Heater bypass

[Littleeagle28]

1974 2002 automatic saloon.

 

I need to remove my heater for repair, and wish to continue to drive the car.

 

Is it possible to connect the inlet and outlet coolant ports from the engine block, using a hose to connect directly from one to the other, bypassing the heater?

 

Also, does anyone know the correct internal diameter for the hose, outside diameter is 28mm, thanks.

[Stevenc22]

Sure grab some heater hose and make a quick bypass loop.

[borgpj]

I wonder if a piece of Pex water pipe might be close enough to the right internal diameter?  Pex is semi flexible and could be bent into a "U", and clamped into the heater hose inlet and return lines.  It can certainly take the pressure and heat.

[calw]

I wouldn't try PEX.  A length of heater hose will cost a few pounds/dollars/euro from auto parts stores (sold from a large roll by the ft/m) and the clamps are already in hand.  PEX might function, but it's pretty stiff- so making the tight bend needed behind the engine might kink it badly, it's not designed for the vibration/firewall rubbing that will happen, and using the existing clamps may or may not clamp it to seal successfully.   Not worth the risk IMO

[2002#3]

Littleeagle28,

 

Here's a photo of a heater by-pass.  Look for the by-pass at about 5:00 from the fuel filter, almost touching the firewall, and, visually from this angle, under the carbs' linkage rod.  The by-pass goes away from the engine (sess visible), along the firewall, and back to the engine (more visible).  A plastic connector between the two hoses is held in place by two hose clamps.  One of the PO did that, I suppose.  By-pass can be achieved with a single hose with two bends if such can be found.  

 

FYI, a year ago I joined the BMWCC GB and affiliated with the Cornwall Region which I have visited many times.  BMWCC GB is a great group which has welcomed me profusely.  Am pleased to be a member of this illustrious organization.

 

Larry

 

[Littleeagle28]

Have just managed to buy a 1 metre length of heater hose locally, for £3.50 from advanced truck components, helpful bunch of people.

 

Will try and connect to both hose output/inputs on the engine block.

 

on another note note, what happens to the flow of coolant when the heater is switched to off, how internally does the coolant flow through the engine?

 

 

 

 

 

On another note

[M3M3M3]

alternatively, you can just plug/block off the heater inlet/outlet hoses at the head.  effectively same as closing the temp valve.  the cabin heater is not part of the engine cooling system flow.

[Stevenc22]

21 minutes ago, Littleeagle28 said:

Have just managed to buy a 1 metre length of heater hose locally, for £3.50 from advanced truck components, helpful bunch of people.

 

Will try and connect to both hose output/inputs on the engine block.

 

on another note note, what happens to the flow of coolant when the heater is switched to off, how internally does the coolant flow through the engine?

 

 

 

 

 

On another note

It has multiple flow paths besides the heater core loop

[jireland2002]

It is best to just plug the hoses at the pump and cylinder head.  If you don't too much flow will bypass the block.  Yes when the heater is on water bypasses the block but the heater valve is smaller than the hose ID and when you are using the heater it is probably rather cold outside.

[dlacey]

Although its likely not a problem this time of year, connecting the outlet and inlet on the block 'unrestricted' will 'short circuit' the radiator and can cause the car to overheat or run hotter. The water in that heater circuit is deliberately circulating a short loop through the head and through the pump only so that the heater works as early as possible on warm-up. In the summer, that water in the short circuit loop never goes to the radiator, so you can get a situation where the head is close to boiling and the rad is sitting at 70C. Blocking the outlet and inlet is same as having heater valve closed...  Here in Asia I don't like to have blocked pipe 'dead ends'  so I use a 'short circuit' pipe but I stuff a short length of small bore rubber pipe inside the short circuit hose to act a restrictor and force most of the water to take the radiator route. This works - can easily see the difference on the temp gauge.

 

9 hours ago, Littleeagle28 said:

Is it possible to connect the inlet and outlet coolant ports from the engine block,

Edited January 6, 2021 by dlacey

[jimk]

2 hours ago, jireland2002 said:

Yes when the heater is on water bypasses the block

Disagree with the statement.  Water is pumped first through that big square hole in the lower timing chain cover and into the block.  The flow pattern is then through the block around the cylinder walls and up through the water passage holes in the block deck and into the head.  From the head it depends on whether the heater valve is open or not that all the flow leaves the head through the water neck.

As @dlacey said, install a restrictor in the bypass hose if the heater is bypassed because the bypass water has not been cooled as would be if the heater valve was open.