After replacing Pressure cap and the top radiator hose assembly including the lower heater pipe hose and connector and checking the top heater pipe connector, I still have a coolant loss. On a 330 mile drive yesterday the car was great with no messages or codes, but when I checked the coolant this morning, although there was still residual pressure in the expansion tank when I loosened the cap, there was coolant in the front tank seam and drops on the right side of the tank like coolant had been blown back there and it was a cup low. I didn't see any coolant at the top radiator hose or the heater pipe connectors.

I'm not sure where to look next. Maybe a sniffer to see if the system is being over pressurized by a head leak? Can the expansion tank leak at a seam and still hold pressure all night?

 

The nipple where that small-diameter hose fits at the top of the header tank tends to crack until it eventually falls off, but well before that the coolant loss is noticed. Remove the hose and check it out. It is quite a common problem unfortunately.

 

In the second picture, where the small bleeder hose goes in, as Fraser said this is a very common ( if not the most ) place to leak. However, where the plastic bleed screw is just above this, there is an o-ring on it, have seen these leak ( o-ring). I have also seen the bleed screw leak itself as well. However I have never seen the "seam" leak on one yet, but doesn't mean it couldn't happen.

 

Check around the engine bay using a torch in the dark

You should be able to track down the dried residue from the leak
If you still cant find it add some ac die to the coolant this will show up with a black light

The 4 most likely places are
1. Expansion tank nipple
2. Expansion tank bleed screw
3. Elbow in the hose from the thermostat to the aux pump. Look at the inside of 90deg bend near the fan
4. Oring on the aux coolant pump body

Cheers
34by151

 

Thanks for the replies, Guys,

I had the pressure tank off when I recently replaced the top radiator hose and the nipple looked and felt OK. I’ll check the bleed screw O ring again, although it does hold residual pressure. I do have dye in the coolant so I’ll check the lower hoses in the dark again too. The flow of drops looked like they blew across the small hose rather than from it, so I’ll pull the cover and check under there again too.

Has anyone had the radiator leak at the top under operating pressure but still hold residual pressure? The drops looked like they might have come from under the cover or from the tank seam

Previously I’ve had all three coolant pumps out to replace the mechanical one, replace brushes in the aux pump, and discover that the SC pump was OK but the ECM was not grounding its relay coil to make it run. I replaced the thermostat at the same time and had 3600 leak free miles after that batch of work.

Then I replaced the pressure cap when coolant was being blown out around it and right after that I replaced the top radiator hose when a big leak developed at the lower heater pipe connector which is part of the top rad hose assembly.

I am still wondering if I have a high pressure situation in the system causing these leaks, but there was no coolant around the pressure cap like before unless air flow removed it and just let what accumulated at the tank seam blow over the end..

 

Drop by or call the local AutoZone and ask if you can use a radiator pressure tester. Pump it up to around 15psi and look for your leak.

 

I previously pressure tested at a T between the hose and the nipple at the expansion tank. I assumed this would pressurize the radiator too. Reasonable assumption or not?

 

That's one way to do it I guess. Good luck on finding your issue.

 

I had a similar situation a while back and decided it was the seam. Cleaned it with alcohol and put a bead of High Temp silicone around the tank, no more coolant on the tank lip. Been several months now.

 

I don't want to sound like the Voice of Doom, but there should not be any pressure in the cooling system when it is cold. If there is, it indicates possible HGF with combustion chamber gases pressurising the coolant jacket. Shops usually have an electronic gizmo that checks coolant for combustion chamber gases and other products.

 

Fraser, you always check the cooling system when it's cold when you pressure test it.

 

Agreed. After sitting overnight mine still has residual pressure and it has been like that for some time (both before and after after several leak "fixes", but not so much during).

I asked my British car club list if anyone has a sniffer. No replies yet. If not I'll try a $30 one from eBay - could be useful for the rest of the fleet too.

If I have a head gasket leak it does not seem to affect performance - perhaps a hot engine leak but not a cold engine leak? The oil looks clear. Most problems I've had (besides engine and tranny mounts) have been coolant, electrics, or battery related.

 

A pressure test done with a cold engine will not show up leaks that occur when hot.
A case in point was my aux coolant pump. The O ring on the body would only leak when hot. The expansion came from the heat rather than the pressure.

As I posted the leak was found using die and an led uv torch. Once I located the residue I tracked down the exact source using my inspection camera

Cheers
34by151