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Replacing the coolant

Old 07-07-2018, 07:26 PM
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turbobuick33
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Default Replacing the coolant

I want to replace the coolant on my 96 C4. How many gallons do I need to fill it up? I'm guessing 2 gallons? Are there any plugs on the engine to remove to get more coolant out of the engine?
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Old 07-07-2018, 08:10 PM
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OK - the C4 cooling system holds about 16 quarts - so 2 gallons of full strength coolant and 2 gallons of distilled water should do the trick.

The "right way" to do the job is to drain the rad - then to pull Both knock sensors. (note - there is no know way to do the knock sensor removal job "cleanly" - the old coolant is going to go all over the place - including on you - so don't do the job when the coolant is 200 deg. A big pan will catch "most" of the old coolant - but plan on making a mess... The good thing is that if you do it outside - you can hose down the mess you make. I also try to suck out the coolant reservoir just to get rid of as much of the old stuff as possible.

Many C4 owners have reported that the stuff that comes out of the Block drains towards the end is near black. I've seen this myself on one C4 that I bought used. If that is the case with yours - you may wish to consider undoing the two heater hose connections, and flushing the heater core out with a garden hose.

Once you get the system drained out - put everything back together and add the coolant and water - then start it up, and check for leaks. I try to repeatedly squeeze the lower coolant hose as I fill the system - it seems to help minimize air bubbles - but the LT1/LT4 motors are notorious for having air pockets in the cooling systems. If you can't get 16 quarts or so in after a full drain - you have an air pocket somewhere.... BTW - if the rad hoses are original - you might want to consider changing them - they are more than 20 years old....

GOOD LUCK !!!
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Old 07-07-2018, 09:17 PM
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I plan on buying 50/50 mix. So it takes about 4 gallons? On the LT4 is there 1 or 2 knock sensors? Where is the knock sensor located?
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Old 07-08-2018, 02:46 PM
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Originally Posted by turbobuick33 View Post
I plan on buying 50/50 mix. So it takes about 4 gallons? On the LT4 is there 1 or 2 knock sensors? Where is the knock sensor located?
Yep - 4 gallons of 50/50 mix. (The 2 gallons of full strength and 2 gallons of distilled water route is typically less expensive - but your car - your call).

The knock sensors are threaded into what used to be called the block drain holes. Roughly center of the engine - maybe an inch or so above the oil pan gasket - one on each side... (see attached pic).
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Old 07-08-2018, 04:39 PM
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When I pulled my knock sensors nothing came out. Had to poke the hole with a screwdriver (#2 Phillips works) to break up a crusty blockage. Once I broke that out the flood came.
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Old 07-08-2018, 04:57 PM
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Should I use dex cool or the green coolant? I've heard many say dex cool isn't a good coolant to use. Many switch to the green coolant. What do you guys think?
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Old 07-08-2018, 05:27 PM
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your 96 came with dex-cool... use it again.

Dex is good stuff since the formula changed a decade+ ago... Its only REALLY bad when its mixed with green coolant OR when you let it go to long.

Get on a 5 year schedule of changing it.
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Old 07-09-2018, 12:54 AM
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If you pull those knock sensors to drain more coolant, do you have to put something on the threads when reinstalling to prevent leaks?
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Old 07-09-2018, 07:31 AM
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Use Distilled water only and Xerex full strenght G20 only. Cover your opti when purging for air for water will destroy it.
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Old 07-09-2018, 09:05 AM
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Originally Posted by fake View Post
Use Distilled water only and Xerex full strenght G20 only.
Pssst! He's using premix.
Originally Posted by turbobuick33 View Post
I plan on buying 50/50 mix. So it takes about 4 gallons? On the LT4 is there 1 or 2 knock sensors? Where is the knock sensor located?
And pleny of other coolants will work just fine, besides "Xerex G20 only".

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Old 07-09-2018, 11:49 AM
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Originally Posted by Maldini View Post
If you pull those knock sensors to drain more coolant, do you have to put something on the threads when reinstalling to prevent leaks?
I was going to ask the same question. I'm thinking some white permatex thread sealant.

Last edited by turbobuick33; 07-09-2018 at 11:50 AM.
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Old 07-09-2018, 12:01 PM
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Remember to torque the new knock (rock auto has them cheap) sensors to 14 ft-lbs, more than that and they are useless. Can some confirm 14 ft-lbs...I know the 14 is right, just want to confirm "ft-lbs"
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Old 07-09-2018, 12:15 PM
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14 lb-ft is correct for the knock sensors, and an important spec for doing the job properly.
I would not use any thread sealant on the knock sensors because they ground to the block. I used a bit of anti-seize (copper) when reinstalling the original sensors. With the correct torque installation they are not leaking.
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Old 07-09-2018, 12:18 PM
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That was going to be my next question, is whether or not the originals can be used. Sounds like it would be ok to do this.
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Old 07-09-2018, 12:34 PM
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Originally Posted by Maldini View Post
That was going to be my next question, is whether or not the originals can be used. Sounds like it would be ok to do this.
Yes. Some will say "they are decades old, you should replace them." But these parts are not known for failure. So unless the connectors are broken or they are otherwise damaged, you can re-use them. My 1995 LT1 runs very strong with the original knock sensors and I know for sure they are working properly.
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Old 07-09-2018, 06:08 PM
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Originally Posted by rjacobs View Post
your 96 came with dex-cool... use it again.

Dex is good stuff since the formula changed a decade+ ago... Its only REALLY bad when its mixed with green coolant OR when you let it go to long.

Get on a 5 year schedule of changing it.


It's interesting - over the years Dex-Cool has gotten a bad reputation - but there are literally millions of GM produced cars driving around with it, and it seems that very very few have problems. I use Dex-Cool on cars that came with Dex Cool - and have not had any problems. I've even converted an older Volvo over to use Dex-Cool and zero problems there. When I was doing that conversion - I spoke with one of the Engineers at Havoline, and according to this guy the only real problems they saw in their testing were that some German cars build in the 1990's used a rubber in the cooling system hoses that the Dex-Cool didn't get along with real well - other than that - as long as you did a VERY thorough flush to get the old stuff out of the system - no problems.

Most of the problems I have heard ascribed to Dex-Cool had to do with combining Dex-Cool with the "conventional" green anti-freeze - which is just NOT a good idea !!! No question in my mind that Dex-Cool is an advance over the old "green" ethylene glycol anti-freeze that typically had a two year life. Some of the newer extended life coolants out there may be better than Dex-Cool - but if you notice - GM hasn't changed to any of them - and they're the ones who have to warranty the cooling system in their cars - so if there was something that was really better (and similarly priced) - I'd bet that they'd be going to it...

And yes - I agree - sometimes when you pull the knock sensor - nothing will come out - when that happens you have to either puncture a small seal or poke through the crud that's accrued over time - just give it a tap with a small punch or a small screwdriver and that should remedy the problem. I put a little bit of pipe sealant on my knock sensors when re-installing. Typically the impedance of the knock sensor is about a million ohms - so I'm not too too terribly concerned about adding a little bit of resistance. The factory did put a sealant n the knock sensor threads when they built the cars..
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Old 07-09-2018, 06:13 PM
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Originally Posted by rjacobs View Post
your 96 came with dex-cool... use it again.

.

Get on a 5 year schedule of changing it.
One other point. To grossly oversimplify things - the stuff in anti-freeze that keeps the coolant from freezing doesn't wear out. But that's not all that is in anti-freeze - there are a number of other things in there - and some of those additives are put there to protect against corrosion. They do this well - but they are sacrificial by their very nature - so over time - they do "lose their effectiveness" - so that's why we replace anti-freeze.

Rather than doing a 5 year full system flush - I do a rad drain and refill every couple of years. That gets nice new corrosion protection additives into the system, and it's a LOT easier to do the radiator flush than the full system drain and refill. On a neglected systems - you still need to do the full drain and refill - but once you get the system back into shape - consider doing just the rad drain and refill every two years or so...
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Old 09-15-2018, 08:26 AM
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When adding coolant does the thermostat housing fitting need to be opened? Would you use O'Reilly brand dex cool 50/50?

Last edited by turbobuick33; 09-15-2018 at 08:31 AM.
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Old 09-15-2018, 09:00 PM
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Originally Posted by turbobuick33 View Post
When adding coolant does the thermostat housing fitting need to be opened? Would you use O'Reilly brand dex cool 50/50?
I routinely use the Prestone version of Dex-Cool commonly available at Wal Mart. I can't imagine the O'Reilly's brand is all that much different.... Dex-Cool was developed by Havoline, and they were the only producer for a number of years - now you can't find the Havoline stuff it you try. The one thing I'm fairly sure of is that any brank of new Dex-Cool is better than Dex cool that's been in use for three, four or five years !!!

As far as refilling the system - there are as many ways to do it as there are people doing it. I've never had to open the bleeder screws, but others swear by that technique. Try to put back in roughly the same amount you took out, and watch the temp gauge for very fast increases (indicating a bubble). I always carry some water / anti-freeze with me right after a coolant drain fill - "just in case". Bu truthfully - I've had more problems getting air bubbles out of a V-6 Camry's cooling system than any C4.


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Old 09-17-2018, 11:52 AM
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I fill with the bleeder closed, until the system is topped. Then I open the bleeder, air will come out for a couple seconds, then I get coolant. I close it quick, re-top the system, and I'm done. Minimal spill, minimal time....easy.
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