Cooling system puzzlement

[fendervg 29]

Hi all - after about 6 weeks finally got the front end back on my car. The initial problem was a bad coolant leak, which turned out to be a cracked thermostat housing where it joins the block. It took me three tries to get it all back together and water tight with no leaks. I replaced all of the following with new VAG parts:

 

- all of the 3 part housing

- crack pipe

- thermostat

- the 3 sensors

- new seals all round

- oil cooler hoses

- bottom radiator hose

 

Car drives well, but the coolant temp gauge shows 70-80 C, when cruising. Oil temp sits between 90 and 104. I thought it might be a bad stat, but had tested it before fitting, and the top hose warms up normally, and then the bottom as it warms up. I checked the blue temp sender temperature reading with VAG-Com, and this showed 84 C after a good run with the fan kicking in. I would have thought the gauge would sit at about 90 C most of the time, and no higher than 80 C seems a bit low. Is is possible I have a bad sender, or is the temperature too low anyway? If it is the stat, I'm not looking forward to diving back in there again - has anyone ever managed to just undo the bottom thermostat housing for replacement without the whole front end off?

 

Oh, and as an aside, make sure you test your bonnet release thoroughly before you close it all up - it may slacken a bit after time, and it actually takes quite a lot of force with a pair of pliers on the cable end to pull it taut enough. Leave the grille off until you are sure it is right.

 

 

Cheers in advance for any help or advice.

[daves16v 1]

Those temps look normal to me, I get the same on the motorway and I've replaced all sensors, radiator and rad switch. Infact I've replaced all parts of the cooling system recently including both water pumps.

[Jim Bowen 1]

I got the whole housing off to do my stat. Needed to remove coil pack and the engine cover above it. Not too bad really.

[Supercharged 2]

It's too low according to VAGCOM then - maybe worth trying another stat and checking the mix is correct.

[vw rule 19]

Hello Fendervg,

most of the German cars have a thermostat that should open at 87c

 

I think the K series Rover engines thermostat opens at 92c, that's why their head gaskets are always prone to going.

 

There are some thermostats that open at a lower temp, around 80c

but these are normally fitted to engines that produce a lot of heat, like a turbo / supercharger engine.

 

When you're driving your Corrado the temp gauge should read when hot around 80c to 85c max

and when you're parked up still with the engine running the temp gauge should rise up to 90c or 95c max

 

Your radiator cooling fan senser switch should operate at 87c to 88c and in turn switch the radiator cooling fan / fans on.

 

You say you bought your thermostat new from VW (VAG) so it should open at 87c

I doubt you've been given one that opens at 80c

 

It could well be your temp sender is giving your gauge a false reading.

 

Also you have said that you tested your new thermostat before fitting it, so it should really be working ok i.e opening at 87c

Do you have slight pressure with in the coolant hoses, as you should have some at that temperature of 80c to 85c

as the thermostat also acts as a sight restrictor of the water flow.

Because when you have no stat fitted there is then no restriction of flow.

 

Your thermostat should like I say open at 87c and then should close once the temp has dropped down in the engine block below 87c

so your stat should open and close to keep the engine at a constant temperature.

 

The other thing you can do is to obtain a laser thermometer so you can test the engines temp from the engine block and cylinder head,

just to check that the engine is running at the correct temperature.

 

Or you can test the temp sender it's self by testing the resistance with in it,

all you do is use a multi meter set it to ohms and test the resistance,

the resistance should be around 200 ohms or above when the sender is cold,

and then should drop down low as the sender heats up (resistance should drop down way below 85 ohms when hot)

if not then it's a duff temp sender.

 

Hope this helps.

 

Si :thumbleft:

 

---------- Post added at 12:08 AM ---------- Previous post was at 12:00 AM ----------

 

Also what mix of anti freeze have you put in the cooling system ?

 

Si

[fendervg 29]

Cheers for that. Not really in the mood to take the thermostat out! I'll check the sender first this evening - I still have the old one so can swap it out.

 

The anti-freeze mix is 60/40.

[g0ldf1ng3r 13]

Those temps look normal to me, I get the same on the motorway and I've replaced all sensors, radiator and rad switch. Infact I've replaced all parts of the cooling system recently including both water pumps.

 

Hi daves16v

im in process of organising a top end rebuild & some other bits with stealth & have been pondering whether or not to ask vince to replace my water pumps & temp sensors whilst the engine is apart & as i am replacing all coolant hoses.

Presently i dont have any cooling issues but im thinking it might be a wise move to replace them when the work happens rather than have to fork out for more labour should they fail after the work

can you recall the costs of the sensors & water pumps? & did you use VW or OEM parts?

thanks :)

[dr_mat 0]

My VR sits at a reported 80-85 degrees when moving in cool air. Thermostat opens at 82, I thought.

If it's below 80, really if it's ever below 80, my guess would be your thermostat is a bit leaky and not closing properly.

[fendervg 29]

All the parts I bought were new from VAG - the housings and seals can be had from VW for about €60, crack pipe was €27, and the sensors another €60 for the three. Thermostat is about €20. All still available from the dealers, although I usually buy direct from Germany as they tend to get the parts quicker. Don't go for generic parts for this lot, it's not worth it because of the labour required to get at the cooling system - any non OEM thermostat housings I've seen did not fit together perfectly and a couple were not even flat on the part that fits to the block. Also get new bolts for the housing, as the old ones will be well rusty and make sure not to overtighten them as they shear real easily.

 

I can check all the part numbers and prices for you if you want.

[daves16v 1]

Hi daves16v

im in process of organising a top end rebuild & some other bits with stealth & have been pondering whether or not to ask vince to replace my water pumps & temp sensors whilst the engine is apart & as i am replacing all coolant hoses.

Presently i dont have any cooling issues but im thinking it might be a wise move to replace them when the work happens rather than have to fork out for more labour should they fail after the work

can you recall the costs of the sensors & water pumps? & did you use VW or OEM parts?

thanks :)

 

Will have to have a look thru my receipts later.

[g0ldf1ng3r 13]

thanks fender & dave!!

 

i already have a thermostat, housing & seals etc from VW in a box ready & waiting

 

I will get onto the stealer about sensors & housing bolts

 

thanks too for offering to check your receipts later dave - with the quote im already looking at im hoping the pumps are not too expensive but even if they are i think it might be wise to change them anyway

[fendervg 29]

I think it's worth doing the lot in one go if you can afford it - the problem with the cooling system is that once you replace one piece with new, that tends to highlight a weakness somewhere else, for example a new water pump will raise the pressure in the system a bit, and you may find that some of the hoses or flanges give way. I had this with a MkII GTI and it was an absolute nightmare to fix it all, as soon as one leak was gone, it would spring another one somewhere else! In the end I replaced the whole lot, and in the end the whole car with a Corrado ;)

[g0ldf1ng3r 13]

I think it's worth doing the lot in one go if you can afford it - the problem with the cooling system is that once you replace one piece with new, that tends to highlight a weakness somewhere else, for example a new water pump will raise the pressure in the system a bit, and you may find that some of the hoses or flanges give way. I had this with a MkII GTI and it was an absolute nightmare to fix it all, as soon as one leak was gone, it would spring another one somewhere else! In the end I replaced the whole lot, and in the end the whole car with a Corrado ;)

 

thanks fender - you have pretty much confirmed what i was thinking :)

 

i had better mail vince & ask him to adjust the quote

[tony_ack 0]

I replaced the thermostat (VW), crack pipe, housing, water pump and radiator (VW) and got almost exactly the same temps on the gauge - about 75-80 deg on the motorway and then up to about 95 in traffic. To be honest most old VWs I've had have run a little cold, I really can't explain it, especially after I replace the thermostats with VAG ones! Oil temp remains normalish - about 95 under normal driving, up to about 110 on the motorway, and 120 if I'm feeling spirited.

 

The only other things I can think of are that the dash gauge might be reading wrong, or it *could* be the grille. Some grilles have the top two slats blanked off, whereas others have all the slats open. Not sure how much of an impact this will have on the dash gauge. In theory the air flow to the rad should increase by a fair whack with the slats open, but then surely the overall system temp should still be regulated by the thermostat?

[Kevin Bacon 5]

The dash gauge is a LOT slower to react than the coolant temp sensors are. My VR used to get up to running temperature (yep, mid 80s is normal) within a few miles, but the dash gauge would still be just about crawling past 70 by the time I got to work.

 

I never investigated it dash gauges are only a rough guide anyway. This is why for the MK4 platform onwards, VAG engineered the gauge behaviour to always be in the middle (90 deg) no matter what, even when the actual temp is about 110, to stop paranoid customers constantly ringing the dealers! People are comfortable with the 'middle'. Either side of that and they start to worry (needlessly).

[g0ldf1ng3r 13]

This is why for the MK4 platform onwards, VAG engineered the gauge behaviour to always be in the middle (90 deg) no matter what, even when the actual temp is about 110, to stop paranoid customers constantly ringing the dealers! People are comfortable with the 'middle'. Either side of that and they start to worry (needlessly).

 

Thanks kev!!! i have always wondered why nearly all other VW's ive been in had a dash reading around 90 but my VR sits around 70!! lol

[fendervg 29]

Yeah, it keeps plenty of people worried - just have a look at the sticky "definitive VR6 cooling thread" in the Engine section here!

[daves16v 1]

thanks fender & dave!!

 

i already have a thermostat, housing & seals etc from VW in a box ready & waiting

 

I will get onto the stealer about sensors & housing bolts

 

thanks too for offering to check your receipts later dave - with the quote im already looking at im hoping the pumps are not too expensive but even if they are i think it might be wise to change them anyway

 

Aux water pump £106.33 VAG

Main water pump (metal impeller) £38.28 VW Spares

701919369D Sender £35.12 VAG

025906041A Sensor £19.09 VAG

1H0959481B Thermo Switch £27.61 VAG

 

I didn't buy the Black (high speed fan) sensor, I figured the engine would never get that hot with my miles and driving style.

[fendervg 29]

I remember the aux pump isn't cheap - some people just get rid of it and haven't had any issues.

 

I put my old (yellow) sensor back in this evening (those little clips are definitely not field serviceable units! Once gain the Corrado calls for a mechanic with incredibly long and anatomy defying flexible thin arms with little hands) . Went for a good spin, mixed motorway and back roads, and the gauge sat at a steady 80-85 with the oil temp at around 95-105. Came to a stop, let it idle and it went to 90 and fans did their business.

 

So there's a definite 20- 25 degrees difference between the two sensors - maybe I have a bad one. I'm not the best with a multimeter - obviously I set it to ohms to measure resistance, but I have a choice of 200, 20K, 200K etc. Which one do I pick?

 

Next problem is the fan bearing is making a horrible sound - better prepare the wallet for some GBH.

[daves16v 1]

The oil temps will always be higher than the water temps (gauge) on a run with no or little stopping. The water temp will rise when stationary for long periods.

 

Those temps are normal, my cooling system is 99% new and I get the same temps with similar driving conditions.

 

If you have a noisy fan then yes get ya wallet out!

[vw rule 19]

I believe you set the multimeter to 200 ohms or for a higher reading above that set it I think to 200K

 

The resistance on the sender when it's cold should be 200 ohms or slightly above,

and once the sender heats up the resistance level should keep dropping to a low reading say around 85 - 75 ohms.

 

So if you don't get any similar readings like above then yes I'd say it's a weak / duff sendor.

 

 

Hope this helps.

 

Si :thumbleft: