Coolant choices

I’m about to do my 2 year coolant flush, but am really confused with the new coolants on the market.

My car came with green coolant. For past five years, I’ve been using Zerex original green, along with distilled water. I assume its IAT. It says low silicate formula. I now think it may have phosphates?

So i just bought Prestone instead. It says it works with IAT coolants, and has cor guard tech, is that not phosphate based? But its yellow.

Is there a green phosphate free iat coolant out there??

The Prestone is HOAT, phosphate free. AF2000. It claims it can mix with IAT. I may try to get out as much green as i can and try it out.

Reading archives, it seems the orange OAT is the one not to use.

The Zerex original green says this:
PHOSPHATE ADDITIVES SAFEGUARD AGAINST CORROSION, SCALE AND RUST while protecting all cooling system metals (including aluminum)

Zerex G05 is made for modern aluminum engines. It is pale yellow. I use it in my XJS and Mercedes.

Thanks. Good to know. I’ve done some reading, and the Zerex G05 looks like the way to go.

As I’ll be switching from green to yellow G05 this weekend, I want to try and get out as much green coolant as I can. Mixing G05 with green just lowers the G05 long term guarantees of corrosion inhibitors, and I’ll be replacing coolant again within a year when I pull radiator, so not critical.

I will be disconnecting lower radiator hose. I’ll also siphon out catch tank in left fender well. Then I’ll apply some vacuum to heater valve and tilt car forward, will this empty heater core and block?

Any other tricks, without having to flush (I’ll do that next year)

Thank you!

Greg, the heater valve, with no vacuum applied, is N/O.Blow the heater out with compressed air. I doubt that “tilting” will accomplish much.


Thanks, i always forget how that heater valve works. Will fire up the compressor.

I really like the idea of switching to Zerex G05 now. Claims 5 years life, but I’ll still change every two years. The green IAT stuff is getting harder and harder to find, and i think most contain phosphates? G05 is phosphate free HOAT. I think what makes it hybrid and compatible is that it has a low silicate content. Its $22/gal, so a bit more expensive, but over two years that’s nothing.

I always add a bottle of Redline Water Wetter too.

I’ve always used Prestone, no issues and drop in a bottle or two of Hyperlube super coolant wetter,
Added benefit they’re even from your town.

Got it changed to G05, blew out heater core lines. Took about four gallons total (50/50). The green is probably fine, but i like the idea of changing something every two years that says it can go five years. And like i said, it’s hard to find green these days.

When i pull my radiator and get it re-cored end of this year, I’m going to ask if they can install a drain plug (can it be done?). Such a pain removing that lower hose at radiator. I’ll also give the block a good back flush.

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If you decide to buy a Wizard radiator, they have an extra threaded fitting below the trans cooler, to which you can add a short length of 3/8 hose, an elbow, and finally a drain valve located where it can be reached from below. Probably why I refresh my coolant annually!

Arguably one of the first jobs I did when I got the car. My big mistake was to not get a drain plug installed. The radiator was operating at about 40% efficiency according to my radiator guy between side part half plugged with bars and fins being corroded. The temp gauge would really start to get up there.
I would say I probably change coolant every three years. It’s a messy job pain in the butt job without the drain plug.
I still add the green Hyper Lube with the Prestone to reduce water surface tension and corrosion protection. Was thinking about doing the Lutz mod but everything seems to be working fine now.
On that note I’m going to swap out my electric fan. I have the Spal fan still in the box. I guess I’m going to have to remove the fan shroud (again). It’s been a while since I pulled the radiator. Do I need to remove the top section by the banjo bolt to get the shroud off?

I’m leaning towards a recore instead of a Wizards…Although may be hard to tell them where exactly to put tap with it out of car…I’ll look into it.

Anybody needing to drain coolant like me via lower hose, it’s a pain, but not crazy. When I replaced hoses, I positioned my clamp so that a very long extension with 8mm socket and swivel would reach from top. Once the clamp is loose, the hard part is trying to break free the hose. I can only get my left hand down there, and can only use hand strength. EVENTUALLY it will break free. Then you can wiggle/pull hose off of radiator outlet. Make sure you have something large to catch the waterfall of coolant underneath. Getting the hose back on isn’t difficult, but trying to get the clamp in a position so you can tighten it up is tough, as you can’t get two hands in there. Patience.

It’s been a few years since I replaced my electric fan, but I remember removing the shroud to replace the fan wasn’t too difficult. Only the bolts holding both shrouds to the radiator. Bottom bolts are a bit of a pain, but accessible. Banjo bolt and other stuff didn’t need to come off, I think. The new fan will do an amazing job compared to the old original fan. Mine only takes 1/2 the time to cool radiator enough to shut off.

I’ve been lucky, my original radiator still seems to cool fine, although I drive in Seattle weather, and if it’s more than 85F, I just don’t drive the car (No A/C). For all I know, the radiator was serviced by previous owners, not sure. I will be doing it later this year as part of my restoration. Want things at 100% so I can take longer drives without worrying.

So many different makes of that coolant additive. Redline Water Wetter is what I use, I really like Redline products I guess.

A few years ago I did a coolant swap to the Evans waterless. Jacked the rear-end up to a severe nose down attitude.
After gravity draining at the lower radiator hoseI used wet/dry shop vacuum to get more. I rigged up some smaller tubing (that would slide into the heater tubing) to the vacuum by duct taping the tubing to the vacuum crevice tool…and sucked out more fluid at the heater outlet.
After about 6 years with Evans I switched back to Green Prestone. The viscosity of the Evans was always resulting in seeps and drips. Back to Prestone and the seeps and drips are gone.


Greg, You can add a drain plug to the existing radiator.

Great, thanks! You know, your posts will live on forever like the book. I find them very helpful with the photos, and then see you did this over 15 years ago!

And it looks like you put it lower right side facing engine?

I guess i could paint a mark there before i pull radiator so i know exactly where to drill.

I assume it can’t be done on bottom of radiator?

Greg, you would need a flat spot at the bottom of the radiator to solder the nipple. In addition it would have to be protected from road debris. Juice not worth the squeeze as they say. A location on the side of the radiator amount an inch from the bottom is acceptable. If you are concerned about not getting all the antifreeze out of the bottom of the radiator, then flush with water before refilling.

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When I recently had my radiator recored, I had the guy add a valve for me. Bottom right hand corner. Didn’t even charge me extra for it!

I highly recommend recoring. It will end up costing about the same as the Wizard, but the OEM radiator is pretty solid. Recoring it virtually guarantees a perfectly smooth reinstall and years of reliable cooling.