Tracking Down Coolant Leaks
Posted: Tue Jan 30, 2024 17:42
OK, in the last month or so I've had more practice at this than I would like, so I thought it would be worth sharing what I've been doing.
Undoubtedly the most useful bit of kit to help with this is a coolant pressure test kit. They can be picked up pretty cheaply from eBay, but you are welcome to borrow mine for the cost of postage - once I've fixed all my leaks!
I drained all the coolant out of the system when checking, on the basis that air escaping from a tiny hole is far easier to detect than water.
Pump the pump until you can hear some hissing somewhere, or until it's a couple of psi below the radiator cap pressure, whichever happens first.
It's not as easy as you might think to determine exactly where the hissing is coming from, but a bit of silicone tube stuck in your ear as a "stethoscope" really helps:
Once you have a suspect, a 50/50 mix of washing-up liquid and water can help to confirm. A small syringe with a short bit of hose is ideal to apply it to the suspect area, but in this case I just used a teaspoon:
See this video.
If you can pressurise the system and not hear any obvious hissing, still go around with the stethoscope and check all the ends of each coolant hose.
If you still don't find anything, leave the system pressurised for 5-10 minutes. If the pressure doesn't drop, you're good.
With my test kit, once above 10 psi or so it did have a tendency to leak at the tester cap, but a bit of wiggling usually managed to stop it.
If the pressure does still drop, then you must still have a leak somewhere you haven't identified. Obviously the heater matrix is hard to access and check, so don't go there until you've ruled everything else out (I went there too early and found it bone dry!). The only other option I can think of (please advise if there's anything else) is the head gasket, which is obviously more of a PITA to fix. But if there's a significant leak there, you'd expect other symptoms - either a white steamy exhaust (leak to the combustion chamber), mayonnaise in the oil system (leak between oil and coolant passages), or oil in the coolant (ditto).
Please do chime in with any useful experience, advice and/or tips anyone else has!
Undoubtedly the most useful bit of kit to help with this is a coolant pressure test kit. They can be picked up pretty cheaply from eBay, but you are welcome to borrow mine for the cost of postage - once I've fixed all my leaks!
I drained all the coolant out of the system when checking, on the basis that air escaping from a tiny hole is far easier to detect than water.
Pump the pump until you can hear some hissing somewhere, or until it's a couple of psi below the radiator cap pressure, whichever happens first.
It's not as easy as you might think to determine exactly where the hissing is coming from, but a bit of silicone tube stuck in your ear as a "stethoscope" really helps:
Once you have a suspect, a 50/50 mix of washing-up liquid and water can help to confirm. A small syringe with a short bit of hose is ideal to apply it to the suspect area, but in this case I just used a teaspoon:
See this video.
If you can pressurise the system and not hear any obvious hissing, still go around with the stethoscope and check all the ends of each coolant hose.
If you still don't find anything, leave the system pressurised for 5-10 minutes. If the pressure doesn't drop, you're good.
With my test kit, once above 10 psi or so it did have a tendency to leak at the tester cap, but a bit of wiggling usually managed to stop it.
If the pressure does still drop, then you must still have a leak somewhere you haven't identified. Obviously the heater matrix is hard to access and check, so don't go there until you've ruled everything else out (I went there too early and found it bone dry!). The only other option I can think of (please advise if there's anything else) is the head gasket, which is obviously more of a PITA to fix. But if there's a significant leak there, you'd expect other symptoms - either a white steamy exhaust (leak to the combustion chamber), mayonnaise in the oil system (leak between oil and coolant passages), or oil in the coolant (ditto).
Please do chime in with any useful experience, advice and/or tips anyone else has!