A bad radiator cap - replace it with the correct one.

Also check the passage to the overflow to make sure it’s not clogged and inspect the neck as well. I had a pesky leak from the neck. There was a small chip on the lip where the cap seats.

The Stealth I bought for my daughter years ago had this problem which boiled down to a corroded thermostat housing where the radiator cap was supposed to seat. It was so chewed up it couldn't seal and just blew all the coolant out when it ran.

luv2rallye said:

A bad radiator cap - replace it with the correct one.

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Replace the cap and I now keep fluid in the reservoir. Thanks Luv2rallye for pegging this one right away!!!

Thanks everyone else for mentioning other things to check!

UPDATE: The cap didn't fix the issue. I took the GST our for a short run of 100+ MPH and the reservoir is empty. There is fluid all over the garage floor at retry. The overflow tube is dry, the radiator connections are dry, but I can't figure out where the massive leak is coming from. Any ideas where to check?

Every single DSMer needs a coolant pressure tester. Pressurize the system to 15psi and let it sit. If there aren’t any leaks it will hold. If it doesn’t get some soapy water and start spraying.

Jk's97DSM said:

Every single DSMer needs a coolant pressure tester. Pressurize the system to 15psi and let it sit. If there aren’t any leaks it will hold. If it doesn’t get some soapy water and start spraying.

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Any recommendations on a worthwhile kit? With my luck, I'd buy a kit that didn't have a converter for the DSM neck. Yes, I'm one of those guys.

Then replace all the hoses, therm, take the therm housing off and inspect and replace it w fresh rtv. Replace all your coolant hoses if they arent already brand new. Get the heater and tb hoses too! It can only be so many things. And its good maintenance too. I recently did all mine. Peace of mind.

That seems like a bad leak. Guessing it leaks when it’s pressurized. You should be able to find it with a pressure tester but I’m surprised you can’t see it. There aren’t too many places it can leak from. Start feeling around from the highest point.

Under the throttle body
Thermostat housing & neck
All the lines
Oil filter housing
Radiator
Turbo coolant lines

How old is the thermostat? Coolant would boil out of my reservoir at a stop after it’s been running in the highway on my jeep. It turned out my thermostat wasn’t opening all the way. The thermostat was 5 years old.

Jegs has a decent kit. Nothing in the system matters if it doesn’t hold pressure.

Don’t use RTV for coolant gaskets. Clean and flat surfaces with a decent gasket and the proper torque.

Jk's97DSM said:

Jegs has a decent kit. Nothing in the system matters if it doesn’t hold pressure.

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I agree and disagree. If the thermostat isn’t opening all the way, it will overflow out of the reservoir.

In general. The efficiency of the cooling system relies heavily on the system being able to maintain pressure.

UPDATE #2: After procuring a coolant pressure tester, there was a slit in the hose going to the turbo. Thanks JK for your tool advice!

just for reference which one did you get? I've had trouble finding one at the local stores. I haven't looked online

SAE 30R7 - this is the hose that goes under the intake into the turbo. Got it from an Irish-named parts store.

Hehe. I meant the tester.

My bad... MotoRad.