Coolant going from radiator into overflow

[Liv_Nav]

G'day
I have noticed coolant going from the radiator into the overflow bottle in my 2005 ZD30, tried replacing the radiator cap and nothing has changed also recently changed the thermostat and now have a working heater and temp gauge.
- Car has no loss of power
- Does not blow smoke
- Does not overheat
- Starts good, nil issues
- Runs very well in general
- Coolant doesn't foam or seem to bubble in overflow
The only issue is the coolant going from the radiator into the overflow.
I have read that it could be possible head gasket or cracked head, with how well it is running I'm not convinced on it being a cracked head.
Any ideas?

Cheers

 

[Old.Tony]

First question is: does the coolant flow back to the engine as it cools down? How's the coolant level in the overflow on the next morning?

 

[Liv_Nav]

First question is: does the coolant flow back to the engine as it cools down? How's the coolant level in the overflow on the next morning?

I'm not sure what you mean I'm not that mechanically savvy, but I know that the overflow bottle level doesn't change overnight (when the car hasn't been running for a period of time) from when I last checked the levels after the car has cooled down. This morning I took the coolant from the overflow and fed it back into the radiator and ran the car from cold, there was no bubbling from the coolant in the radiator at all, there is also no coolant in my oil and I can't see any wet patches.
I drove the car to and from work last night - 1.5 hours each way, and there were no other issues besides the not staying in the radiator, I still had coolant in my radiator but not as much as what I started with.
I hope what I am saying makes sense hahaha

 

[Old.Tony]

It mostly answers my question.

Under normal conditions, as the coolant heats up it expands and pressure forces it to move to the overflow. When the coolant in the radiator/engine cools again it contracts, creating a vacuum in the radiator/engine which sucks the coolant back in from the reservoir.

There are a couple of things that could interfere with that process. I'd check the radiator cap to make sure it's seating correctly (a mechanic might need to look).

The other possibility is that the overflow bottle has been set up incorrectly. It's supposed to feed in coolant from the bottom and the hose at the very top is supposed to be freely open to the air (it's the actual overflow). If the hose from the radiator tank is connected to the top of the coolant bottle, it will happily fill the coolant bottle but when it starts to cool it won't be able to get coolant - it will be sucking air, the end result being a warm engine sending coolant to the bottle but not able to get it back. Make sure the coolant line from the radiator is connected to the BOTTOM of the reservoir.

 

[Erick]

I had similar problem and traced it to a very small hole that a rat had chewed in the hose connecting the radiator to coolant bottle. So check that hose holds vacuum

 

[Liv_Nav]

UPDATE: A mechanic recommended a sealwell cube so I added that in last night as directed but this morning on my way to work coolant flowed into the over flow bottle and actually overflowed wetting my wheel guard and side step. Again, car ran perfectly fine... I will have to take the over flow bottle off and manually feed it back into the radiator before making my journey home.
@Old.Tony I checked the overflow bottle and the hose is attached from the bottom, I think it is the original as it looks pretty old, I'm thinking of replacing it. The bloke who owned it before me had the radiator replaced and I reckon he did it for this reason, also he said the car wasn't driven all that much!
I also want to add that the car has only done 159,000kms!!
Thanks guys

 

[Navara Dave]

Not sure quite what you mean by overflow. The system had an expansion tank to allow the movement of coolant when it gets hot and expands. Are you sure that this is not part of the normal displacement of hot water within the pressurised system.

 

[Liv_Nav]

Not sure quite what you mean by overflow. The system had an expansion tank to allow the movement of coolant when it gets hot and expands. Are you sure that this is not part of the normal displacement of hot water within the pressurised system.

As in that when the car is running coolant would move from the radiator into the overflow bottle until it is full and then flow out of the overflow bottle outside of the car, good by coolant.

 

[Old.Tony]

I understand that the issue is this: coolant flows from the radiator to the reservoir while the engine is running but it doesn't flow back when the engine cools. A subsequent running of the engine could pump even more coolant into the reservoir causing the reservoir to overflow (causing a loss of coolant) and still the engine doesn't draw the coolant back.

If that's correct, it's also possible that the engine's coolant galleys aren't perfectly sealed. Perhaps around the turbo (which has coolant flowing through it) or even the heater matrix inside the cabin - if there's a tiny leak in any of the coolant system it could suck air into the engine rather than drawing the coolant back (a fluid system will always find the path of least resistance).

Time for a pressure test of the radiator, I think.

 

[dagotstering]

From the above I assume your radiator cap of the overflow tank is damaged. Please check and replace it . It’s a pressure release type. The actual radiator has Normal cap without spring. don’t swap them.

 

[Horatius]

G'day
I have noticed coolant going from the radiator into the overflow bottle in my 2005 ZD30, tried replacing the radiator cap and nothing has changed also recently changed the thermostat and now have a working heater and temp gauge.
- Car has no loss of power
- Does not blow smoke
- Does not overheat
- Starts good, nil issues
- Runs very well in general
- Coolant doesn't foam or seem to bubble in overflow
The only issue is the coolant going from the radiator into the overflow.
I have read that it could be possible head gasket or cracked head, with how well it is running I'm not convinced on it being a cracked head.
Any ideas?

Cheers

I don't get around here much anymore since the old nav passed on, but thought I'd respond to this.

The head cracked on mine and I didn't think it worth repairing. A small hose to the egt valve split with Mrs H along the freeway. So just to make sure the head cracked she let it cool for a while, then drove it another 10kms (minus coolant) to an exit and somewhere safer to stop lol (certainly don't hold that against her though, and in fairness the damage was already done by then).

It had the exact same symptoms as yours (also a zd30). There was absolutely no difference in the way it ran. Started first kick, no overheating, no loss of power, no smoke, still sounded great. So this doesn't necessarily mean you don't have a cracked head (have never heard of one of these doing a head gasket).

I thought about keeping it just for the wife to run around town as it didn't lose coolant on short <20km trips. On longer trips where it heated up properly it lost coolant out of the overflow though.

It doesn't take much of a crack between a cylinder and the water jacket to pressurise the system and force water out this way. A radiator place should be able to pressure test the system. Though it wouldn't surprise me if it was ok, but that doesn't mean it's ok at the temps you'll reach flying along the freeway.

I had a different make diesel that I drove around for years with a cracked head. From a restricted radiator. The temp gauge started going up one day on they hwy, slowed down and temps dropped didn't boil or anything. That was enough to crack the head. Made no difference to the way it ran and it rarely gave me a problem. Occasionally (could drive it for many months at a time with no problems) it would overheat, out of the blue. Let it cool, top up the coolant and would be fine again for months. When I took the head off it was cracked. So they can do funny things with a cracked head.

I agree the previous owner replaced the radiator for a reason (overheating) and this doesn't sound encouraging. A cracked head would be a common result of a restricted radiator. It really doesn't take much overheating to achieve this on the little 4 cyl diesels they put in dual cab utes.

Unfortunately there is no easy way (that I know of) to be certain that's the problem. It's a matter of checking everything else first and you might be lucky, but if everything else is ok...

Best of luck with it anyway.