8v water / oil temp problems...

Discussion in 'Mk2' started by sam jelfs, Mar 15, 2018.

  1. sam jelfs New Member

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    Hi all, been doing some searching and not been able to find any answers, so here goes...

    I have a '91 8v gti, which for as long as I have had it never got hot. Recently the water pump started to leak, so I swapped it out, and at the same time changed the thermostat for one that wasn't stuck open... Ever since then it's has been getting too hot for my liking. On the drive to work (mostly 50mph roads, a bit in town, around 10 miles) the oil temperature will hit around 104-106 on the MFA, but the water temp won't reach the 1/4 line on the gauge. On the highway I can see oil temps hitting around the 114c mark on the MFA. Even showing oil temps of 106c the fan doesn't kick in until I have been stationary for a minute or two.

    Around a year ago I changed the fan switch, and both of the water temp sensors, but I wonder if I have the right one for the gauge. The supplier I use seem to list three or four sensors, I have no idea which is the right one, does anyone have the correct part number? It's listed as a PF motor, but I am not in front of the car to check.

    Other than a dodgy oil / water temp sender (I intend to change both to be sure) any other ideas? I have had the car a few years, and because the thermostat has been stuck open all that time I have no idea what things should actually be reading. It is also using around 1L of water every 300 miles or so, I have done a compression test and all seems good (155-175 psi on a hot engine), so don't suspect a head gasket, yet don't see much in the way of dropped fluid either.

    Any comments or suggestions are welcome :)
     
  2. Tristan

    Tristan Paid Member Paid Member

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    A typical 1.8 8v gti Digifant is a P B code. Mine runs around 90-95 on the dual carriageway on the oil temp, cruising 60-70 mph.
    Coolant gauge runs between straight up and the next white line to the left. Straight up when idling.

    Uses no coolant, at all, as it shouldn't.
    Fairly new aftermarket rad, new oem Stat, and a new Hella Behr oil cooler.
     
  3. sam jelfs New Member

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    PF is the engine with cat, and slightly lower power, rated at 79 kW instead of the 82 kW of the PB engine that was used in the UK.
     
  4. jamesa Forum Junkie

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  5. sam jelfs New Member

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    so I grabbed a quick picture, excuse the filthy engine...

    As I understand it :
    blue circle - Water temp sensor for ECU
    white circle - Water temp sensor for gauge
    Red circle - is that oil or water?

    [​IMG]
     
  6. EZ_Pete

    EZ_Pete Forum Junkie

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    Oil pressure, lower rated of the two sensors. Other one is on top of filter housing along with oil temp (closest to block).
     
  7. EZ_Pete

    EZ_Pete Forum Junkie

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    Coolant gauge sender should be part number 251 919 501 D, I believe.
     
  8. EZ_Pete

    EZ_Pete Forum Junkie

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    Check to see if there's residual pressure in the expansion tank if you open it when the engine is stone cold.
     
  9. sam jelfs New Member

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    The one with the yellow wire? (just making sure ;) )
    [​IMG]

    Thanks, part number is useful.

    No residual pressure when the car is stone cold. I know I have a leak somewhere as it does drip a bit of water when it's parked up. Think its from the flange on the end of the head, where it goes out to the heater core. Going to change the tank as well, just to be sure, want to get as many parts together before I drain the coolant yet again.
     
  10. EZ_Pete

    EZ_Pete Forum Junkie

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    Yellow wire/white body is the 1.8 bar oil pressure switch.
    Oil temp might be that one with heavy green corrosion. Can't recall the wire colour just now.

    I might just have a spare new coolant flange, albeit one with a sensor fitting in it.
     
  11. sam jelfs New Member

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    nice one, thanks for the help. I'll get a few bits ordered up and have a play this weekend.
     
  12. Tristan

    Tristan Paid Member Paid Member

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    Typically the Alu of the head has some corrosion under the flange, so have s sanding block, a new o ring and some Dirko or similar.
    I wonder is your new water pump cavitating? Pressed tin or cast / plastic formed impeller?
     
  13. rubjonny

    rubjonny Administrator Staff Member Admin

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    yep the heavily corroded one is for the MFA oil temp display, its actually the wrong one if its a genuine VW sensor as the oil sensor should have a white collar. black collar ones are for coolant temp and a different rating so could explain why oil temp displays so much higher than the coolant temp (1/2 on the gauge is roughly 90 degrees) if its a pattern sensor then it may be correct, they dont always follow the VW colour coding system.

    have a look here to make sure all is well coolant side:
    http://clubgti.com/showthread.php?145091

    it is correct the fan shouldn't run until you've been sat for a while, what temp did the gauge show when it finally cut in?
     
  14. sam jelfs New Member

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    So over the weekend I drained the system down and replaced the expansion tank (with new blue cap), the flange on the end of the head, the water temp gauge sender (again!), the thermostat (again!) and the oil temp sender.

    Now when I use the car the oil temp gets up to about 112-114c on the MFA, but I think I know what is going on... Water temp gauge gets to halfway and stays there. If I come to a stop after a minute or so the fan kicks in, runs for a lil while then kicks back out again. I actually think the cooling system is all working correctly.

    Cleaned the head off with a scraper, and fitted up with a bit of Curil T, all seems good.
    New pump is a metal impeller, but I don't know if it was stamped or cast (I didn't pay that much attention when fitting, and it was a complete unit including housing)

    I'm fairly sure its the wrong oil temp sender now. One supplier listed it as the oil temp sender, the local parts place only had it listed as a coolant temp sender, but the same manufacturers part number (JP Group). Guess I need to hunt down a correct white collar sensor.

    This morning when I arrived at work I stick a thermocouple on the side of the oil temp sensor, and it read 82c, shoved it down the dipstick tube into the oil in the sump and it read about 86c, all while the MFA was reading somewhere north of 106c... Looks like all I need now is to find the correct oil temp sensor and stop worrying...
     
  15. rubjonny

    rubjonny Administrator Staff Member Admin

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    yep recon you're pretty much done :thumbup: oil sender is 049919563A Vw still have them at 19.31+VAT. local TPS branch usually gives you a little discount on that
     
  16. sam jelfs New Member

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    Nearest TPS is something like a 450 mile round trip from me, think I'll try the nearest VW main dealer first ;)

    Annoyingly when I search the parts place I normally use with that part number it returns the water temp sensor that I bought the other day and is wrong, useful!

    Thanks for the help everyone [:D]
     
    EZ_Pete likes this.

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