Where does your needle sit (seen this question lots of times

[CJH]

Yes I see your point. There will be times on a hot day, and if insufficient air is cooling the radiator, that the temp will rise and the rad fan then kicks in to help with cooling.

Yes, that's what I'm thinking. But specifically, since my fan hardly ever cuts in (unless it's a hot day and I'm idling in traffic), then I think my needle can happily sit in that gap between the thermostat and fan temperatures on a hot day. I definitely noticed this type of behaviour during this summer, but without a means to check water temperatures I'm only guessing what's going on.

[AdrianC]

The other factor is, of course, that coolant temperatures will differ relatively wildly around the system. You've got two bloody great big badly-insulated drainpipes dangling under the van. You wouldn't expect the water coming out to be the same temperature as the water going in - especially when the outside air is colder. The standard cooling system is capable (in good order) of coping with 50degC ambients. It doesn't need upgrading in the UK, just maintaining.

[ghost123uk]

The other factor is, of course, that coolant temperatures will differ relatively wildly around the system. You've got two bloody great big badly-insulated drainpipes dangling under the van.

On that subject, I often wonder how much (cab) heat is lost via the long uninsulated heater feed hose when batting down a motorway etc in minus temperatures ?

[danmetallic]

Will definitely be running this resistor test on my gauge circuit
http://www.thesamba.com/vw/forum/viewtopic.php?t=464113" onclick="window.open(this.href);return false;

I seem to be continuously running high.

[ghost123uk]

Follow up from my case =

I bought one of these to test this subject

I have had great fun randomly pointing it at things

My temp gauge sits at only about 1/3rd the way up. It gets there pretty quickly and once there, stays there, unless I am in traffic jams, in which case it climbs to just above the led and the rad fan comes on. I have swapped the sender and checked the 10 volt feed to the gauge(s)= all good, so I assumed it was just the actual gauge reading a bit low and lived with it. However when I bought the above pictured infra red thermometer (at only £8 - Amazon link) on pointing it at the black plastic stat housing, engine fully warmed up, it measures only 72 degrees. I checked against a mates new(ish) car and his top hose measured 86 degrees. I am now assuming that my thermostat, whilst not stuck open, is opening at too low a temperature (faulty), so I guess I will have to buy a new stat and try it. My (later style) stat housing and bolts are in good clean nick, so I am hoping I have no issues there!

It was my stat. The funny thing is was that it was not "stuck open" or owt. I tested it in a pan of water on the stove, it was just way out of calibration, reaching fully open at 72 degrees instead of 87. I replaced it = took about 20 mins from start to putting the engine lid back on. All good now, needle bang on the middle and heater noticeably hotter. £10 on Ebay and a "proper make" too

Engines run more efficiently at their designed temperature and the heater will work better = if in doubt change it !

[Smcknighty]

Mine once I'd sorted all niggles sat straight in the middle. It takes longer to reach temperature than my car due to having more coolant I guess (and a weedy 1.6 engine) but it reaches it fairly quickly and stays there. If it's moving a lot id say there are more things to sort.

It's been stuck far left since I took the engine out for my restore work 9 months ago mind..

[MidLifeCrisis]

The other factor is, of course, that coolant temperatures will differ relatively wildly around the system. You've got two bloody great big badly-insulated drainpipes dangling under the van.

Which makes me wonder - if the thermostat is fully open when the temp at the thermostat is 87 and the fan kicks in when the temp at the radiator is at 91 - then what is the temp at the thermostat when the fan kicks in?? Obviously it's more than 91 ........ but by how much (guess that would depend on ambient temps/air flow over the dangling drainpipes etc) ..... But would be interesting to know ???
(Also I assume that the radiator temp is measured on the output not the input? So it could be even scarier!!)

[ghost123uk]

The other factor is, of course, that coolant temperatures will differ relatively wildly around the system. You've got two bloody great big badly-insulated drainpipes dangling under the van.

Which makes me wonder - if the thermostat is fully open when the temp at the thermostat is 87 and the fan kicks in when the temp at the radiator is at 91 - then what is the temp at the thermostat when the fan kicks in?? Obviously it's more than 91 ........ but by how much (guess that would depend on ambient temps/air flow over the dangling drainpipes etc) ..... But would be interesting to know ???

I keep my I.R. temp gauge in my van, so next time I anticipate the fan coming on (mine comes on after about 15 minutes of ticking over, once already hot), I will point it up from underneath at the stat housing and report back.

[kevtherev]

The other factor is, of course, that coolant temperatures will differ relatively wildly around the system. You've got two bloody great big badly-insulated drainpipes dangling under the van.

Which makes me wonder - if the thermostat is fully open when the temp at the thermostat is 87 and the fan kicks in when the temp at the radiator is at 91 - then what is the temp at the thermostat when the fan kicks in?? Obviously it's more than 91 ........ but by how much (guess that would depend on ambient temps/air flow over the dangling drainpipes etc) ..... But would be interesting to know ???
(Also I assume that the radiator temp is measured on the output not the input? So it could be even scarier!!)

The radiator receives hot coolant direct from the engine and is cooled from the bottom up, if you look at the cut away it shows the position of the fan switch.



Clearly this is placed to read after the first pass through the radiator, so well before the fan comes on there is another row of cooling vanes to go.
Taking the temp of the returning coolant is the one to take, if your radiator is clogged then this reading will be higher than an average van, and the death spiral of over heating will ensue, fan or not your engine will overheat.

[lloydy]

The stat isn't fully open at 87deg though is it? Only starts to open at the temp, thought fully open was like 102 deg?

[California Dreamin]

The stat isn't fully open at 87deg though is it? Only starts to open at the temp, thought fully open was like 102 deg?

The 'opening' of the valve in a thermostat occurs at the precise point that the solid pellet of wax melts/expands pushing the pin outwards opening the valve.
However, the introduction of the cold coolant can and does result in the 'resetting' of the wax and closure of the valve. The opening/closing action continues until the thermostat sits in a constant 87 degree or above stream of coolant...it remains fully open from this point on as long as there is enough heat in the engine to keep all the coolant in the system above this threshold.
The thermo switch just controls the opposite end of the heat range (the acceptable running temperature range) from thermostat opening at 87C to second speed fan trigger of 93C, which I suggest is the max VW wanted this engine to run at.
However...and this has been pointed out, this switch is miles away from the engine and coolant has already gone through one vein of the radiator. Therefore, Its not hard to work out that 'Actual temps' in the cylinder heads must be quite a few degrees higher than this.

Q: So...what constitutes critical temperate and why?
A: When the coolant starts to boil.
?: Because the gaseous bubbles in the boiling coolant do not conduct heat away from the important 'Hot Spot' areas of the engine and cylinder head, causing massive localised Hot Spots, resulting in melting/warping/seizing of components .
FYI: The engines cooling system is kept under pressure of around 1 bar which results in the coolant having a resistance to boil up to around 114C depending on various factors. In a nutshell, Coolant under pressure has the ability to absorb more heat.
You now start to realise just how important it is to ensure that there are no leaks and components such as the pressure cap are functioning correctly.

One last point is with the 'very nice' radiator cutaway above ^^^^^^^^ Hot/Cold....lol....should be Hot and NOT so hot....the radiator just cools the coolant down by a handful degrees.

[lloydy]

The stats i have (diesel), have 87-102c written on them. Not trying to say I'm right, just a query really. wax stats that i come across at work expand linear with temp, hotter the temp, the more it expands and pushes against the spring and more cooler water is allowed to mix

[California Dreamin]

Have you ever heated a thermostat up in a proper thermostat testing kettle?

I have....with my students maybe 40 times in the 7 years I've been teaching motor vehicle technology.

Every single thermostat I've ever tested this way (lots of different makes from lots of engines) opening FULLY and almost instantly (2 - 4 seconds) as soon as its 'stamped temp is reached (unless it's faulty of course).
No part opening or gradual opening as temp rises...sorry mate.

Martin

[lloydy]

thats fine, again not saying i was right. Just interested now why the stat has 87-102c stamped on it

[California Dreamin]

I'm confused with yours TBH .... you are saying that it has the two temps stamped on it but I ca'tn honestly remember seeing such a wide range on a stat like that.
When they have two numbers they are normally pretty close for example: 82-84C .
Is this a standard unit? yours is a 1.9TDI?


Martin