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More coolant questions

DanC

Well-known member
Joined
Jun 12, 2002
Messages
74
Location
Bradford, MA USA
Corvette
1993 Ruby Red Coupe
When I changed the coolant in my 93 LT1 last August, I was able to purchase coolant that met the General Motors spec 1825-M5 that's noted in the factory service manual for this engine.

Just got back from shopping for coolant, and the specs on the package now are mostly "Meets ASTMD-3306 and ASTMD 4985".

Found one that also had "GM1825M" with the others (the 5 is missing at the end, significant??).

With all the horror stories floating around about DexCool and others with compatibility problems, what do I use to top off the system?

Are the new specs similar to motor oil ratings? Backward compatible?

I'm so confused...

Thanks,
 

compyelc4

Well-known member
Joined
May 1, 2002
Messages
609
Location
Dayton, Ohio
Corvette
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
1. Why does the system need "topping off".
2. How many years since fluid was last changed.
3. What color is the coolant in there now?
 

vee93

Well-known member
Joined
Nov 15, 2002
Messages
585
Location
Mississippi
Corvette
1993 Medium Quasar Blue Metallic Coupe
You have a '93. So why are you even looking at DexCool? What's wrong with good ole Prestone? You said you changed it last August... What'd you use then? I don't really see the need for "shopping around" for coolant. Get the Prestone, follow the specs in your owner's manual and be done with it.
 

c4cruiser

Well-known member
Joined
Feb 22, 2002
Messages
971
Location
Lacey, WA USA
Corvette
87 Gold Z52 Coupe 02 EB Z51 Supercharged Coupe
Your 93 uses the green ethlyene glycol coolant that has been around for years. Prestone is as good as any of the green coolants and you can use other brands if necessary. Most brands of green coolant can be mixed so don't worry too much about compatibility.

BTW, if you bought concentrtated green coolant, did you add distilled water to make up the FSM Recommended 50-50 mix??

There is no real reason to switch to the orange/red Dex-Cool in the eearlier cars. While it can be done, it's very important to insure that all traces of the green coolant is flushed from the cooling system. The green and red coolants are not compatible and a mix will cause a brown sludge to form and restrict cooling.
 
Joined
Jan 15, 2004
Messages
2,240
Location
Northern Indiana
Corvette
1987 Z52 Black Convertible
Yeah agree I run Prestone in my 87 and have never had any problems. Its been a year and the coolant still looks like brand new. I would recommend flushing it every year though. Mix it close to 50/50 (I run 60% water 40% antifreeze). Good luck.
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
Why are you adding

The question is were is the coolant going. On my 93 I was losing fluid from the water pump over the Opti. In my case when the engine was running and up to temp I could see a fine mist coming off the right front side of the engine. Further inspection showed a green stripe on the power steering pump housing. In the two years since I replaced the pump I have not added any fluid to the overflow tank. By the way the failure of my pump was the bearing that goes on the camshaft. It and the seal were in shreds.:blue:
 

DanC

Well-known member
Joined
Jun 12, 2002
Messages
74
Location
Bradford, MA USA
Corvette
1993 Ruby Red Coupe
Thanks for the replies. Maybe I could have been clearer with my question.

I changed the coolant last August, using a coolant I purchased from my local parts store that specifically stated it met the GM 1825-M5 spec (green) that's noted in the factory service manual for this engine.

I used a 50/50 mix of distilled water and coolant, but was a little short to top off the recovery tank to the full mark.

After much procrastination, I went back to buy another gallon last week. That's where my problem started. None of the coolants on the shelf, including the green Prestone, mention the GM 1825-M5 spec, likely since it's been superceded by one of the ASTMD specs.

I just want to add what is 100% compatible with what's in there.

BTW, I changed the coolant when I replaced the water pump and opti with a new GM water pump and a Dynaspark distributor.
 

c4cruiser

Well-known member
Joined
Feb 22, 2002
Messages
971
Location
Lacey, WA USA
Corvette
87 Gold Z52 Coupe 02 EB Z51 Supercharged Coupe
You will be OK with any good brand of ethylene glycol green coolant especially if you are not adding a lot to the system. For what it sounds like you need, I would not worry too much about trying to find a coolant with the GM standard listed on it. Prestone, Peak, and other "green" coolants will work fine.

When you check the overflow tank, do it when the engine is cold and only fill the plastic tank to the "Cold" line. The tank needs room for hot coolant to expand and flow down from the expansion tank down to the overflow tank. That coolant will be sucked back up to the expansion tank as the system cools down.
 

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