Odd radiator behaviour!!

[Kennedy]

Hoping to get some advice on a confusing issue with my radiator -

I recently put a new aluminium/3 core/75mm thick radiator in my 1999 TD42 turbo ute and now have the following symptoms -

1. coolant pushes into the overflow bottle as it heats up as per normal however it doesn't suck it back in when it cools
2. After a run and parked in shed overnight so its properly cooled - cracking the radiator cap results in a significant amount of pressure being released through overflow bottle
3. Even when I ran it with cap off until temp gauge about 1/4, turned off and put cap on, next morning there was still pressure released when cracking cap and no draw down in overflow bottle level and radiator coolant level still full

I have checked line to and non return valve in overflow bottle and same results with thermostat in or out.
There are no bubbles in coolant when running and no evidence of water in oil or exhaust.
I put the original cap on with no change.

I spoke to a radiator 'guru' who suggested there might be a combustion leak which only happens when the motor is under load and that I should get it on a dyna tune so they can check for bubbles while under load.
I thought this made sense however after doing the test as per 3 above I am not so sure.

'When I was a boy"....the only trouble you had with radiators was when a stick poked a hole in them!!

[Turtle_au]

The radiator cap has 2 seals. At the bottom is the pressure seal for the cooling system with the spring . Under the top of the cap is another seal to keep air out and lets the system suck the overflow back in.
The neck on the new radiator may be a bit shorter making the spring push harder, or the seal under the top of the cap is missing which has the same effect.

Sent from my SM-T355Y using Tapatalk

[Kennedy]

The radiator cap has 2 seals. At the bottom is the pressure seal for the cooling system with the spring . Under the top of the cap is another seal to keep air out and lets the system suck the overflow back in.
The neck on the new radiator may be a bit shorter making the spring push harder, or the seal under the top of the cap is missing which has the same effect.

Sent from my SM-T355Y using Tapatalk

Checked all the dimensions - the cap that came with it is a 1.1 and the cap off my old radiator which I am now using is a 0.9, there is .5mm difference in their overall length(which I guess is the pressure rating differential?) Other than that everything looks OK....top and bottom seals look like they've been seating evenly, depth of filler neck(top seal face to bottom seal face) identical to old radiator, top & bottom seal seat faces look smooth and even.

I am thinking the solution lies in working out why the system retains so much pressure.

And here's an extra puzzle - See symptom 3 in my first post - I did that test, cracked cap this morning about 7.30 and put it back on fully. Went back 10 min ago to double check dimensions etc before replying - when I cracked the cap again there was some pressure released!!!! Its an overcast day today so I don't reckon ambient temp has risen by more than 5-7 degrees since 7.30am.

[Turtle_au]

Before you crack the cap, how firm is the top radiator hose? And after?
When you remove the cap, is the coolant level ok?

With engine cold and cap on, mark level in overflow.
Warm engine up to normal temp, switch off and check tank to see if level has changed. If it has remark level.
Let engine cooldown and check level again.


Sent from my SM-T355Y using Tapatalk

[Kennedy]

Before you crack the cap, how firm is the top radiator hose? And after?
When you remove the cap, is the coolant level ok?

With engine cold and cap on, mark level in overflow.
Warm engine up to normal temp, switch off and check tank to see if level has changed. If it has remark level.
Let engine cooldown and check level again.


Sent from my SM-T355Y using Tapatalk

As per symptom 3....coolant level still full. Will check radiator hose this evening as just came back from a run in it.

Marked level in overflow and took it for a 10k run...gave it heaps.... overflow level has risen 12mm.....will check level again this evening when it cools down.

I am still trying to get my head around the fact that when I opened cap yesterday and released pressure then opened it again 4 or 5 hours later there was pressure in tank again. I'm starting to think the radiator guru I talked to is on the right track though I am wondering that if there is a crack that's slowly releasing combustion pressure into cooling system and perhaps still releasing that pressure after shut down then it would be long odds that the motor stops every time with the same piston on compression stroke with both valves shut. Not sure how it works exactly but I imagine there might be 2 cylinders at that position at any one time....am happy to be enlightened on that assumption.
Given that assumption I'd reckon it might be leaking across head gasket ??

[dom14]

Reserve tank cap has a hose from the underside of it that goes into the bottom of the reserve tank.
If that hose is somehow disconnected, the coolant has no way of travelling back to the radiator as the radiator cools down.
The end result is the coolant loss by coolant gradually filling up the reserve tank and spilling out of the hole on the reserve tank cap.

[Kennedy]

It's attached dom

[Turtle_au]

If coolant flowing into overflow tank, radiator level stays full, then it looks like it's drawing it back into system.
If not overheating or other engine issues then I would just keep an eye on it.
Long shot, maybe it's just due to the radiator being aluminium, expands and contracts more.

Sent from my SM-T355Y using Tapatalk

[dom14]

It's attached dom

Put a new radiator cap and see how it goes. Cap should match with what's says on the service manual, the pressure rating wise.

Combustion gas leak is something you can DIY test with an ebay kit or as I did make your own with a CO detector/alarm.
You can also do a litmus test 'cos chances are the coolant PH level can go below 7(acidic) from the combustion gases mixing up with water.

Little bit of pressure coming out of the radiator when you open the radiator cap should be ok.
If it gushes bubbles as the engine's warming up, then it's likely the combustion gases get into the coolant via a cracked head
or stuffed head gasket.

[dom14]

It's attached dom

You can use a homemade simple gadget like in below thread to check if there is excess "burping" happening in the radiator.

http://www.nissanpatrol.com.au/forum...urp-a-radiator