mclasser]

The factory service manual for my I35 says to leave the cap on and then race the engine several times to 2500 RPM with the heater set to all the way hot. The common procedure, though, is to leave the cap OFF so the air pockets in the system have a place to rise and exit from. Is there something special about Nissan cooling systems I'm missing?

 

[eljefino]

The air will still get out either way. The cap releases pressure whether it's air, water vapor, or antifreeze.

Maybe the procedure is so AF doesn't spill on the rad neck/ surge tank and stink up the car or for some other non- purely mechanical purpose.

 

[147_Grain]

Leaving the Radiator Cap on while draining coolant from the bottom of the radiator will likely suck additional fluid out of the reservoir and a maybe a little out of the block.

I don't worry about this and just drain the radiator with (cold fluid) each fall and refill with a gallon of fresh anti-freeze to rejuvenate the rest of the cooling system (cost is only $13.00 per year). This is performed with the engine off to minimize air bubbles. (Same principle is done with the ATF each spring with a simple drain and fill for a cost of only $15.00 - $18.00.)

 

[Jimzz]

You cabn do it that way but I woudl also jack the car up so the cap/bleed poitn is the higgest. You almsot have to do this in many GM 3.1 setups to bleed well.

 

[jaynissan12]

I don't know but I know the frontier's from 2005 on are a nightmare. You gotta replace the reservoir and radiator cap every 30K if you don't want air getting in the system. Started happening to mine shortly after 30K, started noticing it on take off with water rush noises and heater not functioning properly. They use the reservoir cap as the pressure relief in this set up. My understanding is the heater core is a bad setup on it and has a tendency to draw air from any weak point in the system. I still have a little air in mine at 44K after replacing the caps, tried bleeding it, squeezing hoses, but I am not going to pay a dealership to do it as long as its not affecting anything. BTW the reservoir went dry in mine, guess due to vapor release from the cap or the radiator was releasing it in very small amounts over time, just a guess on what happened with mine.

I did the bleeding with the cap off as it warmed up, they tell you to race the engine to 2500rpm to 3000rpm for 10 seconds and to place the cap on if it tries to overflow the neck. I did that 3 times, made a mess, it would also suck a lot from the reservoir while doing this and I still heard air in the heater core (I kept the core open all the way during this as it says). Best effect I have gotten so far was to do that, put the cap on, rev it, take the radiator cap off, air will come out, do that a few times, then take the cap off and leave it off. Squeeze the heater hoses and more air will come out while the cap is off. Doing this got rid of most of the air in my system. Undoubtedly this is a common problem with Nissan.

 

[OneEyeJack]

It's okay to follow the factory manual. Try it. It might just work.

When you think you're done, I'd repeat it once a week for a couple of weeks.

It's important to get out as much air as possible.

 

[Chris142]

I always put the cap on.prevents a mess

 

[Rand]

you can get one of those giant bleeder funnels.

 

[ARB1977]

Cap off with a few hits of the throttle is all it takes to burp the system. At least on my vehicles.

 

[razel]

Nothing special about the Nissan cooling system in our cars. I have the 01 I30. I always followed what I was taught prior which was cap off. I've drained/refilled 4 times and flushed once, no issues cap off. I'm sure there's no issues cap on either.

 

[SnowDrifter]

I use a spill free funnel kit and dump the leftovers in the overflow

 

[fdcg27]

Most systems will bleed themselves either way.
Our '86 Civics actually had a bleed valve on either the block or the head, can't remember which.
The Aerostar required special proceedures for bleeding, but seemed okay even though I ignored these.
Fill it up, drive it on a typical day's use and then top it off a time or two.
All that's really needed for any cooling system I've ever had the pleasure of knowing.

 

[Merkava_4]

If the reservoir is vented to atmospheric, there's no need to leave the radiator cap off.

 

[hotwheels]

Originally Posted By: mclasser
The factory service manual for my I35 says to leave the cap on and then race the engine several times to 2500 RPM with the heater set to all the way hot. The common procedure, though, is to leave the cap OFF so the air pockets in the system have a place to rise and exit from. Is there something special about Nissan cooling systems I'm missing?


To prevent the overflow reservoir from living up to its name, you may want to elevate the reservoir until the coolant system has expelled all air. Alternatively, you may be able to screw an overflow extension to the reservoir where the screw-lid goes. VW offers a screw-in adaptor that allows you to extend the overflow reservoir with a length of coolant hose. Maybe you can get something like that for your Nissan.

hotwheels

 

[The Critic]

You can install the cap loosely - that's what Honda has you do.

But I service a lot of these Nissan systems. I use an airlift to fill them, then use a coolant funnel to bleed. Keep the engine RPM at about 2500 and it will get to operating temperature fairly quickly. The heater needs to be left at the highest temperature setting but with the fan on the lowest setting.

Use a scan tool and watch for the thermostat operation. It needs to get up to temperature for the thermostat to open and close at least twice. A good indicator of this would be the cooling system fan.

You can certainly do all of this without the Airlift, but it makes the job a lot easier. Sometimes the thermostat does not open and you will need to turn off the car, and allow it to cool, and then start over.