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!! :p

[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.

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[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.

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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.


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[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.


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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.

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[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/forums/showthread.php?35523-How-to-burp-a-radiator

[Kennedy]

Thanks dom.....I get the same results from the cap supplied with new radiator as I do with cap from old radiator

I saw the post re combustion gas tester...might try the litmus test first

What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!

Checked overflow level this evening...it is still sitting at 12mm higher so doesn't seem to be sucking it back as it cools....BUT.....radiator is still full ????

[dom14]

Thanks dom.....I get the same results from the cap supplied with new radiator as I do with cap from old radiator

I saw the post re combustion gas tester...might try the litmus test first

What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!

Checked overflow level this evening...it is still sitting at 12mm higher so doesn't seem to be sucking it back as it cools....BUT.....radiator is still full ????

Yeah, the sucking back from overflow tank is not always perfect IMO, as it depends on the proper function of the radiator cap & outside temperature. Coolant system can develop tiny bit of cavitation inside the coolant passages due to water pump activity and uneven distribution of heat at the start up. Unless coolant blows out of cold radiator when you open the radiator cap, I don't think it's a critical issue. If you can confirm there's no combustion gas in that gas that blows out of the radiator, I probably wouldn't worry about it.
Also, definitely check the quality of the coolant, 'cos if the coolant is acidic for whatever the reason, it will most certainly produce gas inside the coolant passages by reacting with the metal. Some cavitation is ok IMO 'cos as you know, when the water boils there's always bubble forming out of water/coolant. It's the excess cavitation we need to worry about, 'cos that means either the head gasket/head is stuffed or coolant is bad.
Remember though, if you use the simple coke bottle gadget as I did to burp the coolant system or monitor excess cavitation/combustion gas leak, you need to plug the hose that goes from the radiator cap to the coolant overflow tank, otherwise coolant and air from the coolant system goes into the overflow tank and you won't be able to see whether there's anything wrong with it.

[Kennedy]

Thanks dom...I'll have a go at making the 'burper' when I get a chance and perhaps get it on a dyno next time I'm in the big smoke.

As I said earlier ...."What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!"

[dom14]

Thanks dom...I'll have a go at making the 'burper' when I get a chance and perhaps get it on a dyno next time I'm in the big smoke.

As I said earlier ...."What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!"

Yeah I can't explain that with a possible theory off the top of my head right now, but if you say it happens, then it needs some investigation.
I suspect some kinda coolant reaction with the metal inside the coolant galleries or it could simply be the air bubbles trapped deep inside the engine block gradually surfacing to the radiator top when it's cold. If there's no combustion gas in the coolant, I wouldn't worry about it.

I've seen some guys using a plain plastic bottle with the right size bottle neck shoved into the radiator cap hole to perfectly air tight it, without having to build the simple gadget as in my video. That might worth a try if you have few different size plastic bottles hanging around in the rubbish bins, etc.

[dom14]

Another thing you can check is to see whether you have any 90 degree joints(T joints) in the cooling system.
I've been told it's better to replace them with Y joints to reduce cavitation.

[dom14]

I've seen some guys using a plain plastic bottle with the right size bottle neck shoved into the radiator cap hole to perfectly air tight it, without having to build the simple gadget as in my video. That might worth a try if you have few different size plastic bottles hanging around in the rubbish bins, etc.

You can wrap the plastic bottle neck with stick tape or a piece of bicycle tube and then screw the bottle into the radiator cap hole.

[Kennedy]

Thanks dom, I will check it out

[Wizard52]

Do you have correct cap on overflow bottle as they are different.
When I installed new all alloy radiator, I did not notice the original cap was faulty in that rubber seal was folded under and did not seal. After noticing the fault, I swapped caps around and then coolant would not return from overflow bottle until I bought a new cap for radiator and returned overflow cap to correct place.
No problems since.
It is remarkable how the new radiator sucks the heat out and keeps temps down in recent 40+ temps even under load.

[threedogs]

Another thing you can check is to see whether you have any 90 degree joints(T joints) in the cooling system.
I've been told it's better to replace them with Y joints to reduce cavitation.

that is for gas systems mainly,