Need a coolant flow diagram/explanation

[Northboundtrain]

I would like to know exactly the route(s) the coolant flows through my 1.6 n/a engine-radiator-heater core.  I believe it goes out the front port on the head and down to the water pump housing when the themostat is closed; and out the front port on the head, into the top of the radiator, out the bottom of the rad, into the water pump housing when the thermostat is open.  When the heat is turned on, I think it goes out the left (drivers side) port on the head, through the heater core, and down to the water pump housing.  This is all based on just what seems logical from looking at the cooling set up.  

Am I right, or can someone straighten me out?  Thanks.

[chrissev]

I would to know exactly the route(s) the coolant flows through my 1.6 n/a engine-radiator-heater core.  I believe it goes out the front port on the head and down to the water pump housing when the themostat is closed; and out the front port on the head, into the top of the radiator, out the bottom of the rad, into the water pump housing when the thermostat is open.  When the heat is turned on, I think it goes out the left (drivers side) port on the head, through the heater core, and down to the water pump housing.  This is all based on just what seems logical from looking at the cooling set up.  

Am I right, or can someone straighten me out?  Thanks.

You are mostly right.  It is a thermo syphon system assisted by the water pump, so the coolant flows up the way in the engine, and down the way outside of the engine.  Why do you ask?  If you are having problems with circulation, did you remember to pour the coolant into the top radiator hose and thence to the cylinder head, to avoid having air bubbles?  There is also a restrictor in the top coolant hose that gets plugged and causes circulation problems.

[racer_x]

Well, you're pretty close. The pump pushes water into the block. It goes up around the cylinders and into the head. There are two outlets on the head. Each outlet has a flange on it with one or more hoses connected to it. Pressurised, hot water is available at both flanges.

The one on the end of the head goes to the heater core. There's a valve in one of the heater lines that blocks this entire circuit when the heater is turned off. So with the heater/vent controls in the "cold" position (and assuming a working valve), no water flows through the heater or the heater return hose. Many gas cars also have a small hose loop  from the outlet on the end of the head for a coolant temperature switch or sensor.

The flange on the front side of the head has a big hose going to the radiator. There's also a big hose with the thermostat in it going back from the bottom of the radiator to the water pump. When the thermostat is open, a lot of water returns throug the radiator. But there are other hose(s) on the flange with the upper radiator hose. One goes down directly to the water pump. This is a bypass hose that allows the coolant to flow through the system when the thermostat is closed. There can also be another hose that supplies water to the water/oil heat exchanger (oil cooler, mostly). From the oil cooler, the water is returned to the coolant return pipe and hose (the one from the heater and expansion tank). All the turbodiesels, and all of the automatic transmission equipped normally asthmatic diesels had the water-oil heat exchanger. Some of the higher powered gas engines have them as well.

That leaves only the expansion tank to explain. The bottom of the expansion tank connects into the coolant return pipe (the one from the heater). The tank is there mostly to provide for the expansion and contraction of the coolant from temperature and pressure changes. The tank is pressurized (unlike most "overflow" reservoirs).

There's also a small pressurised hose from the top of the radiator over to the expansion tank. The purpose of that little is to burp any air out of the system. In theory, any air bubbles trapped in the system will eventually make it to there (the highest point on the radiator) and will be vented to the expansion tank. In theory, that should work pretty good. In practice, if you get air trapped in the block, it can lead to overheating problems.

But the quick answer to your question is that water flows out of the head and toward the water pump in all of the hoses attached to the head flanges. Only valves or thermostats will stop the flow of coolant in any given passage. The bypass hose from the upper radiator hose fitting on the head to the pump is the only line that is never blocked by design.

[Mark(The Miser)UK]

Well, you're pretty close. The . There's a valve in one of the heater lines that blocks this entire circuit when the heater is turned off. So with the heater/vent controls in the "cold" position (and assuming a working valve), no water flows through the heater or the heater return hose. n.

Well you're even closer  :twisted:
Except the above only applies to all Dashers Quantums Audi's
AND only a few Rabbits.
Most Rabbits have a permanant flow to the heater. Hot/Cold air is controlled by fart flaps. :shock:
 :mrgreen: Actually even the valve has a small groove in it for permanent bleeding.  Thank goodness I drive a real car! :mrgreen:

[fspGTD]

Most Rabbits have a permanant flow to the heater. Hot/Cold air is controlled by fart flaps.

Incorrect.  All Rabbits (which europeans know as MK1 Golfs) have heat controlled by a coolant flow valve.

[Mark(The Miser)UK]

Most Rabbits have a permanant flow to the heater. Hot/Cold air is controlled by fart flaps.

Incorrect.  All Rabbits (which europeans know as MK1 Golfs) have heat controlled by a coolant flow valve.

Well is his a genuine Mk1? or has it been contaminated with Mk2?

[chrissev]

There's also a big hose with the thermostat in it going back from the bottom of the radiator to the water pump.

actually the thermostat is in the water pump.

[Northboundtrain]

Thanks for the explanations.  I was wondering for a couple of reasons.  First, I recently installed a temperature sensor that feeds an analog guage.  The only place that seemed feasible for tapping into (it's a big sensor) was the upper radiator hose as close to the engine as possible.   I just wanted to make sure I was getting an accurate reading.  Also I may want to do an SVO conversion to this vehicle soon, so I'd like to know the best place to tap into.  I'm thinking the heater hose that comes off the drivers side end of the head so I get flow immediately upon startup.

Thanks again

[Mark(The Miser)UK]

Thanks for the explanations.  I was wondering for a couple of reasons.  First, I recently installed a temperature sensor that feeds an analog guage.  The only place that seemed feasible for tapping into (it's a big sensor) was the upper radiator hose as close to the engine as possible.   I just wanted to make sure I was getting an accurate reading.  Also I may want to do an SVO conversion to this vehicle soon, so I'd like to know the best place to tap into.  I'm thinking the heater hose that comes off the drivers side end of the head so I get flow immediately upon startup.

Thanks again

You want hot water to preheat the veggie?
The quickest pipe to heat is the heater pipe especially if it doesnt have that valve or its open.
 :twisted: In practice the top rad hose is used because it is convenient and gets warm due to convection. (thermostat prevents true circulation until engine warm enough)  :twisted:
 :idea: One technique is to take your upper hose off...  stuff it with sand and create a coil with copper microbore wrapped round it. Clean sand out and reconnect hose with your 'preheating coil'. Lag the outside. :idea: