Volkswagen Passat Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter #1
My B5.5 1.8t is slowly losing coolant and I'm having a hard time locating the source.

The plastic heater core and tubing seem a common culprit and while there are no clear visible signs of leaking, I want to temporarily disconnect the core to either identify or rule it out as the problem.

The online consensus seems to be that it's better to bypass the core by looping the input/output hoses at the firewall, instead of disconnecting and closing them both off.

AFAIK there is constant flow through the heater core on these engines, even when the heater is off. Hence, the argument goes, flow should not be impeded or excess pressure might damage the circuit.

However, the hose connection diagram shows the coolant coming from the engine also passing through the oil cooler. If I bypass the core, that would lower the impedance of the heater path. In effect, I could imagine a reduction of circulation through the oil cooler, possibly increasing the chance of overheating? Should we block rather than bypass instead?

I'm not sure about the coolant pathways inside the engine and so I struggle to understand the actual consequences of either approach. Online discussions tend to lack sufficient detail.

Who understands the construction of the 1.8t enough to answer this definitively?

18t Coolant hose diagram.jpg
 

·
Registered
Joined
·
1,204 Posts
Bypass. Our Passat's have the heater core continuously circulating the coolant. Heat for the cabin comes by activation of the blend door to send heat where you want it.

Slide the two hoses off, join them with a pipe of appropriate OD and re-attach the clamps.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #3
Bypass. Our Passat's have the heater core continuously circulating the coolant. Heat for the cabin comes by activation of the blend door to send heat where you want it.

Slide the two hoses off, join them with a pipe of appropriate OD and re-attach the clamps.
Sure, but that doesn't answer my question regarding the possible negative effect on flow through the oil cooler or other things.
 

·
Registered
Joined
·
926 Posts
We've heard from owners who've bypassed the heater core, and never heard of an issue with oil temp (or anything else, other than no cabin heat).
We've never from an owner who blocked the hoses.
I'd bypass the core. YMMV.
 

·
Registered
Joined
·
26,585 Posts
It should not make a difference either way. The coolant flow to the oil cooler may increase slightly if the lines are blocked, but the coolant would just circulate a little faster. Most of the coolant still runs right back into the engine behind the thermostat opening and recirculates until the thermostat opens.
 

·
Registered
Joined
·
319 Posts
I bypassed my heater core two days ago due to a leaking in the inlet pipe, possible a crack on it, must be very small and not visible but it is there. I will reinforce the two pipes in the inside with 5/8 copper pipes with some JB weld following the appropriate write-up as soon as I receive the copper pipes. What I noticed after bypassing the heater core is that the pressure increased noticeable in the cooling system and it will get rid of the coolant in the expansion tank if it is left above the minimum line so for now I keep the coolant level at the minimum other than that no problem. This leaking started after replacing my thermostat and filling up with G-12 50/50 ratio with distilled water, before this I was using G-12 100% which make wonder if using it 100% help to keep the system from over-pressuring. I know the manufacturer recommend the 50/50 coolant/water ratio but will use it maybe 80/20 ratio or 100% instead which may help against pressure in excess. Thoughts and words of wisdom are appreciated.
 

·
Registered
Joined
·
8,940 Posts
The heater core should only be bypassed (NOT blocked), blocking it would greatly reduce the coolant flow through the engine while the thermostat is closed.
This could delay the thermostat opening, and cause damage due to overheating in the engine before the thermostat opens.

Passatfan2
100% coolant doesn't transfer heat well, and should be used at 50/50 ratio, you can safely go a little stronger in extreme cold conditions.

Have you checked for exhaust gasses in the coolant ? You might have a cracked head or leaking gasket, caused by overheating.
 

·
Registered
Joined
·
290 Posts
My local Autozone sells a flushing T for a dollar. You have to ask about them because they are behind the counter. That is the easiest & the quickest cure, Remove the 2 hoses and use the T to join them. You can even remove the cap to help bleed the system.
 

·
Registered
Joined
·
319 Posts
The heater core should only be bypassed (NOT blocked), blocking it would greatly reduce the coolant flow through the engine while the thermostat is closed.
This could delay the thermostat opening, and cause damage due to overheating in the engine before the thermostat opens.

Passatfan2
100% coolant doesn't transfer heat well, and should be used at 50/50 ratio, you can safely go a little stronger in extreme cold conditions.

Have you checked for exhaust gasses in the coolant ? You might have a cracked head or leaking gasket, caused by overheating.
Thank you Tom, it make sense. Hopefully the only leaking i have is the one I am dealing with right now.
 

·
Registered
Joined
·
41 Posts
Contrary to what would seem to make sense, turning on the air conditioner and recirc will actually dehumidify the interior, helping to defog the inside of the windows. Just don't have it set on defrost.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #11
Contrary to what would seem to make sense, turning on the air conditioner and recirc will actually dehumidify the interior, helping to defog the inside of the windows. Just don't have it set on defrost.
Sure, but that's unrelated to the topic at hand.
 
1 - 11 of 11 Posts
Top