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Thread: Overheating - Temp Gauge Shows 'hot' randomly

  1. #1
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    Overheating - Temp Gauge Shows 'hot' randomly

    Hi There,

    Am new to forum. Introduced myself on main page and would enjoy any advice that may be on offer.

    I have just purchased a used 1997 Golf - CL, immaculate condition with 132,000kms on the clock. Very tidy.

    One thing i have noticed in the last 5 days of driving it not very much is that it has randomly jumped from 90deg up to peak temp on the gauge (130deg).
    Its happened 3 times i think. Once i had been travelling at 110km for approx 15mins after a further 10mins inner city driving. I stopped and turned car off, checked hoses and coolant in expansion tank. Hoses were hot (how hot to normal? i don't know as i don't know what normal is on a golf). Coolant was above Min. mark but not overly.

    Second time i think it kind of fluctuated a little from 130 down to 110deg and then crept up again.

    Third time..just then I just drove to the local shop and it was on the standard 90 deg. Hopped back in the car after shop, went around the corner and noticed it on 110 heading towards 130deg. Stopped the car, turned back on and it stayed on 90 most of the way home (short distance - less than 5mins) but had crept up by the time i was home.

    OK - so i have a gut feeling that it may be electrical, how do i test (with a multi-meter?) if the sensor or sender unit is functioning properly? Can someone tell me where it is (i know i will buy a manual shortly but don't have one now).

    I am supposing that it may be a thermostat issue or possibly water pump but the times it has happened do not necessarily show any consistency.

    Any help is GREATLY appreciated...in order for me to be at ease that i haven't bought a lemon

  2. #2
    Super Moderator Lucas_R's Avatar
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    Probably the thermostat is stuck closed.

    Next time it happens, turn the heater on and see if it reduces the temp (uses the coolant heat to warm the air).

  3. #3
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    Pumps not really famous for failing in the impeller department. The stat could be sticking closed? Be careful running it up to max temp that you don't boil it over and wreck the motor.

    Are the fans kicking in?

  4. #4
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    Thanks for the replies to both of you!

    1) Yes the fans are kicking in i believe, i put the aircon on when i had the bonnet up and they came on so i believe that they are likely to work in all instances.

    2) I will try the heater if this happens on my way to dropping child to school this morning

    As i have heard the same advice re stat from both of you i would presume this could well be the case. I would assume however that it is 'sticky' not totally 'stuck'. as there have been different drive times and speeds etc. associated with the offending behavior.

    My next question is...whats the cheapest way of replacing it..part wise and labor? I have completed small to medium mechanical tasks in the past on different cars. I don't have a manual yet though. i replaced a head and gasket etc. on my old 75 two door passat and water pumps etc. on other vehicles..any way you get the picture. I don't particularly want to pay the local volks dealer to sort it out unless i have to.

    Assuming there may be a thread in the forum that someone can point me towards.

    Thanks again guys!!!

  5. #5
    Super Moderator Lucas_R's Avatar
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    So your car is a Mk3 Golf CL or GL? So that should be a 1.8L single cam engine right?

    Basically a cars cooling system is quite simple, so if you are overheating it should be relatively easy to pinpoint – especially in an older car as they are much more simple than modern engines:

    - Thermostat stuck (can be stuck open/closed/or somewhere in between). If stuck closed the engine will overheat (worse on hot days), if stuck open the engine will never warm up properly (or take a long time) etc etc.
    - Water pump failed or in process of failing (eg impeller is broken and is not pumping enough water around.
    - Belt driving the water pump is either broken/missing or slipping. If this is the case, then the water pump will not be operating correctly. Check the belt is in good condition and nice and tight.
    - Radiator is not full of coolant (also check overflow bottle has coolant in it) or there is air in the system.
    - Blockage somewhere in the rubber radiator hoses etc not allowing water to circulate through the system.

    In modern engines, manufacturers have a habit of bundling the thermostat in with the water pump, meaning that a simple thermostat failure requires you to replace the entire water pump assembly – a costly exercise and something the average home mechanic cannot do. You might be in luck with the older Mk3 that you have a standard thermostat setup, where the thermostat and gasket cost around $30-40 and you can replace it at home with the most basic of tools. I replaced the thermostat on a mid-90’s Ford Laser recently for a friend and it only took around 20-30mins and cost less than $30 in parts. In that car, the thermostat had stuck open so the car never warmed up properly and the heater wasn’t blowing hot air to warm you up on these cold mornings. That Ford Laser was very easy to work on and the thermostat was very accessible, so the job was very easy to do. Once the thermostat was replaced, the engine warmed up correctly and there were no further issues.

    I have worked on a Mk3 Golf a few years ago (my wife’s little brothers car), and even though I did flush and replace the coolant amongst other things, I cannot remember the location of the thermostat nor it’s setup/design unfortunately.

    Best to Google the Mk3 thermostat info and then try to locate the thermostat on your engine and go from there: https://www.google.com.au/webhp?sour...+mk3+golf+1.8l

  6. #6
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    Thanks Lucas!

    So i have located it, on the base of the engine near the sump. A bit tight and tricky it would seem but saving grace is that it looks like it is a good old fashioned thermostat.
    The water pump has previously been replaced when the timing belt was done 24,000kms ago so i am hoping that rules this out. Also the random nature of the rise in temp would indicate inconsistency like a sticky stat.

    VW original parts supply wants $77 for a stat and O-ring. A guy in town who works on VW religiously has told me about $30 for the stat and $110 for an hour of labor should do it - i think i am going to save myself the hassle and go with that. At least i know he has done it before etc. I think i will get him to flush the system and replace with the recommended coolant (pink stuff) too.

    Thanks for the help again Lucas.

    Bendy

  7. #7
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    Hi Guys,

    It's been a little while, i had the thermostat replaced, flushed system and brand new G12++ coolant, they did a pressure test and that was all good too. 4 weeks later car started over heating once or twice but only up to 100-110 deg. Since then it's got increasingly worse and now overheating every time i go out...not over 110deg though - and yea i have driven it only little distances as a result when this has happened. If i pulled over and turned the car off, then on again, sometimes the temp gauge just goes back to 90 and stays there and off i go....although it is not doing this now.

    Fans do not seem to be coming on although i have tested them and they work when the switch is bypassed so obviously not fan motor etc.

    This morning after driving 3 mins to do school drop off it was at 105+ as i come to a give way t intersection, i do a right hander and the temp gauge drops 10 degrees going round the corner...

    I bought a new temp sensor for 12 bucks...cheap way of trying to isolate the problem.

    Basically i am thinking it is the switch or thermostat although the turning the corner thing says maybe an air bubble or sensor?

    Question is, is it not unusual for a thermostat to pack it in so quickly after being replaced?? And if so...is there anything that may have caused the thermostat to pack it in so quickly? It wasn't cheap to replace thermostat given its location and all the new coolant etc. Don't want to go doing this again and probably would have a crack myself if i did.

    frustrated

  8. #8
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    Progress..

    So i replaced the sensor today and sat it idling in the front driveway. it rose to about 97 and first fan went on then went to 105 and second fan came on.
    I drove it this arvo and it got to 105 going to school then on way from school to shops 90 deg...then home from shops 90 deg....will keep everyone posted

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