Hi,

 

My Mk2F (AAU) has recently had a new water pump, and new coolant "plastic heart".  I retained existing blue and black temp sensors as they were showing decent resistances.  I also retained my thermostat as it had been fine (VW genuine item, only done about 5000 miles).  New o-rings all round.  Coolant tests after the work showed no leaks, I got all the airlocks out, coolant level is stable and the bottom hose on the rad only goes warm at ~85 *C on the gauge when the thermostat opens.  Radiator fan also operates fine.  Car sits pretty at 90 *C on the coolant gauge running around town and along some b-roads. G12+ coolant was used at whatever the bottle says for dilution.

 

Last few days have been very cold outside, and I've had the Polo out on dual carriageways for the first time since the coolant work.  Once fully warmed up, and I get her up to 60-70 mph, the temp gauge drops to 80 *C after a couple of minutes, and settles just above 70 *C after, say, 5 min.

 

Years ago I had a thermostat jam full open and the temp gauge went to minimum in a minute or so of fast driving.  This is not what is happening now, it is very subtle, and I suspect either a very small opening in the thermostat even when "closed", or no problem.

 

Before I open her coolant system up and swap in a new stat.

 

i) Has anyone else had this happen?

 

ii)  Could my block just be getting aircooled by 70 mph wind in freezing conditions?

 

iii)  I have read the plastic hearts can be damaged.  My replacement one (gen VW off a donor engine) looked pristine (to me) after I'd cleaned it up.  Can a damaged heart cause a thermostat to leak past or fail open, is it obvious if there's damage in this region?

 

Cheers

 

noticed mine runs cool now its cold out ....took forever to reach 80 then sat at no more than 83 on the motorway

 

id be blaming the thermostat if you feel the gauge is accurate , mine is as im logging it on a aftermarket ecu

 

if i was running mine over winter i would block off the rad to help it

Edited 29 November, 20214 yr by steveo3002

Doesn't sound out of the ordinary bearing the weather at the moment in mind. As @steveo3002 says, it's probably worth blocking a part of the radiator off until the weather improves. I wouldn't do it on a more modern car, but I do on my old caddy van.b

Sounds like the cooling system is doing it’s job.Have you factored in using the cabin heater? 
 

When you switch it on and turn to ‘warm’ you are effectively increasing the cooling effect on the engine as heat is extracted from the heater matrix, which of course uses the coolant to provide the cabin heat.
 

My 1L takes forever to warm up in winter once the heater is put into use, it also runs cooler, to a point I start getting Mayo in the oil filler cap as the engine isn’t getting as warm. It’s absolutely fine and Mayo free in the summer.

 

Yeah I guess I'd better check the stat at some point.  I really should've tested it and maybe the sensor tip in a saucepan when I had things apart.

 

If yours is at 83*C that's pretty much bang on first opening temp.  My old VW one has 84 on the casing and online suppliers quote 84 too.  Haynes says 87 but I guess its splitting hairs over a few degrees.

 

I usually ride with the cabin heater at cold.... but I still get semi-warm air regardless so I think the proportioning valve must be a little out of whack.  Full hot is mega hot.  But even on "cold" if its dispensing semi hot air I guess it could knock things down by a few degrees.  I had her out for a run today and was getting 90*C to just under 80*C under mixed roads.  She warmed up in I guess 4 miles?

 

I (just about) remember in the 1980s people would cardboard their radiators.  And also use the cabin heater as an emergency heat dump if a car started overheating - usually in summer, baking the passengers even more but preserving the car's head.  Fun times!  

if  a stock rad can cope with spanish summer im pretty sure half covering one in winter would be fine , infact ive done it on mine when it was in more regular use  

Sorry, I just re-read my last post ending and it may have come across wrong, it's hard to tell on the internet - I meant that people had cardboarded their rads successfully in winter, and used the heater successfully as a dump in the summer.  Not that cardboarding had caused overheating which then required heater dumping.

Don't use cardboard, it'll go soggy and turn to pulp in the rad fins. Bit of plywood cut to size is the way to do it. My MK2 caddy's got it's radiator 50% covered and will have til spring. 

I use radiator reflector foam cut to size slid in front of the rad.

Lasts about 10 years before it breaks up..

 

Put the rest behind my house radiators to save energy of heat loss to outside walls which is its original purpose, not cars.

https://www.ebay.co.uk/itm/183796624376

 

 

 

Edited 1 December, 20214 yr by dvderlm

Nothing wrong with using that, anything which stops the airflow will work, but it might be a bit overkill. A car radiator doesn't radiate heat in the same way as a house radiator does because it's got airflow, which is more what you're trying to stop than radiation. 

No airflow queueing at roundabouts and junctions and traffic lights, which is what I do on commute, just as the thermostat opens after first 2 to 4 miles. 

Most of VW cars have good cooling system they get so hard to overheat, my firend on summer when he drive his temp is on 70 all the time i never see that car on 90DEG, on winter also, he has an Audi 1.9 TDI, and also vw have great cooling system thats hard to overheat, a lot of people tune vw and they dont have to upgrade cooling at all because of good cooling system, for example i have toyota 1987 and I upgrade with Solex carb and my car on red light overheat to the red line, but when im driving it than all is good and I have to upgrade my radiator with bigger one, so thats not a problem if u ask me, its winter and cold air from outside have effect on engine block and other parts.

So now temps are a little less Baltic I've had the car out a bit more and done some testing.

 

Thermostat (OEM) removed and checked in saucepan with thermometer: no gaps visible when closed, opens at 84*C right on the money.  A slight lag on fully closing (80*C), but I'm happy with this.

 

Black sender removed and tested by measuring resistance when dipping the sensor head only into water.

T/*C     Ohms

20         1280

50          406

66          252

74          200

81          177

86          130

 

Couldn't test higher temps as the saucepan steam hurt my fingers holding the meter probes but you get the idea.  A spare sensor from a scrappy was tested too and was within 10%, which gives me some confidence.  Google has a few charts but its hard to pin down specific VW models to get a manufacturer spec.

 

I was able to remove the black sender's connector and test resistance after a drive, I got 170 Ohm but the gauge was showing around 65*C, which disagrees with my measurements.  Also I had the gauge stuck on 70*C but the thermostat had opened as the bottom hose was warm.  Fan comes on at about 90 on the gauge.  

 

So I think its the gauge or maybe a bad connection somewhere else, instrument panel earth or voltage regulator fault.  The earth for the black sender's plug is good, I bleeped it out on the block.

 

I could bridge the sender's connector to check the gauge goes full swing, but am loathe to do this as I have previously blown a gauge with this method - it went all the way up then failed within about a second.

 

I could take the instrument panel out and check connections are clean, also the same for the gauge within the panel.   

 

Where is the instrument panel earthing point, is it on the firewall inside the cabin under the dash?

Any way to test the voltage reg inside the panel?

Anything that can be tested within the gauge itself?

Any other suggestions?

 

Cheers

 

 

That's from the 6N manual so your figures are not that far away 

Thanks Nige.

 

I had the instruments out today, there were no visibly damaged PCB components, no corrosion etc.  Likewise I looked inside the temp/fuel gauge but there's nothing really serviceable with the little wire coils and bendy metal strip.  Needles moved with light finger pressure so there's no mechanical jam.  No change in gauge behaviour.

 

I realised the Haynes diagram helpfully has pinout numbers so I will test the harness plug tomorrow with instruments removed, for earth and 12V feed.  I can probably test the temp sender to harness plug continuity if I bridge the sender plug, making it earth on both sides, then check for earth at the "sender's signal" harness connector pin.  Or loop a long wire from the sender plug into the cockpit and continuity test.  Hopefully this will prove the connecting wires.

 

Google says my voltage reg chip is 10V (ITT TCA 700Y).  If they fail, do they cause an open circuit (gauges dead), or do they just send unregulated alternator ~14V to the instruments (high gauges?).  Can they partially fail and give a lower voltage? 

 

 

 

Normally when the voltage stabiliser fails it results in no gauge movement 

does the gauge rise when the fan is on?  if it does move and indicate its getting warmer than "normal" id just leave it be , note where the new normal is and leave it at that   

Edited 3 February, 20224 yr by steveo3002

The gauge does still rise, but its been getting worse over the last couple of months/1000 miles.  My current normal gauge temp is 70 and fan cut-in is mid 80's.  I can live with it for the moment as you say.

 

Harness pins all checked out OK so I'm beginning to think the gauge itself is just getting to the end of its life.

You could try substituting the temp sensor for a 330ohm resistor and see what the gauge reads ?