Fully understanding cooling system

[Cobalt_drill_bit 7]

Dear people,

 

First off I would like to say that I like this forum. Nice people who want to share their knowledge about the 205. But I’m a naughty person because I don’t have a GTi myself. Still I seem welcome. However I’m going to add some GTi parts to my TU1M 205.

 

Alright, I’m going to plan an extensive cooling system flush in the Deutsche Gründlichkeit style. Can’t hurt this French car, does it ;-)? I’ve no experience in doing a cooling system flush or even a refill. But I think with my careful planning and asking for an experienced hobby mechanic at the DIY repair shop to assist in the bleeding process I think it will work.

 

Ok, part of the planning process is to map the cooling circuit I have in my car. I consulted the cooling system related servicebox pages and connected the dots to make a block diagram of it. As the servicebox doesn’t give complete information of the cooling system I’ve added some assumptions (like the direction of flow) in order to show you my best guess as to how it works. I’d be grateful if you can correct me in some areas.

 

 

Although this block diagram is an abstraction, the blocks are positioned in their relative locations in the engine bay. As if you're standing in front of the car. But I think most of you already got that :-)

 

Regarding the hose diameters, I went to the salvage yard, found a 205 with seemingly identical cooling system hoses. Pulled them out an measured them with a digital caliper at home. I've done this in order to buy the correct diameter transparent hoses for the flush setup.

 

This might be a nice one for the article section. I hope some members are willing to comment on this to verify, add and correct some stuff. I will then correct it and make an article of it.

 

Questions:

 

1a) I'm a bit unsure about the direction of flow in the Heater water outlet hose around the intake manifold. I've also assumed for a coolant passageway through the intake manifold gasket. I couldn't believe the intake manifold is heated just by this little hose without a complete circulation circuit. So, the presence of coolant passageway through the intake manifold gasket is very likely. Can anyone confirm this? Maybe there is even a book of my engine to explain that. If you know, please tell me.

1b) Then the direction of flow. The water pump sucks fluid through the thinner port does it? When the engine is cold the thermostat prevents circulation through the big radiator hoses as well as the heater water inlet hose I assume. So the only circulation that happens is the heating of the intake manifold. But is the direction of flow correct here? I think this would make most sense because the other way round would mean that when engine is hot the intake manifold heating is compromised due to the cooled down water it gets from the heater core.

1c) Because there is nothing that would prevent circulation in the intake manifold bypass circuit. The water pump will go on right on when the engine starts right? But if you block off circulation there you will ruin the water pump I suppose. This one is just for my understanding.

2) Ok, the cabin air temperature control knob (rightmost) sets the heater control valve position, right? I couldn't find the heater control valve in the servicebox pages. Where should I put this?

3) The thermostat will open or close both output ports at the same time does it? When open the circulation through the radiator will go on anyway and circulation through the heater is controlled by the heater control valve does it?

4) Haynes talks about an engine water drain plug (page 36 of the PDF version) I could only find an M6 drain screw on the engine water output tank assembly. Is that supposed to be the drain plug? If not, what does loosening this M6 bolt do? And what is the drain plug then?

5) When the engine is hot and circulation through the radiator is going on. The driving wind is used to cool the coolant in the radiator. If that isn't sufficient (still too hot) some system is turning the radiator fan on. Which system?

6) Am I missing some component of this cooling system? Is it true that there is only one bleed screw, or should the M6 drain screw on the engine also be considered a bleed screw?

 

Well turns out to be a large posting. Maybe my style of explaining my assumptions and asking for confirmation might irritate some readers. Look, I'm not doing this to show off my knowledge or are a type of guy who is in need for approval. I do this purely to enhance communication because I think this is the easiest way for you to spot where I might be off in my thoughts about the cooling system.

 

I have to say I'm curious about your comments on this.

 

Best regards,

Maarten Verhage

 

[Tom Fenton 1,524]

Very thorough, I can’t help think you are overthinking it a bit, pull the main rad hoses off and flush with a hose pipe in both directions is usually more than adequate. If you are really keen do the same to the heater matrix but don’t be surprised if it springs a leak not long afterwards.

There is no heater (water) control valve, the matrix recieves a constant flow of water and the various flaps in the heater box control how much air passes through the matrix (or none).

[Cobalt_drill_bit 7]

Hi Tom,

 

You know, I'm a type of guy who cannot deal with just repair or maintenance guidelines like the procedures in the Haynes manual. I have to understand the function of the stuff I'm dealing with. If I understand it, I can make the correct decisions during the repair when something doesn't go as planned. I hope you can respect my approach.

 

I decided to buy the book: "Rta 112.1 Peugeot 205 Essence et Diesel" to find more detailed info regarding this. Also I will again go to the salvage yard. Unbolt the thermostat housing of a similar 205 and see which channels are open in the hot and cold conditions.

 

I would be still nice if someone who has answers to my questions is willing to spend some time on it to share their knowledge with everyone here.

 

Regards, Maarten

[trogboy 17]

Hi Maarten,

 

Since you have made the effort of posting I'll try and answer your other questions not covered by Tom.

 

1a) Yes the manifold mating face has two waterways that match up to those in the head - a small portion of the water comes from the pump, via the water jacket round the pistons, via the head, the intake manifold and via the small pipe to connect into the heater matrix return line to the pump.

1b) Yes, however the output from the thermostat housing (you call it a hot engine water output) to the heater matrix is not governed by the thermostat - it flows all of the time that the engine is running.  

2) No heater control valve as per Tom's answer.

3) No.  As per answer 1b) the thermostat only controls flow into the large diameter hose to the top of the radiator.  When open flow will continue through principally the heater matrix and through the radiator.  Assuming sufficient cooling the system self regulates by the thermostat alone.

4) The engine water drain screw that you've noted is really a bleed screw to allow air out when the thermostat is closed when filling the system.  IIRC the engine bleed screw is located in the front face of the block below and to the right of the exhaust manifold and taps into the water jacket around the wet liners for the pistons.  It's been a few years since I've played with  TU engine but it is a hex headed set screw and something like 16 or 17 mm across the flats.

5) There is a thermoswitch in the radiator which triggers the electric fan.

6) See answer to 4).

 

Hope that helps,

 

Adam 

[Cobalt_drill_bit 7]

Hi Adam,

 

Thanks a lot for your time and effort answering all my questions. Based on this I made a update of the block diagram that will take all of this into account.

 

 

Corrections and suggestions for improvement are welcome. I hope this will benefit TU engine owners.

 

Best regards,

Maarten Verhage