Losing Coolant 1990 5.0 Gt


Sep 4, 2010
I am having to re-fill my coolant reservoir about every month or so. I have had the system pressurized - no apparent leaks. Replace the water pump and flushed the system. The reservoir cap does not fit well - could I be losing coolant through evaporation? BTW no water in the oil
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Drive the car up to autozone and rent or borrow the tool to pressure test the system it has the attachment for the cap. The cap should hold 16psi. The system pressure check is a higher psi than that. The kit has the pressure setting for the system. Retest them both
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If you are losing coolant it could be a number of things- a small leak in a hose, water pump, intake, thermostat, head gasket, bad cap, cracked overflow tank. I know you said you pressure tested the system but did you do it correctly? You need to bring it up to 16lb and let it sit for some time. IMO if you had a bad cap, you would be seeing higher temps and visually coolant marks on the radiator neck or side from the overflow.

Also, you don't need to have water in the oil for a HG to be blown or leaking. You could have a hole or small tear around a water jacket and the coolant is getting burned off. Do you see any white smoke under acceleration or when idling. The best way to check is to rent from Autzone an exhaust gas detector and dye. The dye is blue in color and vacuum will pull the gas from the top of the radiator through the dye and up the tube. Pray to the auto God that the dye does not turn color to a green. That means you have exhaust gas in your coolant and a sure sign a HG is gone.

I was loosing coolant, and it turned out to be a simple fix. I thought all the clamps were tight enough, but under pressure it leaked a little on the firewall and evaporated before you could see it drip. One of the hundred hoses on my SHO had a pin hole under pressure. I think some dye is a good idea.
Had same issue with mine..it was the head gasket...got another engine, low mileage..same issue...was missing a head bolt, the head of the bolt was gone...lol...get good copper gaskets...and get a quality valve job, car will drive like new.