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Thread: 1.8T seems to be overheating for no real reason...

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    Default 1.8T seems to be overheating for no real reason...

    So, we identified this when on the last trackday, it went up to 120C of water and light started blinking.
    I was hammering it of course, and we thought it could be the radiator was too small (smallest for the mk2 Golf). Changed it to the biggest for mk2's.
    Changed radiator, and cut the thermostat so it was flow through.
    Flushed the system, changed waterpump and belt (it was due) and tested it again.
    At idle, it will keep on raising temp, even with the fan working (Mishimoto slim).
    Fan kicks in at 87C, but temp will go high as 100+ at idle. Never goes down.

    Could the thermostat elimination made it climb like that? Or can there be any other issues?
    Also, we CO2 checked to see if the headgasket was bad, and it isn't...

    Any tips?


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    what did you do for the dash coolant sensor, as the mk4 one doesnt work correctly with the mk2 clocks. is the mfa oil temp working? another thing you can do is read the ecu measuring block for the coolant temp to make sure the dash is reading correct.

    how is the fan mounted as well, if its just strapped to the rad it wont work very efficiently as it can only cool a small section of the rad core. you could add another fan or build a shroud for it to force it to pull it thru the entire rad
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    The sensor is the one for the ABA, as it will provide good readings for the ECU (Megasquirt) and also, will be OK for the mk3 clocks.
    The MFA oil is reading as well.

    The fan is mounted on the radiator, just strapped there. No shroud. I'm thinking of putting another next to it, doubling the cooling (1 takes half of the radiator).
    Not sure why it started to raise the temps, but after reading on another forum about the possibility to have air locks, it makes some sense.
    The water reservoir is connected to the slim black pipe, underneath the coolant flange where the sensor goes, etc.
    I have no heater, so the air might be trapped on the top of the engine (let's put it this way). I will do something to try to take the air out from there (if there is any).


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    yeah the mk3 one should be fine, I think you're probably right by the sounds of it theres an air leak
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    So, we changed some of the pipes etc getting it the same way as the original diagram.
    Changed t-stat.

    Temp Sensor is good
    Fan switch is good.

    Car is still overheating. While driving, it's now running at around 80c(176f) (82C(180f) is the t-stat opening) and all good there.
    If I stop and let the car idle, the temp will go up to 105C+(220f).
    Fan will kick in when it's supposed to, but will never stop.
    Can't get why this is happening, and I'm running out of ideas...
    This didn't happen before. Trackday is at the end of the month, and this is not looking good


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    if the temps are fine while its driving around, then your radiator & stat are fine. it sounds to me like your fan isnt big enough and/or cannot work efficiently due to the lack of shrouding
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    I had another fan, without shroud and it never ever did this up until recently. Then changed fan, still without shroud, and it's the same. We will put both fans there to see if it works better. Can a relay output less amps and make the fan slower?

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    I suppose if the relay was starting to fail it could do that, I know when my fuel relay went bad it could only supply enough power to run the lift pump at times
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    What about oil temps? What are they showing?

    If your oil is getting hot, that will transfer to the water.

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    At the time I tested this last night, I was able to see the oil temp in MFA, and it was showing 72c. I assume that is not that bad.


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    Is there any possibility that the fan is running the wrong direction?
    PEACE THROUGH SUPERIOR HORSEPOWER
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    Quote Originally Posted by HidRo View Post

    Could the thermostat elimination made it climb like that? Or can there be any other issues?
    Cutting middle out of the thermostat will keep it cooler.

    Have you recently changed ANYTHING. eg, Oil type / viscosity? Spark plugs?

    Basically, look for anything at all that you've changed, however unlikely it seems.


    Check the timing belt hasn't slipped, that could possibly be a cause.

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    Shane, it is working in the correct way, sending air from the radiator to the engine.

    Nige, I changed to another type of oil, but recently. It overheated on the track before that, so oil is out of the equation.
    Sparks are the same. Maybe I'll change for new ones, but they are BKR7E's
    We changed the timing belt when we did the water pump, and it's spot on. Also, it overheated before changing belt.
    Would a slipped belt overheat on idle? It does run fine and cool when driving.
    Without the center piece of the t-stat it is too cold. It will go for ~60C. Well, maybe while driving on the track, it might get to a good temp.
    The only thing we changed that would be something to notice was the water reservoir location. It went from one side to the other (it's not at the stock MK2 location).
    We saw that the black thin pipe was changed in a way that could impact this (not allowing proper circulation) and we changed it back to making it circulate correctly.
    It's the same...

    The car pulls strong, even at 0.7/0.8bar so I THINK I might not have bent valves or something that could cause everything to run extra hot.
    I can't think of anything else to try
    Last edited by HidRo; 12th September 2017 at 22:36.


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    Ok, was worth asking.

    So, just to clarify. It is fine when on circuit and ONLY overheats when stationary and this started suddenly before you changed anything, apart from the location of the header tank?

    If the header tank is lower than before, that would make an airlock much more likely. Personally, I'd temporarily refit the header tank back where it was, just to discount that as the cause.

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    It overheated on track. That is what lead us to do all the work we are currently doing.
    Not, as I'm preparing to go on track again, I was not able to test pushing it hard enough to see if it overheats while driving as on track.
    At the moment, driving at cruising speed of 120km/h with the t-stat cut, it will drive at 60C+. With the 82C t-stat, it will drive at 80C+. If I stop and let it idle, it will start to climb all the way.

    Changing the header tank back to it's previous location is not feasible as we changed the IC piping and it's in the way of where the tank was.


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    right so you can put the thermostat back to original, its not causing the overheat and will give you more problems in the long run as the engine will be running too cold most of the time.

    for earlier cars without a header tank sometimes people have to take the top hose off and fill the rad direct as they are a little more tricky to bleed. For it to work effectively the tank has to be higher than the engien ideally, plus the thin hose to it wants to be as high on the system as you can get it, and in a pipe which is always seeing coolant circulation even with the stat closed. MK2/3 golf usually have them in the radiator or the top rad hose. If you can plumb your tank into the factory pipes used for the 20v that should be fine anyway.

    have you read this, the bleeding method in there has never failed me:
    http://www.clubgti.com/showthread.php?145091
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    Quote Originally Posted by HidRo View Post
    It overheated on track. That is what lead us to do all the work we are currently doing.
    Not, as I'm preparing to go on track again, I was not able to test pushing it hard enough to see if it overheats while driving as on track.
    At the moment, driving at cruising speed of 120km/h with the t-stat cut, it will drive at 60C+. With the 82C t-stat, it will drive at 80C+. If I stop and let it idle, it will start to climb all the way.

    Changing the header tank back to it's previous location is not feasible as we changed the IC piping and it's in the way of where the tank was.
    I have the same problem on track but with oil temps, which will eventually overwhelm the cooling system given enough time.
    This is an ABF NA engine with significantly more engine power than stock.
    I am currently attempting to shortlist what is the root cause and a permanent fix is based on the history I have on my own vehicle.
    I am not going to list what has been changed due to time but I am narrowing how this phenomenon occurs to two sources before shelling out.

    Possibly exhaust backpressure transferring high EGTs to the exhaust port cooling jackets
    Actual undersizing of the double core alloy 16v radiator.

    JENVEE also runs an external MOCAL oil cooler in addition to the OEM Water to oil design.

    On road the trend is there to heat up the oil and more noticeable when ambients are over 20 deg C, with high part loads. However as you cannot legally/practically be flat out on the road there is no real concern.
    No issue at say 10 deg C ambient on the road, at any condition with oil temps no more than MFA 98 deg C on an Autobahn 110-115 mph sustained for 15mins or so.
    On a track over an MFA 130 degs seen for just 15mins of track time!

    *MFA readings are from a VDO cluster with matched OE senders.

    Money has been spent on quality components and OE parts, including an engine bottom end change with no impact on the issue.

    So my point is you have done the right steps but the root cause is likely to be elsewhere. I suspect at full chat on a boosted engine as yours,
    Your cooling system is unable to reject the heat energy from the engine when it is at its max friction, back pressure, and combustion temps.
    Without my own conclusions on my own vehicle, my gut feeling is to be track suitable, you will need to look at the radiator sizing and maybe the oil cooler sizing, on the basis your engine is the usual VW EA113 1.8T design, water pump in is good nick and along with a known stat.

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    I will try to bleed the system once more, and try to pull the header tank higher (holding it with my hands.) to see if it burps.
    This is how it's at the moment.
    The header tank is above everything I believe.
    Click image for larger version. 

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    As for the exhaust gases. Would this be something to consider, if we are talking about overheating at idle as well (not only on track, pushing hard)?
    I have no oil cooler other than the stock water/oil cooler. But Oil temps were up to 72C the last time I tested the overheating at idle.


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    If it's overheating and the oil is still only at 72C I would think it's not an issue of oil heating the coolant. Just my two pence.



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    Eddie, my understanding is nothing had changed hardware wise, the engine was fine and suddenly started overheating. Which would suggest that the cooling system was up to the job, then something happened.?

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    Nige, that is about right.

    So, today we did some more tests.

    We added the old fan (now making it 2 fans that take about the entire radiator. BTW, the old fan is a lot better than the new Mishimoto one :S) and went for a drive.

    Started driving, and it took the expected amount of time to reach the 80C. Then, slowly up to 89/90C.
    Let the car idle, and it went as high as 96, and back down to 91C.
    Took off again and if I kept my pedal to maintain the speed(120/140kmh), it will be around 90C. If I coast on a hill, it will come down to 86C.

    Some pulls, at 1.5bar will not raise the temp much (91C give or take).
    Park the car and let it idle, it will raise again up to 96C and back down to 93C.

    Oil was never over 80C (after the hard pulls) and 74C while driving normally.

    Night out is 20C.

    The thing is, not sure what happened to make it need the 2 fans instead of 1 to get the same results...

    On another note, I used to use BP Visco 7000 5-40 and changed to the LiquiMoli 10-60W "racing" oil.
    It seems the lifters are way louder... Some underlying issue or just the oil.

    Pffffff I'm feeling this is not going in the right direction.

    EDIT: forgot to mention. Both fans at full speed will never turn off at idle. I believe it's supposed to turn off right? And this is after driving normally and temps being at around 90C. Not pushing it hard.
    Last edited by HidRo; 14th September 2017 at 07:54.


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    they should eventually cut out yes, the OEM switch is set to cut in at 95 degrees radiator temp then switch off again at 84 degrees.

    looking at your picture the header tank position looks ok. the thin hose should go to the small outlet on the top hose plastic fitting thing, bottom hose goes on the metal coolant pipe round the engine. as long as yours is plumbed like that you should be fine, the systems self-bleed pretty well VW dont even specify a bleed method just fill it up, put the cap on then once its got hot enough to open the stat shut it off then fill it up once required.
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    Yeah, it is connected that way.
    When the car is running, we can open the header tank cap, it will be OK, so no excessive pressure (head gasket leak) and we can see it's flowing from the small hose. All seems to be OK.
    The switch I have is a 87-82 IIRC, but the temp will never go below 91C. So I'm guessing the engine might be running a bit hotter than it should? What would cause that?


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    could just be your thermoswitch is too cold then? the dash reading will always be a bit higher than the temps in the radiator as its on the hot side of the engine on the top hose. the thermoswitch is all the way over on the cold outlet end of the radiator so any coolant that makes it there will already have been cooled by the rad/fan, if you get me.
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    But wouldn't that make it worse, as in the water always being a couple degrees higher, therefore not cooling enough?
    I have another termo switch which could be tested. I'll give that a go.
    I do understand the temp difference, but we measure it also with a digital pyrometer.


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