Cooling fan manual and backup stat overrides

 A little enhancement on the main engine cooling fan control.

While the ECU fan management is rock solid it is at the mercy of input sensors.

It is straightforward to add a manual switch into the fan relay coil as an override. If my temp sensor ever goes bad again the switch under the dash will let me manually turn on the engine fan.

To make things more interesting I incorporated a tri-colour LED to show on the dash when the fan is on, it sits unobtrusively bottom right of the water temp gauge.

The circuit specifically designed for minimal changes to the main loom - just a piggy back on an existing cable and if my new circuit fails - for any reason - it should not disturb or otherwise upset the existing operation of the ECU to Fan relay circuit.

Off = fan is off

Green = fan on via ECU demand

Red (ish) = fan on via Manual dash switch demand (its actually red + green but the red is more intense)

Blue = fan on via Radiator stat demand

I have a VW Polo radiator with a mounting point for a simple temp sensor which closes a switch, and for me, grounds the cable when it hits a temp limit. This is the automatic backup if the ECU sensor fails again & will light blue on the dash as a warning.

 

Multiple demand on at the same time light green + the appropriate colour.

Circuit

The circuit itself on a Vero board mounted behind the dash with manual override switch beneath. The board is in one of the drier areas of the car but precautionary hot glue on cable ends and the board conformal coated to give it a chance in the relatively harsh environment.

All wire runs were subsequently given a second layer of insulation/soft fabric wrap too.

Emerald Pin 6

Emerald Confirmed that the ECU will not mind an external sink of pin 6 'Fan Relay control' to ground. The easiest place to tap into it on my car is near the ECU connector - a cable spliced on and suitably insulated.

These are all signal current circuits to the coil of the Fan relay - no significant current passing at any time.  Traced pin 6 to the orange wire - double checked by grounding it does turn on the fan - and spliced in my yellow feeder to the new circuit

Wrapped it all back up

That will do.

Loose ends

A few small changes to the cooling configuration and the final step in the engine rebuild to replace a dust cover.

1. Baffle to block the air gap between the radiator fan housing and the top of the radiator.

2. Coolant cap reduced from 20PSI to 16PSI

3. Reinstall the cam belt top cover which requires the aux belt and butterfly valve (or intake assembly) to be temporarily removed so it can slide into place from the front.

Subject to UK lockdown in Wales being relaxed, hopefully in the next month or so, we should be back to square one with a fully operational Zero!

A wash is all it needs now.

New coolant temp sensor

New parts arrived - a couple of thermostats at original 92ºC and 88ºC and ECU coolant temp sensor.

Standard 54mm/2" thermostat, drilled with a 4mm bypass hole to allow circulation before it opens - I thought I'd replace this anyway while the housing was open.

Confirming the failure point

Next up comparing the temp sensors, the new one is from Emerald however took a few minutes to double check before replacing. The part number is E450 on both, I think the 4011 and 0418 on the reverse must be manufacture dates - week number and year.

The old sensor read approx 9k ohms and the new one - in a similar room temp environment only 3k ohms. They drop resistance as temp rises so that would be consistent with the old one thinking the engine was colder than reality and therefore not turning on the radiator fan.

Double checked in the ECU software - the old sensor (left) thinks the ambient temp in the garage is 4ºC below and goes up to around 70ºC max. The new showing a much more sensible number - QED - sensor failure but within range so the ECU just wasn't turning on the radiator fan.

While I was here I checked no sensor connected - at which point the ECU reports 80ºC but also turns on the radiator fan.

Reassembly

A little fiddly to get the ECU sensor in under the dash one - requires removing both of them - but relatively straightforward.

Thermostat

I'm going to try a slightly lower thermostat value to let coolant into the radiator a little earlier at 88ºC which should let the radiator smooth the top of the warmup curve before the fan has to kick in 10ºC later. Should help things when the car is stationary and hopefully doesn't affect things significantly when moving airflow is present.

(Horizontal scale here doesn't mean anything - its just representative, Yellow where coolant is admitted to the radiator, and green the fan kicking in.)

Thermostat back in its home.

That was good - nice clear failure component identified, hopefully the new one lasts another 7 years.

Option/thought - there is a thermostat mounting point in my radiator - would just need a radiator mounted switch which grounds the lead on ECU Pin6 (or the other end of it on the fan relay).

Cooling system - maintenance

On the way back from Norway the car decided to chuck out all its coolant and peg the temp gauge at best part of 130ºC. After letting it cool and topping up the coolant everything was fine - but it was a particularly cold night coming back - so possibly just got away with it due to forward motion?

Today I let the car run at idle, part of its static monthly exercise, running up to full water temp and letting the oil circulate.... the coolant gauge again jumped up over max temp and on switch off blew the bulk of its coolant out of the overflow onto the garage floor.

Something then is still not right.

I wasn't really watching it so not sure if the radiator fan cut in when the engine was running.

Tests so far

Confirmed the ECU is seeing a temp reading - check

Used the ECU software to check the ECU could turn the radiator fan on - check

Swapped the fan relay with the aux panel one to confirm identical behaviour - check

Removed the thermostat and checked it opened around nominal 91ºC - check

Next up, monitor the ECU temp reading and see if its seeing the coolant temp rising and see if the fan relay keeps flipping - not sure if that is because the battery is low due to the car not running?

...

Update - sensor replaced issue fixed.

Spin-off

Nothing to do with the car itself.

A spin-off use for some left overs from the cooling system.

An off cut of silicone tubing, section cut out, makes a perfect sprung heat proof 'pot handle grabber' for the kitchen...

Polo radiator install completed

The Mk1 brackets left the radiator hoses a little low, bottom hose only just clearing the steering rack gaiter and top hose not quite right either.

Brackets

The adjustment I decided on was add some box section on top of the angle to lift the entire radiator up about 1". Majority of the weight should be borne by the original side brackets rather than directly through pop rivets.

I'm guessing the filled radiator weighs 6kg or so - hopefully the aluminium is up to the job of securing it while in motion.

The Polo radiator sits on top with its mounting lugs sitting in grommets in the tube. 

Fan sitting on the bottom tube and mounted to the rad tapped mounting points with cut down M6 bolts. With hindsight if I had mounted the fan on the bottom edge of the mounting tube, the top edge would have lined up with the  top of the radiator. I may need to add a baffle in there later so the fan airflow is all ducted through the matrix.

Pipes

I feel happier with the plumbing now:
    - Top tube kink/crank is just rotated to line up,
    - Bottom stainless tube shortened plus a 45º silicone reducer,
    - Radiator 8mm take off blanked off with some silicone pipe and a bung
    - Radiator middle/thermostat outlet blanked off with the bung that came with the rad

There is a slight bend in the, supposed straight, top radiator silicone connector - time will tell if that causes a problem.

Checked for leaks first with the 'patent air pressure kit' then filled with coolant and ran the engine up to temperature until the fan kicked in a couple of times.

All looks good. Happy with that.

Update - 100 mile ish test run around Kent varied driving, motorway, A roads - all seems stable so far.

Radiator brackets

Decided on the mounting for the new VW Polo rad. 

The bottom bracket made with aluminium angle sitting on the chassis radiator mounts. 

The radiator sits in it locating via pegs sitting in grommeted holes.

...and plates at the top which will be bolted to tapped radiator mounting points.

Fan offered up to check the nose clearance.

Update - modified this slightly to give better pipe routing and radiator position.

Plumbing

A picture of hoses to mull over. Top hose will be fine,. Bottom hose will hopefully re-use the existing stainless dog leg pipe, shortened, to get over the steering rack and meet up with the cold outlet currently closed off with blue masking tape.

Missing one radiator

Instead of repair or like for like replacement I am going to try a new 1983-1990 VW Polo Radiator. 

The core size is smaller than the GBS original at approx 380x323 but received knowledge indicates it will have enough cooling capacity. Readily available and at under £30 delivered (vs. approx £150 for the bespoke GBS one) the price is right if I ever need to replace it again. 

First step is coolant out and old radiator off. An 8 litre window-box perfect shape and size for the job.

Ready for the replacement...

  Top tube is fine,  just needs rotating,

  Bottom tube will need shortening and a 45º silicone connecting pipe,
  Brackets will have some aluminium and stainless extensions.

Good news and bad news - lights and leaks

New Headlamps

I fitted small 4" dominator headlamps which looked great - but 2 years down the line they have to go, just not large enough reflectors to generate good lighting even with higher power bulbs.

I didn't go back to full 7" lamps - but instead 5 3/4" with a full UK pattern lens. Picked them up  from CBS who are just down the road. Hopefully a good compromise between looks and function; certainly massively brighter even in daylight than the dominators.

Modified them to use the drilled mounting bolts from the old 7" lights means I can hide the wiring inside the mounting bracket. 

(Picture angle is deceptive - they are pointing straight ahead)

Leaks

Call it good luck that I decided to replace the lights and found the problem, or bad luck that I now have something else to fix :). The radiator looked a little beaten up, full of bugs, a few dints in the cooling fins etc.

The nose cone gave it away - why was it damp inside? and the gutter/bottom area of the rad fins full of coolant..

Started the engine up and when warm a little puff of steam from a hole... Its not a huge leak - the coolant height hasn't noticeably dropped since I was out a 2-3 weeks back.

Somehow a stone has gone in the back, unless this is the exit wound?

Looking more closely at the pic, very possibly damage from when the fan was originally mounted through the matrix. The picture shows bent fins, which are no problem but it appears the area they tore away from on the vertical matrix pipe has the pinhole leak. So that will be learning the hard way again.

It leaks hardly at all when cold, needs some investigation - repair or replace?  

Certainly needs fixing before Austria and I don't fancy bodging it this end of the season with radweld.