I had to replace the radiator and waterpump in my 1984 380SE. I have now filled it up with coolant.

I notice that the heater is not blowing hot air any more. My guess is that the cooling system and heater core have air trapped inside.

How do I bleed the system ?

Thanks,

Amit

Amit:
When I did a coolant flush on my 97 C230 last week I drained the coolant from the radiator via the valve at the bottom of the radiator, and drained the coolant from the engine block via a special drain bolt on pax side of hte engine.. draining was done with engine warm and the heater "on"..

Replacement of the coolant > closed all valves > added coolant > squeezed the hoses to force coolant through the system.. and kept adding coolant till it would not accept anymore > started engine got it up to operating temp... system seemed to push air out of the system..

heater on >> it has heat..

When I replaced the coolant, Ieven kept the top radiator hose disconnected in order to give the air an easy path to escape.

I think the radiator side has no air. But the heater core side probably does.

According to the service manual for my 380SE (actually, the manual covers various years of the 116 engine from 1981), which I was just browsing at lunchtime (planning a coolant change before winter storage) you need to set the climate control to DEF position (maximum 'on') during the coolant change process.
Also, and I haven't yet verified this by actually looking under the hood, there may be a bleed screw of some sort right above the water pump that is supposed to be opened during refill to allow air to escape....Anyone who is familiar with the 116 engine cooling system can verify this?

Added: I checked under the hood at supper, and there is a hose, not a valve/bleed screw, leading into a T fitting in the hose from the upper radiator tank to the expansion tank, which, according to my manual, replaced this bleed valve in 1981 on the 116 engine. Maybe someone else can offer a method to bleed the airlock from your heater exchanger, where I'm thinking it is...

__________________
1986 560SL
2002 Toyota Camry
1993 Lexus

I took Friday off work and put the ol girl into the garage for the dreaded coolant change, which I was going to put off until spring but decided that a 4 month winter storage would be better with a system full of Zerex G-05 than green Prestone. You guys on this forum convinced me to change it BTW.

Problem #1 was the radiator not being centered over the drain plug opening, probably due to the aftermarket A/C condenser being a little wider than the OEM. That was fixed by cutting out enough metal and rubber around the drain plug to allow it to come out. Miraculously, the hex-head plugs in the block screwed right out, so I was able to drain block and rad.

I previously ran the engine for about 5 minutes with the auto climate temperature dial up to full heat and the defrost button 'in' (as the manual specifies). I noticed that I only got about 10 litres instead of the 12 that the system is supposed to hold, but it was up to the mark on the tank, so I didn't worry too much.

Next, I closed the plugs and filled up with a solution of Prestone flush and water. Here is where the trouble started. No way was I going to pull the thermostat to do this job, since it shouldn't be necessary (?) and I had no fresh gasket anyway. But because the temperature here is hovering around freezing (0 - +7deg celcius), the inside temp guage wouldn't pass the 80degree mark, and since the thermostat opens at around 84degrees (from my manual), I wasn't sure if anything went through the top part of the radiator or not.

After almost a hour of trying to coax the temp up (rev engine, idle, rev, idle), I quit and drained the flush solution out (about 6 - 8 litres), refilled with very warm water from the bathtub (to save time, waiting for cool down), then drained again. I then mixed up my Zerex and water (50/50), and refilled, again with climate controls on full hot. This time I got about 8 litres in before the tank overflowed. Squeezing the upper hose while filling seemed to help.

I then went for a 10 minute drive, returned, and it took another 3 litres. Since then, even driving around doing errands in town, the guage never went far past the 80 degree mark. I guess I'll wait for warmer weather next spring to put in the other litre. I figure air doesn't freeze and crack blocks/radiators anyway, right?

Well, if you've read this to here, I'll note that at no time did I ever have any problem getting lots of heat from the climate control, so I'm not sure why you aren't, and the airlock theory may not be correct, but I really don't know at this point. One thing for sure: this is a long, messy, frustrating job that I would do again in 2 years but only in the summer!

Also, I think I'm correct in that the system fills from the bottom of the radiator (into the lower tank) up, forcing air to the top as it goes. But, if the thermostat is closed, the coolant would also go up the lower hose to the pump and then into the block and heater core (if the climate controls were all open/on full), again forcing air to the top and eventually out the little hose from the top of the water pump.

The thermostat closed would not allow any coolant into the upper part of the radiator, beyond the highest point in the engine, before it would backflow into the tank and overflow, but maybe it would also restrict passage of entrapped air from the block and heater core too.

__________________
1986 560SL
2002 Toyota Camry
1993 Lexus