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Just bought my 2nd 1997 XK8 Convertible and am going through it seeing what needs to be done. I took the coolant tank cap off and found this orange goo underneath. I know it can't be good since it's probably in the radiator as well, but I hope it's not a result of a head gasket leak.
Most likely at some point coolant was added that was not compatible with the existing coolant. There are a few threads warning against mixing coolant types causing the goo mess. You are going to have to drain, flush, drain, flush to get rid of the mess. It will flush out but don't forget to have the heater running to get it out of the heater coil. I would start with draining it and adding water only and get it up to temp, let it cool and drain again. Do it as many times as it take to get it clean. You might also want to remove the wheel arch liner and remove and washout the recovery bottle.
Yes its a common fault. Personally id remove the filler cap. A bottom hose. Then stick a hose pipe and flush it through. You will be lucky if the heater is not messed up to. Not to mention the thermostat. It will take some doing to clean up your system. Once you think you have most of it out you will have to use a good radiator flush. Bring it up to temp to open the thermostat and put the heater on to ensure the entire system is clean. Another good flush through. Empty and fill with the right coolant.
....and this is not head gasket leak. The result of such a leak would be a voluminous froth like beaten egg.
Is the goo being created - in other words, have you cleaned the cap and more goo is generated? It is worth checking whether there is a current problem, or whether it is merely a left-over from a previous (and perhaps now resolved) event.
If this is in fact confirmed to be the result of gelling, I would do a thorough cleaning, and open the system in 2 different spots: thermostat and heater core (2 hoses by the firewall). Then I would power flush (garden hose) these separate sections. Flush and back flush. The heater valve defaults open, so pushing water through the heater hoses, through the octopus hose and off the thermostat area should not be a problem. Radiator would have to be actively flushed, too. Double check if you have an EGR valve as it is also water-cooled with small diameter hoses. Once free of this goop, then put everything together and do a standard cleaner. I would defer to someone more experienced in the engine cooling passages to confirm this is good enough for the engine block itself (not sure how small the smallest passage is). The obvious problem is that these cars do not have a lot of residual value, and the consequences of overheating can be quickly very expensive. Better to "over-clean", so to speak.
Other thing is to keep some of that goop around so you can test if radiator cleaner (or anything else) can somehow dissolve it "on the bench", and how long it takes. Just a thought.
If this is in fact confirmed to be the result of gelling, I would do a thorough cleaning, and open the system in 2 different spots: thermostat and heater core (2 hoses by the firewall). Then I would power flush (garden hose) these separate sections. Flush and back flush. The heater valve defaults open, so pushing water through the heater hoses, through the octopus hose and off the thermostat area should not be a problem. Radiator would have to be actively flushed, too. Double check if you have an EGR valve as it is also water-cooled with small diameter hoses. Once free of this goop, then put everything together and do a standard cleaner. I would defer to someone more experienced in the engine cooling passages to confirm this is good enough for the engine block itself (not sure how small the smallest passage is). The obvious problem is that these cars do not have a lot of residual value, and the consequences of overheating can be quickly very expensive. Better to "over-clean", so to speak.
Other thing is to keep some of that goop around so you can test if radiator cleaner (or anything else) can somehow dissolve it "on the bench", and how long it takes. Just a thought.
Best of luck, keep us posted.
This sounds familiar............... a case of great minds think alike?
A simple test to rule out a more serious issue would be to drain half a gallon of the coolant into a transparent pitcher or similar container and allow it to decant for an hour or so. This will help rule out a rare but possible issue such as transmission oil in the coolant due to internal radiator failure, or worst case, head gasket failure. If you don't see any oil floating on top of the coolant, then your issue probably is just adverse interaction of incompatible coolants, and you've already received great advice on how to deal with that.
BTW, I've had excellent results cleaning heater cores with CLR (Calcium, Lime, Rust), available in kitchen sections of home stores, Walmart, etc. It's not recommended for use on brass or aluminum, so I limit soak times to about 30 minutes. Use at your own risk.
Help identify mystery goo
