Overheating 16v - not head gasket (UPDATE: All fixed!)

[golddust 0]

Hi everyone,

 

I'm still after help. As I'm sure you will have seen I had grief recently when my engine overheated and I think blew the head gasket.

 

Anyway, I've just changed the head gasket, head bolts, oil, oil filter. Engine starts and runs. Sounds ok but...

 

... it's still overheating! I ran it on the drive for a few mins watching the water level. Once it was stable I did a careful once down the main road (about 1 - 2 miles). Never over 4k rpm or 70mph. Started getting steam from the expansion tank as I got home (no water).

 

SO, I topped it up and ran it on the driveway for about 5 mins. Gradually the temp went up.... and up.... and up. Water reached 110 and oil 122 before I turned it off. Immediately the expansion tank over flowed. Then runs out of water, then overflows etc etc.

 

The radiator is scalding hot so I presume water is flowing to it but the cooling fan never came on. Though it does when I wash the car...

 

There was oil in the expansion tank but I presume that came up when I did the head gasket so not too worried there. I just cant figure out why it's overheating!?!?

 

I'm on the virge of taking it to the VW dealership where I'll probably get a massively high bill so would be grateful of any advice on what I can check myself. Incidentally I'm not massively familiar with the VW 16v engine so if you say "check the thermostat" etc please tell me where to find it!

 

Thanks for any advice!

 

Incidentally also replaced over the last month:

Fuel filter, HT leads, spark plugs, rotor arm, dizzy cap, Warm up valve (blue plug on end of fuel rail).

[Supercharged 2]

I'd change the stat and the rad fan thermo-swich, changing the coolant again incase you have an airlock...

[golddust 0]

Would not having the rad fan coming on result in the water boiling like this? I know the rad fan is there for cooling the engine but I didnt think the engine literally boils after a few mins without it?

[Supercharged 2]

Hmmm - maybe at idle because of lack of airflow but not when driven - especiallty in this weather!

 

You could bridge the fan switch plug and run it continously (just to test)

 

Stat sounds ok as Rad is getting hot but it wouldn't be a bad thing to change it and the temp sensors also... may as well do the water pump as well!

[Skimask 0]

Valvers do airlock easily after you've drained the system. Usually, I use the garden hose to fill it up via one of the heater hoses. Do it gently though, don't turn the tap on full blast! I usually wait unitl the water comes out the other end of the pipe you've just removed. Reconnect the pipes and let it tickover - with the expansion tank off, and fill up as necessary. When you fell heat coming from the inside of the car, you're about there.

[chubbybrown 0]

Check radiator,check thermostat ( just remove it) and run on water and see what happens

 

try 12 volts straight to the fan and see if it goes

 

maybe a thermal switch ?

 

 

check thermostat by putting in boiling water and see if it moves,check the ° on it to make sure it will open below boiling of course !

 

usually a number on the head of them.

[thorpey 0]

check radiator isnt blocked i replaced mine which was easy to fit and only £42 at GSF also change thermostat as this ic only a few quid too,when refilling radiator do it slowly so no air locks

[golddust 0]

OK, so the general feedback seems to be:

Check the thermostat. - Can someone tell me where it is? (showing my lack of VW knowledge here!)

Full system flush to eliminate airlocks

Bridge the fan switch to see if having that on stops the overheating.

[aide 0]

thermostat is on bottom of water pump, you'll need to move the power steering pump which is a pain

 

bridge the thermoswitch with two spade connectors, there's three spade sockets - two speed supply and one earth.

[davidwort 0]

check radiator isnt blocked i replaced mine which was easy to fit and only £42 at GSF also change thermostat as this ic only a few quid too,when refilling radiator do it slowly so no air locks

 

Did you get an 8v carb rad from GSF?, that's what they sold me for my 16v, same dimensions but not the same number of cores in the rad, a real 16v one is more than twice that price.

How does your water and oil temp run with the GSF rad, mine seems a bit higher than I'd like, not too hot, but it doesn't seem to run spot on, about 106 degrees oil on steady crusing, water about right but tends to settle just above the mid-mark whereas it used to be bang on.

Doesn't help that I changed to a 2.0L Audi 6A block at the same time though, so I'm not sure of the effect that is having.

 

cheers,

David.

[G60JAY 0]

Could also be your water pump. Had a similar problem on a renault 5gt turbo(don't say anything). Rad was getting hot but the coolant was not flowing properly.

[golddust 0]

Hi everyone, I've done some more tests and am still unsure as to what to do next.

 

I flushed the water system and connected the rad fan so it was permanently on. Then ran it on the drive for 15 mins then a 5 min drive round the block. It didn't overheat at all :-) But did seem to use water still... There is white smoke from the exhaust but it's bloody cold so not sure if it's just weather related.

 

I checked the wiring on the loom to the rad fan which goes to a sensor on the bottom of the rad and a multi plug behind the passenger side headlight. I found the earth was fine at all point. There wires in the short rad loom all connected with a continuity test. On the plug behind the headlight the earth was good, the red wire had a 12v supply but the red/white one did nothing, though this was with the engine off.

 

My questions:

What controls whether the rad fan comes on or not and how do I test it?

Why might it be using water still?

[saysomestuff 0]

There is some info on this on "Almost an ex-Corrado owner" by me - my thermo has packed up, blew the seal on the expansion tank so it just pi$$es steam, but any breakthroughs you make - i would love to hear them, I hate not being able to drive it like its meant to be driven! :cry:

[golddust 0]

OK,

just made an important discovery... After several hours of reading posts about rad fans I've put 2 and 2 together....

 

SInce buying the car I've had a loose black wire with a spade connector next to the airbox but it couldn't reach any connector... When doing the head gasket I noted one rocker cover bolt had a sensor with a spade clip on it. This was right over by the distributer. I placed it back there but could find no wire to connect to it. I just tried earthing the mysterious black wire and hey presto the rad fan comes on! So now I figure that sensor on the bolt should be connected to this wire and must be in the wrong place, should be next to the timing belt?

 

Is the sensor on the bolt the ONLY sensor that controls the rad fan as my fan wasn't coming on at all before....? (Unless I made a direct connection to battery).

[chuck 0]

Sounds like your problem IS fan related.

 

I had all the same problems you describe last year, and all seems OK now.

 

If rad is hot ALL the way down, the thermostat is OK, and the likleyhood is the pump is fine too...

 

That sensor is an engine bay temp sensor - not directly linked to coolant temp. This is the sensor that will turn your fan on up to about 10 minutes after the car has been turned off (should have the temp stamped on it). It should be on the rocker cover bolt just by the timing belt at front.

 

THe thermoswitch at the bottom of the rad (where you would have disconnected the three wire pplug to bridge the fan, controlls the fan, directly on coolant temp. As i recall the standard thermoswitch operates the low speed fan at 95 degrees and the hight speed at 102. Not expensive from GSF.

 

Bridging this connector should produce 2 very different speeds on the fan - if not that loom is at fault. trace it back and check it is properly connected at the other end. If this bridging does work then the thermoswitch is knackered.

 

Also the time to heat up to running temp (90deg) is about 5 to 10 minutes at idle, though it might only take a couple of minutes after that to reach the first fan on temp, so unless air is rushing over the rad (from either moving or the fan)- it WILL overheat in about 15 minutes.

 

BTW, mine sometimes goes up to 110 before coming down again - tho the fan comes on well before this (and usually moreso in the summer - hasn't gone above 105 in a couple of months).

 

Oh, and the first few times you drive it after refilling the coolant, you will have to top up about half a litre or so as the airlocks gradually get forced around the system

[golddust 0]

Cheers for that Paul. To get the fan to go on I actually ran a spare piece of wire from the plug behind the headlight to the plug on the rad fan. I left the thermoswitch at the base of the rad alone. I'll try bridging that tomorrow, I presume just a bit of wire from the earth to each of the red wires in turn?

 

The car still seems to be very unstable with water. One minute the expansion tank will be overflowing, the next it's empty. Top it up and again it overflows! Then sits stable for 5 mins then overflows, etc etc. Over 20 mins on the driveway must have put in 20 litres, most of which overflowed onto the ground but still once the engine was off the expansion tank was empty...

[chuck 0]

20 litres with the cap on!!?? thats a lot :shock:

try replacing the expansion cap...

also try warming it up with the cap off - might help trapped air escape, but not so much that it gurgles over the side.

Be careful not to put cold water into a hot tank - you could end up with a cracked block.

 

to check that the pump is working, and that the water is not just simply boiling while static, check that there is a steady stream of water coming through the return pipe from the top of the rad to the expansion tank, should be a little jet of water noticeable with the cap off.

[aide 0]

I presume just a bit of wire from the earth to each of the red wires in turn?

 

There's 3 spade sockets on the connector, get a bit of thickish wire, put a spade on each end and plug and play :D should be two speeds, make sure your fingers are out the way....

[golddust 0]

Thought you guys might like an update...

 

The good news is that as of today I'm back on the road!

As you know the engine was still boiling water even with the fan bridged. I then gave it some thought and remembered that pressurised water has a higher boiling point.... Of course when things blew before the seal on the expansion cap and worse still the emergency overflow valve on the expansion bottle were both no longer airtight....

 

SO, I bought a new expansion tank (£14) and cap (£3.50) from German & Swedish. I also bought a new rad fan thermoswitch (£7.99).

I plumbed everything in (took about 30 mins) although this necessitated a trip to Halfords for a large 30mm socket for the fan switch which turned into a whole new socket set using Xmas gift vouvhers :D

 

Did a first run and was very pleased to find the fan cut in at 90 degrees but the important point is the water wasnt even bubbling! :)

 

Blatted it round the block again and no signs of distress so at present at least I'm happy to say it looks like it's all fixed!

 

For anyone else with water overheating problems I'd say don't overlook the expansion tank, I think it's been the saviour for my engine as I neared despair!

 

Anyway, thanks for the help/advice everyone! Hopefully this is now fixed for good, or until I can afford a 1.8T :lol: