low temp thermostat

[sambb]

If the car is hitting mid 90's just tootling along in traffic not even getting on boost on the way to work and hitting the odd traffic snarl here and there then what I'm describing is going to be pushing things a bit beyond that. That's an assumption yeah but some things just stand to reason don't they. I can't log when I do runs but I have seen a lot of the coolant temps on the road when I was keeping an eye on inlet temps. But next time i'll plug in when I get back to the pits to see what the temps are doing for sure.

I've gotta say I'm struggling with the concept of coolant temp not rising after you shut it down. Coolant temp will rise when you hit a traffic jam. Your water pump isn't pushing hard, everything heatsoaks, yeah fans will switch in and out but over time the temp creeps up. That's why everyone overheats in traffic. When you shut a car down hot to my mind that's got to be worse for the period immediately after. The fans may run for a bit but even if the thermostat is open there's nothing to push that briefly fan cooled water through the engine for any decent period. The rest sits in the head/block. The water instinctively wants to cool but the engines thermal inertia is on the way up, not down. dunno. For my engines sake I'm happy to be proven wrong on that one.
Like you say there are a range of things that can be done if you're worried and have to do a stationary cool down. They are saying its going to be 30 degrees tomorrow. If I have some spare time before I arrive at work I think i'll have to plug in, hammer it and then park it up hot and see what the temps do.

[Martin]

How would the fans kick in after you park up if the water wasn't getting hotter?

It's not that the water gets hotter
If the engine genuinely is "cooking" after the hill climb, the fans should still run with the ignition on
(stupid ECU logic can defeat this but it does work on many cars)

When you turn the engine off, if it's very hot and the thermostat is open
The cooling system becomes a primitive thermo-syphon with convection system,
until the thermostat closes, at which point you don't have anything to worry about

In my Nissan Pulsar (SR20) I have removed the air con but retained the air con (radiator) fan which I operate via a manual switch
I also have an after market water temp gauge
After a race it's common for the water temp to be 95 degrees
When I turn the engine off the water temperature does not increase, there is no problem with heat soak
After a 45 minute enduro race on a hot day the car came in at 100 degrees - I turned the engine off and the fan on, no problem at all

I'll often turn the heater to hot coming off track but that's a shocker through summer.

Oath - need to get out of the car ASAP

[h100vw]

It's not that the water gets hotter

If the water isn't getting hotter, what is causing the switch in the radiator to trip?

There's nothing in this Polo to turn on the fans except the switch. It's a dumb system. No external influence.

Gavin

[sambb]

Martin where in the cooling system do you take your coolant temperature measurements? Wondering if VCDS looks at the engine coolant temp sensor, some feedback from the radiator fan switch or a calc of both?

[Martin]

If the water isn't getting hotter, what is causing the switch in the radiator to trip?

It's not that the water is getting hotter "when the engine is turned off"
The water temperature from his hill climb run is what would trip the fan switch

[Martin]

Martin where in the cooling system do you take your coolant temperature measurements?

The top radiator hose is a good location - that's the hot water inlet into the radiator

I used an inline hose adapter like this:
(So much easier and safer than drilling & tapping into engine parts which are mostly alloy)

Wondering if VCDS looks at the engine coolant temp sensor, some feedback from the radiator fan switch or a calc of both?

Depends what type of water sensor your car has
If it's an actual temp sensor connected to the ECU then VCDS can display the temp reading
If it's a sensor that switches at a set temperature then it's just an on/off switch which will be driving a relay to turn the fan on

Switches and relays just turn electricity on/off - they don't give feedback

[sambb]

Just thinking out loud here but if I run the slightly cooler thermostat (so that I know its open a tad longer when the car is parked up), finding a way to force the electric water pump manually might have merits. Surely I could log that output against water temp to get an idea of when its switching and then stick in a manual override or double its on time with a timing cct or something. argh I'm running out of places to hide switches!

[sambb]

That looks like a good little setup you have there. Yeah totally agree with you regarding the idea of fan switch feedback. That's why I was a bit confused by some of the things that I was told by the shop where I was going to get some bits. They seemed to be saying that the 'fan control system' was looking at engine coolant temp (an actual sensor) and also the fan switch temperature - suggesting that there was feedback from it. I wanted to change to a lower temp fan switch in the belief that this would by way of a dumb switch just turn the fans on earlier, but they said this would confuse the ECU and that the engine coolant temp sensor would just override the switch anyway as though it were some kind of master signal. I then did a bit of reading and found that there seemed to be multi pin plugs for these fan switches so I started to think that maybe they were right and just parked the idea.
I'm just going to instal an 82 degree (cracking) thermostat if I can find one locally, put in a switched bridge on the A/C pressure switch to use that fan for auxillary cooling and leave the rest alone I think.

[Martin]

Just thinking out loud here but if I run the slightly cooler thermostat (so that I know its open a tad longer when the car is parked up), finding a way to force the electric water pump manually might have merits. Surely I could log that output against water temp to get an idea of when its switching and then stick in a manual override or double its on time with a timing cct or something. argh I'm running out of places to hide switches!

Hmmm

Personally I would not change the thermostat
Millions of cars world wide are turned off every day with the water temperature at 90 degrees - it's not a problem
If your engine water temperature really is over 90 degrees then the thermostat will remain open and you may well be able assist the cooling process

Logging the current operation of the electric water pump and water temperature may not give you a correlation
This is because modern cars often have interesting control logic using multiple inputs

Will the electric water pump actually help?
Depends if it's part of the main cooling system or just used to cool the turbo down
(I don't know which model Polo you have, if it's turbo or not, and my Polo knowledge is very limited)

It should be easy to wire a switch into a relay that turns both the fan and the electric water pump on - no problem there
If there is no turbo then I would certainly proceed with this approach - easy job (once you find a place for the switch - LOL)
(I guess even if it is a turbo this would be kind to the turbo temperature)

[h100vw]

It's not that the water is getting hotter "when the engine is turned off"
The water temperature from his hill climb run is what would trip the fan switch.

I accept that the fans may run due to the heat from the run up the hill. While the engine is on. High load not a massive throughput of air potentially, if the speed isn't really high.

However, the point I wanted to get across is, that heat soak from the engine can elevate the water temp enough to trip in the fans. After the ignition is switched off. They don't run by magic.



The temp sensor is in the outlet on the side of the head. It feeds both the gauge and the ECU. Should be the hottest part of the system.

The fan switch is in the radiator, the battery side. It's just a bi-metallic switch. The electric pump circulates water through the turbo, whether that causes flow through the radiator, I couldn't be sure without looking under the bonnet. I would expect it does, a larger volume going through the turbo would move more heat faster.

The fan switch goes into the fan controller which is under the battery. This is the bit that switches the high current of the fans.

Volkswagen - PO - 2007 - Electrical Teile Katalog (Pats Catalog)

https://www.google.com.au/search?q=1...O4OwjwPciqDQDQ The fan controller. item 13.