Can I mix Prestone (green) and Shell Extended Life (orange) coolant?

The coolant on my port engine seems to go low (that's another problem), and yesterday the port engine overheated (alarm went off) while out on the water. A friend that was nearby brought me a gallon of coolant. I added it, and made it back OK. I have ShellZone extended life coolant (orange) in the engines, and I added Prestone (green). Am I OK with mixing these or will it cause problems? Merc 8.1 gas engines, fresh water cooled, inboard/V-Drives, 2004 Sundancer 340. Thank you.

Joe Lichtenberg said:

The coolant on my port engine seems to go low (that's another problem), and yesterday the port engine overheated (alarm went off) while out on the water. A friend that was nearby brought me a gallon of coolant. I added it, and made it back OK. I have ShellZone extended life coolant (orange) in the engines, and I added Prestone (green). Am I OK with mixing these or will it cause problems? Merc 8.1 gas engines, fresh water cooled, inboard/V-Drives, 2004 Sundancer 340. Thank you.

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I have always been told no, do not mix the 2. Not sure why tho

Joe Lichtenberg said:

The coolant on my port engine seems to go low (that's another problem), and yesterday the port engine overheated (alarm went off) while out on the water. A friend that was nearby brought me a gallon of coolant. I added it, and made it back OK. I have ShellZone extended life coolant (orange) in the engines, and I added Prestone (green). Am I OK with mixing these or will it cause problems? Merc 8.1 gas engines, fresh water cooled, inboard/V-Drives, 2004 Sundancer 340. Thank you.

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I cannot speak to your particular mix but I have seen the results in a friend's boat The results of mixing green and orange in his case was a gelatinous goop that needed to be flushed out..

Find the cause of your coolant leak! That leak could easily be a symptom of something so serious that it causes engine failure. Saving a few bucks on topping up coolant could cost you $10K. And don’t wait in hope of getting a few more weekends out of it.

In general, green and orange with a little time and heat turn to jello. Drain, flush, and refill.

It's well documented in GMs, do not mix dexcool with green coolant. I'd drain it all out, flush, refill and find the leak.

My only coolant leak was in the main heat exchanger for the engine. It wouldn't show itself under normal pressure testing since the tube's small split would only open up enough to leak when up to engine temps. Testing was done at room temps. My first thought was a leaking head gasket, but a good and wise friend said "more likely to be a leak in a heat exchanger". Still took one boat buck to replace, but all good after that.

Nothing wrong with dexcool, but once filled with dexcool I'd always use dexcool to avoid gel forming and causing blockages in small passages. I've read that the big issue with dexcool GM had on some engines wasn't the coolant, but the installation of improper OEM head gasket materials which were broken down by the dexcool. People freaked out on the dexcool, drained and refilled with green (easier than replacing the head gaskets with proper ones). Problem was that it's almost impossible to get rid of all the coolant so the green/orange mix gel issue was sometimes detrimental to the engine's longevity.

I agree with Creekwood. Find and repair the cause or risk major failure. You should of added straight water to the Dexcool instead of green af. Flush the system now.

Several auto parts stores will rent you a block testing kit to check your cooling system. The kits usually include a bit that goes on in place of a radiator cap and you fill it with a fluid that will change color in the presence of exhaust gasses as the engine runs. The second part is a small hand pump with a pressure gauge so that you can pressurize the system while the engine is cold once you've ruled out a blown head gasket. You watch the gauge and if it goes down there is for sure a leak. While its pressurized you can look for the leak. It's not a difficult diagnostic for a shadetree mechanic to do themselves.

Also you should never mix the orange and green coolants ever.

The green coolant is an inorganic additive technology (IAT). With this type of coolant, phosphates along with silicates are added to ethylene glycol. This helps to protect the metals that are in the vehicle’s cooling systems from becoming corroded. There are some IAT coolants that use propylene glycol instead of ethylene glycol.

The orange coolants are organic acid technologies (OAT). These were created for newer vehicles that had more nylon and aluminum parts in them. OAT coolants use organic acids in order to prevent corrosion.

The two chemicals will react with each other when mixed and create a jelly like substance that will block the flow of coolant through the cooling system and cause expensive repairs and overheating. FLUSH THE MIXTURE YOU HAVE ALREADY MADE IMMEDIATELY.

Thank you everyone for your replies.

Joe.