engine and drivetrain Heater hose routing

[Guest Anonymous]

Talked about routing the hose for the heater exiting the back of the head to a "tee" in the upper heater hose by passing the heater. I finally spent the 2 hours and $20 worth of parts to do it. Works great! The heater hose I used has a 0.75 inside diameter and routs directly to the copper "tee" I installed in the upper radiator hose. The hose is the same temperature as the hose coming from the front of the head.

Unfortunately BMW has had head problems with several of their older models and it has been traced to lack of coolant flow reaching the back of the heads. The flow just dead ends. The solution, as only a BMW engineer living in northern Europe would select, was to have a return to the radiator go through the heater from a port in the back of the head and return to the radiator thus getting rid of the dead end. Maybe you always have your heater on in Germany but not in San Diego! Cracked heads and deteriorated head gaskets are the main problems. On 2002 engines it is cracking of the head between the 3rd and 4th cylinders. My 1602 head failed with a crack between3&4 cylinders with my 3.5L big six in my 735IL the head gasket failed around 5&6 cylinders. The 2002 heads are quite tough and can withstand a long time before they fail but with time a weld up or a new head is in order.

If you have dual side drafts and your heater sucks it may be because the return from your heater with the side drafts goes to the water pump and not to the radiator as it was originally designed to do with the single down draft Solex carbs after it heated up the bottom of the carb.

After 41 years with these cars still having fun.

[c.d.iesel]

how many miles were on your 735 ?

how often was the coolent changed in both cars ?

[Mike Self]

I have one. Came off a running engine about 15 years ago and has been lurking in my attic ever since.

mike

[eurotrash]

Anyone have photos here??

[TobyB]

Huh.

If you look at the new style heater valve, even in the 'full off' position it's

set to bypass a tiny bit of... well, probably air. And maybe coolant, but not

enough to really transfer much heat.

If the back of the head's completely blocked, I could certainly see it keeping

a pocket of air in there, and that'll let the head develop a hot spot,

with all the attendant problems.

I kept the heater hose routing, but put a plug with a small hole in as an

air bleed. If you just bypass it, it's enough hot water bypassing the radiator

to make a significant difference in marginal cooling situations

(racing at Spokane, for example)

with the bypass hose mostly plugged, I've never had a problem back there.

On an M10, that is.

What I've found,

t

[jimk]

If you have dual side drafts and your heater sucks it may be because the return from your heater with the side drafts goes to the water pump and not to the radiator as it was originally designed to do with the single down draft Solex carbs after it heated up the bottom of the carb.

I disagree with your explanation of the water flow direction for the single barrel solex carbs. The water does not flow towards the head outlet fitting from the intake water jacket, it flows from the head outlet to the intake water jacket, then out the bottom of the water jacket of the manifold to the suction side of the pump. That short hose provides heat continuously to the intake whether the heater valve is open or not.

Not to say the heater wouldn't provide heat if hooked up to the head outlet fitting

[Guest Anonymous]

The 735 IL lost the head gasket at 192,000 miles. (225,000 now)

[Guest Anonymous]

When I put on my side drafts (November 1987) I had to get rid of the mechanical fuel pump and I had to literally saw off the hose connection on the back of the twin branch water housing and use JB weld to close it. This was due to the intake manifold used on the side drafts taking up this location. I eventually found a 320I water housing that lacked the rear hose connection.

If you have the Haynes 1602 & 2002 manual a good picture is in chapter 2 picture 1.4b. It shows the mechanical fuel pump and the hose connecting to the back of the water housing. That hose is the line originating from the heater then going to the manifold that finally goes into the water housing on its way to the top hose to the radiator. The large hose that comes into the picture from the passenger side is a bypass hose. The hot coolant from the head enters the water housing at the flanged connection and then heads to the top radiator hose.

The original side-draft installation instructions changed this routing and directed the heater hose to be attached to the water pump with a 1" hose using a reducer to match the 5/8" heater hose.