exhaust questions

[timninja]

I've got 2 questions:
1st one I need new exhaust for an I motor whats a good cheaper system?
2nd question,so far ive had bad cooling issues and I know m20s aren't bottle necked motors and flow well but could headers reduce trapped heat being less material on the motor to trap in heat?

[blocke]

Cooling issues are not going to be solved by modifying your exhaust setup.

Is the system bled properly? Radiator clogged? Thermostat stuck closed?

[mr.vang]

first thing before trying to fix the cooling problem, make sure you don't have a blown headgasket.

i have never heard of a header trapping heat causing the motor to overheat. its likely a bad thermostat, clutch fan, water pump or radiator

[timninja]

Sorry I asked the question wrong,would modifying my exhaust theoretically keep motor temp down?thoose stock manifolds seem like they'd trap heat.

[timninja]

But I am having heating issues,I just did my head gasket,I dont know how to check for a clogged radiator,my thermostat is 4 miles new and im not 100% ive bleed all of my air out

[blocke]

Think of it this way: BMW designed the engine and those manifolds to run perfectly.
If the manifolds had some design flaw that caused excess heat buildup, and caused engine overheating, then they would have caught it.
If you are running too hot, its not because of the way BMW designed the engine.

When you did your head gasket, what cooling components did you touch/replace?
Was it running hot before you did the HG?

-Also, "less material on the motor" would be less surface area. Less surface area= less cooling efficiency.

[jlevie]

Bleed the cooling system by:

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

Did you have the head surfaced and checked for cracks when you did the head gasket? If the radiator, expansion tank, cap, fan clutch, and hoses are over 10 years old they need replacing. The cooling system probably needs a chemical flush also.

[timninja]

I had the head straightend and checked for cracks all passed,I also need to replace my fan clutch but my water pump was done with my head gasket not even 10k ago.

So if I crack my expansion tank cap and I have a brief burst of air and constant low water,what does that typically mean?

[jlevie]

If you crack the expansion tank cap on a cold engine after the car has been driven and get a burst of air, there is a head gasket leak. If you constantly have to add coolant, either there is a leak in to cooling system (have a pressure test run) or there is a head gasket leak that is pumping air into the cooling system. Eventually the pressure will reach the point that the cap lifts and dumps coolant overboard. That may only happen while driving and leave no trace of where the coolant went.

[timninja]

Fuuaaahhhhck,its like 10k miles new,whats a better brand head gasket?

[jlevie]

I use the OE gasket & bolts like you get from a dealer.