Cooling System Flush on 1999 GTP

I'd like to flush my cooling system but can't find either block plugs. Anybody know where it is? I did a search on this forum but only found people saying it wasn't worth trying to find it.....does anybody disagree?

I see a bolt that goes into the side of the block that is right behind the starter....almost looks like a plug but it isn't, does anybody know what that bolt is for? The is one just like it on the backside (firewall side) of the engine.....

Let me know!!

Uh dumb question. :silly:

Why not use a Prestone flush kit that you can buy at Wally-World or from a local auto parts store? :ylsuper:

Uh dumb question. :silly:

Why not use a Prestone flush kit that you can buy at Wally-World or from a local auto parts store? :ylsuper:


Yeah everybody says that but I don't understand how they are any good? In order to get a 'true' 50/50 mix on antifreeze in the car you have to get enough water out of the block to get 50% of antifreeze back in....example, if you use the kit to flush the engine you will have 100% clean water in the engine, you can drain the radiator and add straight antifreeze but that isn't nearly enough antifreeze to make 50% again.....

Am I missing something? I think those kits are a bunch of junk....just my two cents.

You may be missing something. :tongue:

There are two block drain plugs located about the center of each side of the engine block below the cylinder heads and are a PITA to get to. If you desire to remove them have fun.

Here is a proven cooling system flush procedure that addresses the issue of getting as much water out of the system in order to get a proper mix. Try it out and let me know how it works out. Pay special attention to Step 5 in bold. You must use the Prestone Flush Kit. :grinyes:


Install the flush T from the Prestone Flush Kit in the heater return line hose.

1. With engine cool, remove radiator cap and drain the radiator.
a. Turn drain plug (lower left engine-side of radiator) counter clockwise about 1/8 of a turn (may require a little force if it's not been opened in awhile--be careful because it's plastic). Use the end of a 1/4" drive handle. Plug will extend slightly as it loosens. Be sure to have a container in-place to collect the antifreeze.
2. Let all the antifreeze drain into a container.
3. Remove, drain and clean the antifreeze overflow bottle. Reinstall bottle.
4. Hook up a garden hose to the flush T and turn water on (not too high or you can damage seals/gaskets with the pressure). When water starts to run from the drain plug, start the engine and turn the heater on (make sure you leave the water running during this process).
5. When water runs clear (about 5 - 10 minutes), turn off car, then turn off water, and remove hose from T and cap it. Let remaining water run from drain plug. (Note: Not all of water will be drained out of system mainly the engine block. What I do is hook up a drain hose to the T connector, start engine and let the water pump push water out of the system. As soon as you see no water coming out turn engine off, remove drain hose and cap off T connector).
6. Close radiator drain plug and fill radiator with a 50-50 mix of antifreeze/distilled water (or buy premixed).
7. Start vehicle and bring to operating temperature to make sure thermostat opens. Add additional mixture as necessary until full.
8. Reinstall radiator cap.
9. Release any trapped air in cooling system by turning the plug on the top of the thermostat housing (be careful not to burn yourself). When only coolant (no air) flows from the plug, close it. You may have to repeat this several times to get all of the trapped air. Raising the front end of the car where the radiator is higher than the engine helps bleeding.
10. Add additional coolant as necessary. Also, fill overflow bottle to recommended level. Be careful not to open radiator cap if hot. You may have to do this several times.
11. Check for leaks.
12. Properly dispose of old antifreeze.

Nice procedure,Bob. :ylsuper: You ought to put it in the tips/maint section. The method you laid out is the way I flush my cars except one thing. BTW, this sounds anal. I deal with very hard water where I live. After I close the drain plug, I remove the lower radiator hose from the radiator, get up off the ground, push down and up the fender a few times to get the last bit of water out of the block and anything that dribbled out of the heater core into the engine. I then re-connect the hose and proceed with the 50/50 fill.

You may be missing something. :tongue:

There are two block drain plugs located about the center of each side of the engine block below the cylinder heads and are a PITA to get to. If you desire to remove them have fun.

Here is a proven cooling system flush procedure that addresses the issue of getting as much water out of the system in order to get a proper mix. Try it out and let me know how it works out. Pay special attention to Step 5 in bold. You must use the Prestone Flush Kit. :grinyes:


Install the flush T from the Prestone Flush Kit in the heater return line hose.

1. With engine cool, remove radiator cap and drain the radiator.
a. Turn drain plug (lower left engine-side of radiator) counter clockwise about 1/8 of a turn (may require a little force if it's not been opened in awhile--be careful because it's plastic). Use the end of a 1/4" drive handle. Plug will extend slightly as it loosens. Be sure to have a container in-place to collect the antifreeze.
2. Let all the antifreeze drain into a container.
3. Remove, drain and clean the antifreeze overflow bottle. Reinstall bottle.
4. Hook up a garden hose to the flush T and turn water on (not too high or you can damage seals/gaskets with the pressure). When water starts to run from the drain plug, start the engine and turn the heater on (make sure you leave the water running during this process).
5. When water runs clear (about 5 - 10 minutes), turn off car, then turn off water, and remove hose from T and cap it. Let remaining water run from drain plug. (Note: Not all of water will be drained out of system mainly the engine block. What I do is hook up a drain hose to the T connector, start engine and let the water pump push water out of the system. As soon as you see no water coming out turn engine off, remove drain hose and cap off T connector).
6. Close radiator drain plug and fill radiator with a 50-50 mix of antifreeze/distilled water (or buy premixed).
7. Start vehicle and bring to operating temperature to make sure thermostat opens. Add additional mixture as necessary until full.
8. Reinstall radiator cap.
9. Release any trapped air in cooling system by turning the plug on the top of the thermostat housing (be careful not to burn yourself). When only coolant (no air) flows from the plug, close it. You may have to repeat this several times to get all of the trapped air. Raising the front end of the car where the radiator is higher than the engine helps bleeding.
10. Add additional coolant as necessary. Also, fill overflow bottle to recommended level. Be careful not to open radiator cap if hot. You may have to do this several times.
11. Check for leaks.
12. Properly dispose of old antifreeze.


I spent a lot of time looking on the front side of the engine today and didn't see any drain plugs, I even took the starter off the car. It must be under the exhaust manifold somewhere that I can't see it.

Your method seems like it is the way that you'd have to do it with a 'T' valve but I'm still not convinced its a good way.....seems strange to me that the best way to drain my cooling system is to install a drain hose to a aftermarket 'T' valve and run my cooling system dry. I'm not saying your way is bad you're just working with what you've got!! I think of this 'T' valve as a weak point in the system and am trying to aviod putting it in. Thanks for your advice.

I wish to flush my cooling system before it gets too cold. Can you identify the "return hose" on a 98GT? Also, how can I remove the overflow tank for cleaning?