M20B20 bleeding coolant system

[DarioStraightSix]

I've just replaced the timing belt and water pump on my '83 320i. Once i put everything back together i started bleeding the cooling system. Looking some guides online i thought it was a straightforward job...i've had some trouble instead.

I turned the heater to maximum,i loosen a bit the bleeding screw on the thermostat housing and i started to fill the expansion tank until the maximum level. Then i tightened again the screw and i turned the key.
The engine axpired the fluid as expected and then i add a bit.
When the temperature gauge went to the middle i loosen again the bleeding screw. A bit of air bubbles went out. I tight again once i've seen that went out only fluid. And here starts the problem : temperature went over the middle and the coolant in the expansion tank started to boil...at that point i stopped the engine. Fortunally i putted the cap on expansion tank because a lot of hot water arrived in it from the engine.
I bleeded the steam with the bleeding screw.

The thermostat works i think because the radiator was warm and the hose from the thermostat to the bottom of the radiator too. The other hoses were hotter,but i think it should be normal. The fan works too,i didn't do the newspaper test but it seems to work.

What went wrong? Thanks in advance and sorry if i did some grammar orrors.

[Brianmoooore]

Was there heat coming from the heater?

[DarioStraightSix]

Was there heat coming from the heater?

I didn't check the heater. I've got the blower motor out of the car to replace the bearings that are worn out.

[Brianmoooore]

It's most important that you monitor the heater output as you start up after cooling system work, to ensure that air with some heat in it begins to emerge after a minute or so. These engines are prone to air locks at the back of the head, which stop the flow in the heater circuit, and can easily crack the cylinder head.
The airlock is easily cleared by filling the coolant bottle right up, removing the top heater heater hose at the bulkhead under the bonnet, and pushing it back on with coolant flowing slowly from the pipe and the stub.

[DarioStraightSix]

Many many thanks Brianmoooore! I really appreciate your help!

So,if i understand well,now i've got to unclamp the upper heater hose and fill the expansion tank untill i'll see coolant flowing out of the heater hose. Am i right?

[Brianmoooore]

Overfill the coolant bottle before you start. It'll sort its own level out afterwards by blowing excess out of the overflow tube.
The flow from the open pipes will be quite slow, but on an M20 can be speeded up by removing the pressure cap, laying one hand flat across the top, putting the free end of the overflow hose in your mouth, and blowing gently to pressurise the system slightly.

[DarioStraightSix]

If i'm right,the heater hoses are next to the brake master cylinder on (for me,lhd car) driver side. There are only the attachments tapped with some kind of caps,no hoses...it means that somebody in the past,for a reason that i don't know eliminated the heater
I don't know if this has something to do with the shitty methane gas system that the car has. I never used it,i only run it with petrol. I want to eliminate everything as soon as possible.

At this point what to do? Try again hoping to bleed out all the air in the system? I'm a bit scared for the head gasket doing too much attempts...

[Brianmoooore]

If i'm right,the heater hoses are next to the brake master cylinder on (for me,lhd car) driver side.

Master cylinder and servo are in the same place on RH drive cars, operated by two bell cranks and a pull rod.

There are only the attachments tapped with some kind of caps,no hoses...it means that somebody in the past,for a reason that i don't know eliminated the heater

There was a safety recall in 1996, regarding excessive pressure in the cooling system. The heater valve on the LH side of the heater box could fail and spray superheated water over the legs of the occupant of the LH seat.
The solution in the UK was a modified pressure cap for the coolant bottle, but US cars got a thermostatic bypass for the heater pipes as well. I don't know whether your country got this as well, or what it actually looks like.

I don't know if this has something to do with the shitty methane gas system that the car has. I never used it,i only run it with petrol. I want to eliminate everything as soon as possible.

Methane or Propane? Propane is a far superior fuel to petrol to run a car on, eliminating oil contamination and bore wash, resulting in a vastly increased life of the engine. I run all my cars on it!
Propane needs a hot water supply to the device that changes it from a liquid to a gas, and this is usually plumbed into the heater circuit, normally by tee pieces, but occasionally in series.
I suppose, if the climate where you live is such that you'd never need the heater, it could be disconnected completely, and the pipes just connected to the gas reducer. You'll still have the hoses, so they can be bled instead.

At this point what to do? Try again hoping to bleed out all the air in the system? I'm a bit scared for the head gasket doing too much attempts...

It's not the head gasket that fails, it's the head itself that cracks. Fortunately the 2.0 litre head is more robust than the 2.5 litre version

[DarioStraightSix]

Thanks!! You're very kind sir!

The gas used is methane,is quite common in Italy for two reasons :

_ methane is chaper than petrol ;

_ in some areas old car are banned for their emission level,and once you put an LPG or methane system the car become an ecologic vehicle.

In my zone i've got no pollution restrictions and then mine is considered an historic vehicle so i can go everywhere everytime. The problem with methane is that the performance are very very poor. When you turn to petrol the difference is night and day,trust me. That's why i want to put everything off the car.

Going back to the point....delete the heater it hasn't been a good idea...here in Veneto fall and winter temperatures are low. This evening was 0°C and past week we had 10-15cm of snow.
Yes,there's a "device" insered into the cooling system and its function is to reduce the gas pression...i hope if it has air in it will can be bleed by the bleeding screw on the thermostat housing.
Tomorrow i'll try to bleed the system again,i hope i'll have good news.

[Brianmoooore]

Similar to here in the UK then, but LPG (propane) is much more common than CNG (methane).
I know from theory and experience that LPG gives no reduction in power, and has the potential for more power if you modify the car to make use of the higher octane value compared to petrol.
I can think of no theoretical reason, or find anything on line that suggests that CNG should result in a reduction in power either, so it seems likely that your CNG is simply faulty.
Park the car with the front a little higher than the rear if you can when you try to bleed it, and there's no reason why you can't bleed it at the CNG reducer connections in the same way as you would at the heater stub pipes.
You may get away with bleeding at the thermostat, but it's more likely to be successful at the pipes.
Does water come out of the bleed screw when you open it? The hole is very small, often blocks, and needs to be cleared with a strand of wire.

[DarioStraightSix]

LPG is more common here in Italy too. And,yes,lpg gives better performance. About mine there's another thing to say : the system have been installed in 1999. It's still an old generation type. The gas isn't injected but is "axpirated". There's a tube that is connected to the intake tube (the one that goes from the maf\air filter to the throttle body) and the gas goes in to the engine in this way. Probably i explained it in a terrible way...i hope you understand. I'll post you some pictures. Anyway,this old kind of gas system give low performance with both kind of gas. Methane gives the worst performance with both kind of systems.

Going back to the bleeding of the cooling system,thanks again for your help! Today i was too busy with my job,i hope to have the time Tomorrow.

[ethrty]

interesting, LPG is certianly a reduction in power in my experience (here in New Zealand), resulting in a decrease in fuel economy, however the far less price/litre offsets the higher economy, LPG results in a cost saving, providing that your milage is enough to offset the cost of install in the first place.

CNG is hopeless, and went out of fashion 20 years ago, and this is in a country that produces plenty of it, both geothermally and from "cowfarts"

[DarioStraightSix]

I've just did another bleeding of the system. I drove the car for 4-5 kms just to reach the operating temperature. When i stopped in front of my shop to check if everything works the same thing happened : temperature started to go up a bit and coolant into the expansion tank increased the level until it went out a bit from the cap....so i loosened the bleeding screw but only coolant went out...at this point i stopped the engine and i waited a bit to let it cool. The strange thing was that the hose from the thermostat to the lower side of the radiator was almost cold. I thought "bad thermostat?" But the radiator was hot...
Then,when engine was cold,i parked the car into my shop,it's a bit a tricky park to do so you've got to do some maneuvers and the car reached the operating temperature again. But this time no coolant boiling into the expansion tank,no super high level into it when i stopped the engine and the hose from thermostat to lower side of the radiator was warm.....it seem it works fine....
At this point i don't know very well what to think.....crazy thermostat? Maybe i ended the bleeding without having realized it?

[Brianmoooore]

Sounds like you may have got lucky and the manoeuvring might just have shifted the airlock. The last of the air will probably work its way out now, so keep an eye on both the level and the temp. gauge.
Red 325i touring in my pic. has covered about 100,000 miles (of its way over 200,000 total mileage) in my ownership running on an aspirated LPG system! The aspirated system pulls in air including fuel, while an injection system pulls in air plus fuel, so there is a minor reduction in power, but nothing that was ever noticeable in any way.

LPG is certianly a reduction in power in my experience (here in New Zealand), resulting in a decrease in fuel economy

The reduction is fuel economy is a myth, and in no way indicates a reduction in power! Not because it's not true that MPG reduces, but because of the way fuel quantities are measured at retail level, which is not indicative of their energy content. Fuel is more normally measured by weight, and if you apply this to cars, you will find that the miles per kilogram obtained from LPG comfortably exceeds that from a kilogram of petrol.

[DarioStraightSix]

Thanks for the answer Brian! So,at this point, the only thing to do should be drive a bit and see what happens...i hope i've been lucky.


About fuel economy on gas systems : the same engine have better km\l with petrol than lpg or methane (methane is the worst) but you save money because lpg and methane are cheaper than petrol. At least here in Italy people install gas systems for this reason,and for pollution restrictions on old cars.

[Brianmoooore]

Better km/l, but not better km/kg, which is the way fuel consumption should be measured (and bought), and is, in the case of fuel for ships, planes, etc., and in the wholesale market. The density of LPG is around 0.5, compared to around 0.7 for petrol.
The energy content of your petrol varies with its temperature - the higher the temperature of it when you buy it, the less energy you get for your money, or would do, if the pumps weren't temperature compensated to deal with this.
LPG's energy content varies much more widely with temperature than petrol, and since LPG is often stored in above ground tanks, there can be a considerable difference in its density between that on a frosty morning and at the end of a hot summer's day, and the dispensing pumps aren't normally compensated. I did some calculations once, and found the difference could equate to more than 1p/l.

[Funnybear]

I'm still going through issues very similar to this. (Without the LPG). Not tried the bulkhead bleed yet, but I've changed the thermostat, the viscious, The pump was changed no so long ago. Seems that everytime I drive it (Need to get to Cardiff and back on a regular basis. 400 miles most weekends) the temp still goes screwy.

If the bulkhead bleed doesn't clear it, I was going for a head gasket change. Got a feeling that the system gains air (Or exhaust gases) everytime I drive it, as I've tried to keep on top the bleeding just to 'clear' the system. But I never seem to get to the end of all the air as after each drive I'm still taking air out.

It's not a consistent thing either. The car can be fine sat on my drive, all up to temp, all bled out, warm air a'blowin. And then low and behold, a few miles down the road (generally around Gloucester. Must be the hills) I'll get into some slow traffic, the heater goes cold (with the temp sensor not going up too much to start with) and then that slow inexorable climb of that little white needle which is intrinsically linked to the leaden feeling in my stomach as it's dragged millimetre by agonising millimetre closer to the tarmac.

I hope it's not gone as far as a cracked head or warp-age. Don't think I could handle that. I just want the thing to work as it should. I've tried to look after her. Spent some money, wrenched a spanner or two in her direction. But she ain't happy and I just don't know how to fix her. If this was a woman, she would have been gone long ago.

Oh well. Bulkhead bleed it is next. Before I accept what inevitably is going to be the head gasket.

[Brianmoooore]

If the bulkhead bleed doesn't clear it, I was going for a head gasket change. Got a feeling that the system gains air (Or exhaust gases) everytime I drive it, as I've tried to keep on top the bleeding just to 'clear' the system. But I never seem to get to the end of all the air as after each drive I'm still taking air out.

Once all the air is out, it's out! If 'air' reappears, then as you say, it's gas from combustion.

and then that slow inexorable climb of that little white needle ...........I hope it's not gone as far as a cracked head or warp-age.

You won't get away with this very many times on a 2.5 M20 without cracking the head, even if it wasn't the initial problem.

[Funnybear]

Oooo. Don't say things like that. Suppose I just gotta keep going through the motions till it's cleared the fault.


I'll be asking for a new head from someone next.

[DarioStraightSix]

Brian,you was right!!! Today afternoon i went out for a little drive and everything worked well!!! Probably i bled out the last air in the system past Sunday.
It's awesome! Maybe i discovered its character only today because when i changed the timing belt i cleaned the rotor cap that was very very oxydated. Now the engine runs ways better,it reaches 6500 rpm without any hesitation like it did before.
Now i'm very very happy and proud to have done all the work by myself.
I thought that the E30 was an Amazing car before having one and now i've got the proof of it. E30 all the way!!!

And many many thanks again for the help!

Funnybear,have you fixed yours?