Good afternoon. Unfortunately life got away on me and I neglected to change/flush my coolant in my 1986 Mustang Gt 5.0 convertible. It is a 5spd. It was changed and flushed in 2014 with green fluid and since then it’s only been driven about 10000miles. I bought the car in 2011 with 48000miles and it now has 60000miles. A few years after the coolant was changed the heater core developed a leak and my mechanic at the time put in bars stop leak and that solved the issue. He also replaced the thermostat and pulled the radiator out and I think cleaned the outside of it.
There are no signs of coolant loss. The coolant does not look dirty. It is still green. You can see accumulations of gunk around the radiator cap and just inside the radiator but it’s not rust or oil Color. I did a ph test on it with an aquarium tester for fish and it was the top of the scale at 8.5. The actual PH May be higher but I have not tested it yet with an automotive test. I tested the coolant with a multimeter with the black lead to ground and red in the fluid. Engine not running it showed .20 initially and then fell to .10 in a couple minutes. Engine running indicated .33 initially falling to .15 in a couple minutes. I ran the engine and checked for leaks around the water pump and there is none. Nothing out of the weep hole. It looks like the lifter covers are leaking some oil. I does not use oil but I don’t drive it much. I always change the oil with full synthetic every spring with STP high mileage oil treatment the entire time I’ve owned it and that stopped the oil leaks.
I need to flush the cooling system and I’m wondering if I should install a heater core bypass so I can properly flush the cooling system first before changing the heater core. This way I won’t contaminate the new heater core with the flush and also possibly get fluid all over the passenger floor during a flush with the original damaged heater core? In this situation would the radiator/water pump, etc be damaged from not changing the coolant often enough? The car is 36 years old but most of the rad hoses seem to be in good condition.
Reading the foxbody mustang forums guys recommend getting the inlet/outlet of the new heater core reninforced as this is where cracks form and also getting the new core with a flow restrictor as apparently the pressure of the fluid can cause it to crack. Would you replace the thermostat and radiator cap with oem just to be sure as well? Hopefully I could just do the flush and heater core replacement and everything else is ok.
Most of all I’m concerned that I may have caused lasting damage due to corrosion, etc. Therefore would you recommend multiple low pressure flushes with distilled water and also uses a flush cleaner such as prestone total coolant flush? Is it worth replacing the coolant with a universal coolant that has a longer lifespan or just use the green fluid every year? My concern there a engine block drain plugs that can be hard to remove and there might me some green fluid left over and that’s bad for them to mix?
I watch your videos every day and also I’ve watched every video for the last five years or so lol. Your incredibly knowledgeable and I thank you for your help.
cheers,
Gareth in Calgary, Alberta, Canada
Just flush it out several times until the water runs clear. Don't worry about the core plugs.
Would you replace the thermostat and radiator cap with oem just to be sure as well
Yes. They're cheap enough.
Thank you. I appreciate your insight .
if you're not putting a lot of miles on i wouldn't worry that much. I have a 93 LX 5.0 that i purchased in 1998. I've changed the coolant a couple times , just drain and fill it up with new stuff. Hoses are all original. Rad cap and thermostat are cheap so replace those. I also changed the brake fluid and power steering fluid a couple times so maybe check that out as well, its easy to do.. One of the things i really like about this car is how easy it is to work on (unlike new models)
