Coolant Boiling In Top Radiator Hose

[dorifticon]

OK having some problems with the cooling system and this is very frustrating because

a) I spent a bunch of money on the motor and can't afford to cook it and

b) I feel like I've put a lot of effort into keeping the thing cool, but it's not working.

Basically, the car starts and drives as normal, the temp comes up slowly and the needle sits in the middle of the gauge at a 45 deg angle and stays there.

With the car parked and running, nothing seems untoward with the possible exception of the top radiator hose being quite soft (ie like it's not taken pressure?).

HOWEVER, about 20-30 seconds AFTER the engine is shut down, I can hear a bubbling/gurgling sound coming from the top of the motor. If I hold the top hose, I can feel the coolant boiling as if it was an electric kettle.

Clearly it's a concern that the coolant is getting to boiling point.

Also of concern is that I was only cruising around, not strapping it out or anything, and it's already pretty cold in Canberra, so god knows what would happen in the summer.

Other info:

-radiator is a 40mm cooling pro alloy radiator, purchased and installed new a couple of years ago

-factory overflow bottle/expansion tank is installed and appears to be working properly

-when the car is cold, the radiator is full to the brim.

-factory engine fan is in place and appears to be working at idle. However, the fan shroud is NOT installed.

-water pump is a new item, put in with new engine - less than 5000kms use.

-it's an RB26/30 hybrid motor.

-there was a leak in the top heater hose, going into the firewall on the passenger side, and it was losing coolant slowly from here but I re-tightened the hose clamp and it seems to be ok.

I have had a search in the faq but that seems to deal more with losses from the overflow bottle. The only other thing I can think of is, being an rb30 block, in net terms the cylinder head is sitting about 28mm higher in the engine bay than it otherwise would be - could this cause issues with bleeding or air bubbles in the system>?

Any advice greatly appreciated. THis is really concerning me.

Andrew

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Edited April 12, 2011 by dorifticon

[blind_elk]

Probably not a good idea to leave out the fan shroud. But I don't believe that is causing this "problem". I say "problem", because I think what is happening is perfectly explainable, and normal.

The situation of having the cooling system under pressure during engine operation is to increase the boiling point of the water. (coolant generally is added for metal protection, and ethylene glycol in the coolant lowers the freezing point of the water).

Obviously, when the engine stops, the pressure in the cooling system is removed. As the pressure reduces, it gets to a point where the pressure is less than that required to prevent the coolant boiling at its current temperature / pressure condition.

If you are not losing coolant, and the engine appears to be running at a reasonable operating temperature, then I don't believe there is anything to worry about. But, for peace of mind, might I suggest you get an external temperature gauge connected to monitor the actual coolant temperatures.

Edited April 12, 2011 by blind_elk

[dorifticon]

well, sure the pressure eventually drops, but bear in mind it doesn't seem to be pressurising even with the engine running and at operating temp. Also, most cars I have had/worked on hold pressure in the top hose until it cools down.

One of my mates suggested that the lower seal on the radiator cap - the one for the purge/overflow bottle - may be stuffed and instead of holding pressure, the system is just purging into the overflow tank. So one cheap test/fix will be to put a new cap on the radiator to see if that changes things. I'll post up any results I get.

PS re the fan shroud, I did what I could to refit it, but it just wouldn't go. with the big 40mm rad, it moves the shroud backwards to the point that the fan blades foul on it (even though Just Jap claimed it worked with the fan shroud...oh well)

[DVS JEZ]

try bleeding the cooling system again. Run the engine with the radiator cap off from a cold start. See if any air bubbles come out. But do it with the front of the car jacked up so the radiator is higher than the top of head

[R.3.2.G.T.R]

try bleeding the cooling system again. Run the engine with the radiator cap off from a cold start. See if any air bubbles come out. But do it with the front of the car jacked up so the radiator is higher than the top of head

or stick a coke bottle with the bottom cut off and electrical tape wrapped around where the cap would be.. bleed with the heater on full blast

[turael]

use the bleed screw as well. might be airlocked and not actually flowing - you can actually see water flowing across the top of the rad if you open the rad cap.

you have a temp sensor? put it in the top hose. easiest way to see if coolant is flowing. if it isnt, the temp sensor won't read anything because it won't have coolant to read.

does the top hose get hot? you shouldnt be able to touch it if it has boiling coolant in it. if its only "warm" then it sounds like coolant isnt flowing down it, maybe blocked thermostat or not bled properly.

so hows the thermostat?

here is what I would do:

- open bleed screw, does air or coolant come out?

- close bleed screw once purged and coolant is coming out

- start car with rad cap off, let it warm up and take it to around 4000 - 5000 rpm to kick start the coolant flow. if it's airlocked, this can break it - done it before.

- does water come out of the rad cap, or is it flowing across the rad? water coming out = blockage somewhere

- if it's flowing, is the coolant getting hot? stick yo finger in. should be hot!

- turn off, wait 10-20 minutes to let it cool a bit, then crack the bleed screw again (you will have to undo it almost the whole way and wiggle it to see if stuff is coming out)

- if still getting air coming out of the bleed screw, repeat this process of starting, revving, bleeding

the coolant should not really be boiling at any stage, especially under normal conditions in autumn.

as regards to pressure and heat, the system will be hottest right after shutting down, as the active cooling stops (fan and flow). this will also increase the pressure in the whole system. if you have coolant leaks "sometimes" it will most likely be right after turning the car off. after a few minutes the heat dissipates.

[dorifticon]

OK dumb question - where/what is the bleed screw?

[turael]

http://i161.photobucket.com/albums/t228/MrPs_skyline/Old%20car/Bleeder.jpg

circled in red - 10mm bolt - will probably be pretty seized up, once you crack it it should be fine though. don't lose the washer.

[Mayuri Krab]

- does water come out of the rad cap, or is it flowing across the rad? water coming out = blockage somewhere

With regards to this, I thought coolant would flow out from the radiator neck (cap off) when the engine is cold as the thermostat would be closed at this point, therefore blocking/restricting coolant circulation?

And once the engine is up at operating temperature (thermostat open and hence no longer blocking/restricting coolant circulation), and hence coolant will no longer flow out & just flow normally through the radiator?

At least that what I'm seeing with my car atm; my coolant keep on flowing out if I start it with no rad cap on, however once engine is at operating temperature coolant would no longer flow out & just flow normally in the rad tanks.

Or is my understanding completely wrong?

I'm pretty noob with these things...

Edited April 12, 2011 by Mayuri Krab

[dorifticon]

I had a look at the rad cap that was on there, visually it appeared ok but I did notice that not much force was required to push it down onto the mating surface before twisting the cap.

I put in the Nissan oem one and the top hose seems to have firmed up and no more boiling coolant in the top hose on shutdown.

Interestingly the Nissan oem one is 0.9 bar and the just jap one is 1.1 bar. So the just jap one must have been really stuffed.

[dorifticon]

http://i161.photobuc...car/Bleeder.jpg

circled in red - 10mm bolt - will probably be pretty seized up, once you crack it it should be fine though. don't lose the washer.

Anyone know whereabouts it is on an RB26? Same kind of spot?

Maybe I could use the water temp sensor as a bleed point.

[R.3.2.G.T.R]

on the left hand side, near front of your fuel rail

[turael]

With regards to this, I thought coolant would flow out from the radiator neck (cap off) when the engine is cold as the thermostat would be closed at this point, therefore blocking/restricting coolant circulation?

And once the engine is up at operating temperature (thermostat open and hence no longer blocking/restricting coolant circulation), and hence coolant will no longer flow out & just flow normally through the radiator?

At least that what I'm seeing with my car atm; my coolant keep on flowing out if I start it with no rad cap on, however once engine is at operating temperature coolant would no longer flow out & just flow normally in the rad tanks.

Or is my understanding completely wrong?

I'm pretty noob with these things...

It's my understanding that the pump pushes water out of the hose with the thermostat in it - so when it's closed there is no flow. If there's a blockage and you take the cap off you can really notice it cause it pours out quite a bit. not sure why yours would be gushing coolant while cold...

[gotRICE?]

use the bleed screw as well. might be airlocked and not actually flowing - you can actually see water flowing across the top of the rad if you open the rad cap.

Thats somethig i have never seen before.. This, and the hoses are both on the same side of the Rad!

Mine just sits there and the water bobs up and down.

This of course is assuming the radiator is the same style as the stock one.

[Tony de Wonderful]

Obviously, when the engine stops, the pressure in the cooling system is removed. As the pressure reduces, it gets to a point where the pressure is less than that required to prevent the coolant boiling at its current temperature / pressure condition.

Well the system looses any dynamic pressure but it's still experiencing the static pressure caused by the radiator cap.

But your idea sounds good and it would suggest that the system is running very hot indeed if it is able to boil despite the rad cap.

[Tony de Wonderful]

Obviously, when the engine stops, the pressure in the cooling system is removed. As the pressure reduces, it gets to a point where the pressure is less than that required to prevent the coolant boiling at its current temperature / pressure condition.

Well the system looses any dynamic pressure but it's still experiencing the static pressure caused by the radiator cap.

But your idea sounds good and it would suggest that the system is running very hot indeed if it is able to boil despite the rad cap.

[Mayuri Krab]

Thats somethig i have never seen before.. This, and the hoses are both on the same side of the Rad!

Mine just sits there and the water bobs up and down.

This of course is assuming the radiator is the same style as the stock one.

This is what I see with mine as well, after the engine has warmed up; coolant just pluses slightly up & down around the rad neck area...

Also after my lastest fix of the "never ending cooling system quriks" for my car I just noticed that my 2 hoses are pretty soft even when the car is at operating temperature (aftermarket gauge reads ~80 deg C) & after turning it off.

No signs of overheating/boiling coolant though, so I guess its down to Nissan tommorrow for a proper OEM cap, as the current cap I've got is some generic 13psi one from SCA.

[turael]

Thats somethig i have never seen before.. This, and the hoses are both on the same side of the Rad!

Mine just sits there and the water bobs up and down.

This of course is assuming the radiator is the same style as the stock one.

*shrug*

I don't actually know but I'd be surprised if the rad was letting the flow go straight down the end tank Wouldn't it be blocked off on the side?

I can't say this happens for all cars, I just know it happened in my case:

- coolant top hose was full of air, rad cold, engine hot, looking into rad was static water and a bit of it was coming out

- after bleeding properly and giving it a jab of throttle the coolant started moving, could physically see it flowing across the top of the rad

My setup is a bit different to most though. Radiator is mounted behind the seats and has something like 6m of hoses to get there. I can see anyone reading this scratching their heads, so here:

pic1, rad at back, can see pipes going straight down

pic2, pipes in trans tunnel, pipes go under engine and then up

I've had to modify the idle a little or it will stall fairly often, I think this is simply because of the effort the pump has to go to to pump the distance. New pump, new belt. Planned upgrade to include an electric pump in the system at the rear to assist.

[gotRICE?]

*shrug*

I don't actually know but I'd be surprised if the rad was letting the flow go straight down the end tank Wouldn't it be blocked off on the side?

I can't say this happens for all cars, I just know it happened in my case:

- coolant top hose was full of air, rad cold, engine hot, looking into rad was static water and a bit of it was coming out

- after bleeding properly and giving it a jab of throttle the coolant started moving, could physically see it flowing across the top of the rad

My setup is a bit different to most though. Radiator is mounted behind the seats and has something like 6m of hoses to get there. I can see anyone reading this scratching their heads, so here:

pic1, rad at back, can see pipes going straight down

pic2, pipes in trans tunnel, pipes go under engine and then up

I've had to modify the idle a little or it will stall fairly often, I think this is simply because of the effort the pump has to go to to pump the distance. New pump, new belt. Planned upgrade to include an electric pump in the system at the rear to assist.

LOL! Thats awesome! But yes a very diff setup

No car i have ever owned has had visible flowing water. It doesnt mean it doesnt do it, but im guessing because the level is up inside the cap neck area you dont see it. Maybe if the water was low enough to see the tops of the core then the flow would be visible?