Cooling system multiple questions

[MattBimmer]

Hey guys,
I wanna ask several questions because I am hoping to get the calling system running better before having to water pump and the timing belt.

1st. If my 87 m20 325i (auto) temp gauge rides a little over 1/2 on the temp gauge something is wrong correct? It's like maybe 3/5 or less not to the 3/4 dash. I have heard some that say that it's okay but others who say that's no beuno.

2nd. How do you flush the radiator well. I plan to take the radiator out and clean the fins of the radiator to make sure there isn't gunk buildup on the front preventing air flow. While its out I wanna make sure there weren't any blockages clogs by flushing the system. (It has a metal connecting hose that looks like a power steering/AC style hose connected to the radiator. I am wondering if that may be the old cooling system for auto trannys). Anything special about disconnecting that?

3rd. What temp thermostat would you guys run. I researched it, but I feel like 180 would be right but...just want more opinions.

4th. What is a solid idle for you guys. My idle has been sitting at 650rpm and can get down to about 500 sometimes.


Thank you all for your help. This is my first time working with the m20 I have been doing m42 for the longest but first time working with the 6 cyclinder

[lcoleman]

1. yes, should always be at 1/2 or less
2. use a hose, watch the gunk come out the other end. flush both ways a couple of times
3. I would use factory, I believe it's 200deg (82C?)
4. *shrug* with MS, I'm just happy when it does idle, lol

[jlevie]

(1) At 45mph or greater the gauge should indicate about half way between the quarter and half marks if the cooling system is working properly and an 80C thermostat is installed. In stop and go traffic (with or without the AC being on) the needle may rise to the half way point, or perhaps a needle's width above when AC is on in hot weather.

(2) There is essentially no good way to flush the internals of the radiator, or to know if/when it is clean. The hoses that connect to the side of this radiator are for the transmission cooler. You will loose some fluid when those are disconnected.

(3) Use a stock 80C thermostat.

(4) The engine should idle at 750rpm.

A good rule of thumb for a cooling system with plastic parts is replacement every 10yr/100k. In this case that means the radiator, expansion tank, cap, thermostat, water pump, fan clutch, and all hoses. Parts of the system may last longer, but if not replaced there is the risk of sudden and complete cooling system failure. At which point you wind up replacing the cooling system and then repairing the engine damage caused by the overheat. Scheduled replacement dramatically reduces that risk, ultimate cost, and keeps the cooling system in good condition.

For the idle, work through what follows without skipping any steps to fix the low idle problem.

Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn't eliminate the
possibility. Only a smoke test will really work.

Once the possibility of intake leaks is eliminated, the ICV needs to be
removed and cleaned with carb cleaner until the vane inside moves freely. When
the ignition is switched on you should be able to feel vibration from the
ICV. If no vibration the ICV is bad, there's a problem with its wiring or
connector, there's a problem with the TPS, or the DME (or Idle Control Module
(ICM) on an ETA car) is faulty.

For the DME (or ICM) to control idle, the idle switch in the TPS must work
correctly. The switch should close when the throttle stop is 0.030-0.060" off
the idle stop screw. Hearing a click doesn't mean the TPS is working. Check
with a meter or test light.

The fuel system should be tested via the suite of tests in the Bentley manual
as invalid rail pressure can be a contributor to idle and starting problems. A
simple injector check is to pull the injectors, jumper the fuel relay to run
the pump, and see if the injectors are leaking. You can also point the
injectors into a towel, remove the coil wire, and crank the engine to see if
all of the injectors appear to be spraying in a similar fashion. The best
approach to possible injector problems is to have the injectors cleaned and
flow tested. Since raw fuel can or will be released in these tests, have a
fire extinguisher handy.

While a bad check valve in the high pressure pump can result in longer than
normal cranking, if the fuel system is working as it is supposed to the rail
will reach normal pressure in a few turns of the engine. A weak pump, clogged
filter or leaking FPR in conjunction with a failed check valve can result in
longer cranking and/or idle poroblems.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

The AFM can be a contributor. If the vane doesn't move freely or the
resistance track is worn the DME may be receiving invalid data from the
AFM. And if someone has fiddled with the bypass air adjustment the DME may be
unable to stabilize idle. The bypass air adjustment should only be adjusted
per the procedure in the Bentley and with an exhaust gas analyzer. And even
then everything else associated with engine management has to first be
operating properly. If the AFM becomes a suspect, replacement with a good used
unit is the best approach.

Improperly adjusted or malfunctioning valves will affect idle and starting. As
can compression issues from ring or cylinder wear. A valve adjustment is
called for every 15k. A useful diagnostic is to run compression (dry and wet)
and leak down tests on the engine. Aged ignition wires, plugs, distributor
cap, or rotor can cause problems. Insulation does break down with time and
heat. And since the youngest E30 is going on 20 years old, if the ignition
system is original or the plugs are old replacement is indicated.

Although not usually a problem, a bad DME temp sensor is a possibility. That
generally won't cause an unstable idle, but can cause hard cold or hard hot
starts and/or a rough idle. As can problems with the timing reference
sensors. Although not commonly encountered, a bad harmonic balancer on an
M20B25 or M30 engine will cause problems.

When all other possibilities have been eliminated and idle or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

In many cases the cause of problems will be a combination of factors. So it is
important to test and repair all of the possible causes.