I've got a 1990 Firebird Formula. I'd like to do a full cooling system flush including the coolant in the engine cooling jackets. I need to replace the fan cooling switch (located on pass side block near knock sensor) during this process. So, I can drain there. My concern is the driver side of the engine. I believe I have identified the drain plug, but on my engine it looks like a hex bolt. I've seen photos and I believe it would normally be an Allen or Torx fitting. My concern is trying to pull this plug and having it break or finding it's been placed in the block to stop up a crossthreaded original drain bolt.

So, my question is, can I flush the cooling jackets by running water through the thermostat opening (top of engine) and disconnecting the lower water pump hose that connects to the radiator? Will that also flush the cooling jackets in the block?

Thanks!
David

 

Fan switch is in the head between the #6 & #8 spark plugs. Can't drain the block through the head. You can see it in the pic below and guess how hard it would be to make the water run uphill to escape that way.

The lower rad hose connects to the water pump. The water pump is pretty much at the top of the block. Still can't make the coolant drain upwards... so no, can't drain the block through that either.

The block drains are just above the oil pan rail... at the bottom of the block, lowest point, one on each side, at the exact midpoint of the block, front to rear. The pass side one is cleverly disguised as the knock sensor. The KS is I believe a 7/8" hex; an impact socket works GREAT. The driver's side one is a pipe plug. Not a bolt. It's a steel ¼" NPT plug. Not usually Torx or Allen thank Bozye. Usually comes out without too much of a fight if you use the right tool; which is, a 9/16" ½" drive 6-point impact socket. Don't try to use some regular weenie KROME socket; get an IMPACT one. Black. Thick, heavy-duty. 6-point.



You can see the hole there right above the oil pan, just behind the motor mount pad.

Replace the plug with a brass one from the hardware store. Put about 4 wraps of Teflon tape on it. Same for the knock sensor. Be careful not to overtighten the KS, doing so makes it over-sensitive and upsets its tuning, such that instead of responding narrowly to knock only, it responds to EVERYTHING. 12 - 15 ft-lbs is usually entirely enough.

 

What's the reason for attempting to be that thorough with the flushing? Changing 80% of the coolant is generally considered sufficient to renew the additive package that prevents corrosion, etc.

If it's a rusty mess then you can flush it 100x and you'll never get it all out. I did mine probably 25 times and it was still gross. Swapped out to a 400 HP Vortec and no more nasty coolant.

GD

 

Ahhh, I understand. I saw coolant coming from the fan switch when I loosened it getting ready to replace it during the flush. From underneath, it seemed lower and I didn't want to mess with the knock sensor if possible, but it looks like I'll have to. In order to flush the whole block. Thanks for the photo, that really helps. Thank you!

 

To answer your question, the car is new to me and it was a daily driver. So, these are the types of fluids that tend to get neglected. So, I've been going through and doing the things that probably haven't been done in a while. Doing a full flush and replacing the fan switch (not working), thermostat, rad cap, etc.

 

Why do you suggest putting in a new plug and not just using the existing one? Thanks!

 

Because the existing one is steel and makes a rusty mess; butt a brass one NEVER rusts and only costs like $3.

Don't be surprised incidentally, if you take the plugs out and no fluid emerges. Might need to rod the holes out with a coat hanger wire or something.

 

Ahhh, okay. I understand now! Thanks!

One more question, (sorry), won't the teflon tape on the knock sensor affect its working? If it is a one-wire connection, doesn't it need to ground out on the block like the fan switch?

 

Sort of. It's not really like that at all - it's a piezo-electric microphone - but in either case a couple wraps of teflon tape will not prevent it from grounding (seriously - two/three layers is enough - don't use half the roll). That's not how teflon tape works.

Myself - I prefer Loctite 545. But to each their own. Either will work.

GD

 

Awesome, thanks for the help!

 

I'm seeing some conflicting information regarding filling and bleeding the system.

Should I have the heater in the car on or off? Just set to hot and no fan? Set to hot and fan on? No fan, no heat set to hot?

Thanks!
David

 

Yours has a control valve so turn the heater on. You can run the heater fan but only on the lowest setting. You want the system to got hot, not use the heater core to cool itself down. There shouldn't be any significant bleeding required and the fan set point is above where the coolant will generally boil without pressure so fill it, start the engine, fill more till it's full, then cap it before it starts to get hot and run it till the fan cycles a few times (drive it if you need to, etc). Then allow to cool back to ambient, top off the radiator, and fill the overflow bottle to the minimum level. These systems are generally really easy to fill. There are no bleeder screws or anything like on some other GM's with the engine higher than the radiator.

GD

 

Thank you for the clarification, I appreciate it!

 

My expansion tank cap doesn't seem to stay on very tight. I can twist it on and pull it off if I pull up gently.

It's a new cap and the old one fit the same way.

Is that an issue?

 

Doesn't matter. It's vented anyway. These cars do not use pressurized overflow bottles.

GD

 

Awesome, thanks again for all the help! I'm new to these cars. I come from working on motorcycles, so this is a new adventure!