PD Tdi overheat and plumbing Q's

[zak]

Overheated yesterday towards the end of an otherwise happy 2 hour run. I noticed the temp gauge go high and by the time I stopped the bottle cap was whistling like a kettle. The Bottle was empty but under a lot of steam pressure, I think the bottle is distorted now. The cap is not that old and a good one from BW. I let her cool down a bit and refilled but was unable to get air or water out the rad bleed with the front wheels parked up a slightly steep hill. The rad felt cool. Worryingly it wouldn't run when I first tried to start, would start but soon stall. Hope that wasn't close to seizing ? It got me home OK. The coolant has always felt a pain to bleed and never felt like I'd got the air out. I often wonder if I should add a bleed point in the engine bay, but where.
I had recently noticed a regular drip from the new BW SS rad pipes where they join engine bay, but I'd tightened the jubilee but was still leaking. I plan to fit a Norma or T clip hose to hopefully seal. The Bottle had coolant in before I left but guess air had got in the system.
Its' recently been in for some work with a good T25 tech and he felt that maybe the plumbing wasn't quite right and that perhaps the thermostat was staying open. On the back of the PD block is a small outlet and on mine its capped off, I'm guessing it should go to a header/coolant tank but I probably have the wrong bottle for that?

At no point have I heard the fan run but I just shorted across the rad temp plug and the fan runs on both speeds.

My gauge/red light has never been right since conversion, needle reads high and I just have to adjust resister inline to sort that one again. The red light is another story, sometimes its on all the time but if I stop after a short run seems to behave as it should.

Any suggestions welcome please?

[zak]

So I'm thinking it runs like this,



Maybe thats just fine?

The small outlet on the back of the block is capped with a silicone cap.

[silverbullet]

I know almost nothing about PD engines but...all VW inlines must have basically the same coolant flow direction?
I would "go cheap early" and test the thermostat first, since a cold radiator suggests that it isnt opening. If the heater is still working i.e. really hot when set to full heat, then it may help to confirm since that's on the bypass circuit and should always flow water.
A new or recent 'stat doesn't mean that it can't have failed shut after a short time.
If it had failed open, the engine would just take a long time to warm up.
All of which assumes that it's plumbed in correctly.

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[syncroandy]

The fact its been running for some considerable time since the conversion until you had this problem suggests whatever happened is more likely due to a fault (eg. leak) than a 'design' issue ?

Having said that I do recollect scratching my head a bit when a looked at the later I4 coolant systems a couple of years ago. IIRC the donors have an 'always-on' heater matrix, unlike the T3 which is valved. This needs to be properly taken account of in the plumbing design.

[zak]

Thanks Ian, yes the heater kicks out hot air. When first driving I can see the gauge rise high then drop down a little as the stat opens and then steadies.

Its done a good few thousand miles like this but I'm not really confident its plumbed right. Also not sure that bottle is right, as I understand it the Tdi normally uses the round bottle with one large outlet at bottom and a small one at top. Mine seems to have a lot more plumbed in the top.

First thing will get a stronger hose clamp to try and stop the SS hose drip, I'm guessing thats where the air got in !!?

Can anyone recommend a tool to assist bleeding please?

[zak]

The fact its been running for some considerable time since the conversion until you had this problem suggests whatever happened is more likely due to a fault (eg. leak) than a 'design' issue ?

This is true Andy, I'm guessing the drip is the culprit although it was just a wee steady drip and there was a lot of air in there when she overheated. Picked up a few heavy duty clips today, I'll put them on tomorrow (weather permitting ) and hopefully that will stop it. Still think that the thermostat might be staying open.

I'll need to replace the bottle as I think its distorted now. I was hoping some Tdi guru would be around to suggest a way forward.

[syncroandy]

The coolant circuit on the 1st gen TDI's is the same as the T3 I4 factory-fitted engines, so the coolant plumbing is a no-brainer.
The 2nd gen TDI and the PD have a different coolant circuit design so have to be re-done from scratch when swapping the engine. As I've not done one myself (yet), I'm unable to make any specific suggestions.

E D I T: OK, so I thought I'd try and help by checking the docs on PD cooling, and it's doing my head in already ! The diagram in the workshop manual clearly shows the direction of flow with arrows. It shows the flow 'in' to the thermostat housing, toward the bottom of the engine, and the flow 'out' near the top of the engine (on the back of the head). Fine.

*But*, it says the flow 'out' of the engine goes to the *top* of the rad, and the flow 'in' to the bottom of the rad, this seems the wrong way round to me. Surely to help purge air out of the rad the flow into the rad should be the lower one ? Anyone got a clue how this is supposed to work ?

Also, I can see there's a 'lower coolant pipe' which seems to be a bypass taking coolant from the heater circuit and putting it back in next to the thermostat to open it as required. In a T3, I think it's important this flow is maintained *even if the heater valve is closed*, otherwise the thermostat may not open. The Subaru circuit is the same in this regard.

[zak]

The diagram in the workshop manual clearly shows the direction of flow with arrows.

Is that the same diagram I posted above Andy ?

E D I T Think I found the one you are looking at, very helpful, thanks Andy (although now its doing my head in !!)

[silverbullet]

The coolant circuit on the 1st gen TDI's is the same as the T3 I4 factory-fitted engines, so the coolant plumbing is a no-brainer.
The 2nd gen TDI and the PD have a different coolant circuit design so have to be re-done from scratch when swapping the engine. As I've not done one myself (yet), I'm unable to make any specific suggestions.

E D I T: OK, so I thought I'd try and help by checking the docs on PD cooling, and it's doing my head in already ! The diagram in the workshop manual clearly shows the direction of flow with arrows. It shows the flow 'in' to the thermostat housing, toward the bottom of the engine, and the flow 'out' near the top of the engine (on the back of the head). Fine.

*But*, it says the flow 'out' of the engine goes to the *top* of the rad, and the flow 'in' to the bottom of the rad, this seems the wrong way round to me. Surely to help purge air out of the rad the flow into the rad should be the lower one ? Anyone got a clue how this is supposed to work ?

Also, I can see there's a 'lower coolant pipe' which seems to be a bypass taking coolant from the heater circuit and putting it back in next to the thermostat to open it as required. In a T3, I think it's important this flow is maintained *even if the heater valve is closed*, otherwise the thermostat may not open. The Subaru circuit is the same in this regard.

Some coolant systems appear to have counter-intuitive flow directions, but putting hot in the top of the radiator and getting cold out the bottom means that there is also some thermo-siphon effect when the engine is shut down.
The fact that the later hvac systems (like the advanced-for-its-time Subaru) are full-flow and mix hot & cold air vs the T3 being a restricted flow bypass-fed heater is an important one.
Shut the heater valve on a badly-plumbed later engine and you can get all sorts of restricted or even reverse flow problems that can upset ecu temp sensors and all sorts...

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[zak]

This is a lot easier to follow than the diagram I had.

[zak]

So this is what I have (drawn in a similar way to the above workshop manual pic).

As Andy says the van has done quite a few miles with this plumbing so it IS working and I’m not saying its wrong but as I may need to change the header bottle I wonder if it could be tweaked.

Looking at my sketch I seem to have a lot of flow through the expansion bottle, is that OK?
And re the Oil cooler, I’d have thought water will take the path of least resistance and again looking at the sketch there is a parallel path to the oil cooler one into the top of the expansion bottle. Am I getting the best flow I could through the oil cooler?
And also VW cast that small rear outlet in the head for good reason but on mine its capped. From the VW manual diagram that usually goes to the top of the expansion bottle. (However this engine is at 50 degrees so maybe its not the highest point anymore)

I know I’m in danger of making a mountain out of a molehill here but I note that the manufacturer of the conversion kit that I have (US based FAS) uses the round bottle with just the small inlet in the top so their plumbing is definitely different.

[silverbullet]

My old (early) Subaru conversion was plumbed in so that the expansion tank had through-flow, I don't know if it helped or hindered matters but it was never right because of the aforementioned heater issues.

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[zak]

The slightly rusty jubilees were not sealing at all well on the recent stainless water pipes so hopefully that was the cause, gone overboard and replaced them with fancy Mikalor clips. So grateful for your valued help chaps but in the absence of a Tdi plumber guru gonna put it back as it was for now, not really confident its right but fingers crossed. Still surprised my water bottle blew up, see the pic, they look like me before and after an eating and drinking binge session.

[937carrera]

Mikalor clips, you won't have any problems with those, they're great

[zak]

So all back together as it was but without the pipe leaks. Fixed the temp gauge position with a variable resistor (for now) and the false flashing red light issue seems to have gone away.

After a good run and bleed all seems well but looking at things in more detail both ‘in’ and ‘out’ pipes to my stock built-in PD engine oil cooler seemed very hot (on a fairly cool day)

Can anyone give an opinion on the below please?

Looking at the factory diagrams again compared to my pencil one (Both above), as I understand it -

1. On factory diagram the ‘out’ from the oil cooler feeds straight into return behind thermostat housing giving prompt oil cooler temperature feedback to the thermostat. (I.e please open I’m hot etc.)

On my setup the oil cooler ‘out’ goes off to the top of the header bottle. Slower feedback loop to thermostat?

2. On the factory diagram the small pipe (about 8mm and hence restricted flow) in the back of engine in cylinder head goes to the top of header tank. (And also into large flow out to radiator)

On mine that small outlet is capped off (possibly because engine at 50 degrees ?) and I have a larger pipe (about 19mm) Tee'd from large pipe out to radiator. This also goes into top of header tank and merges with oil cooler ‘out’ coolant and on into the pipe that I imagine should trigger thermostat opening/closing.

I’m out of my depth here but with my limited knowledge it looks to me that the stock setup mainly has flow (bigger pipe) from the oil cooler ‘out’ to trigger the thermostat open.

On my connections the oil cooler ‘out’ goes through the header tank and also mixes with the rad out feed through the header tank before getting back to the thermostat. Seems a slower temp feedback loop, does this matter ? Have I made a mountain out of a molehill yet !!