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Thread: 300Tdi periodic overheating - no hot air & no idea

  1. #1
    Trainee cmsmwoo1's Avatar
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    Default 300Tdi periodic overheating - no hot air & no idea

    Hi All,

    I am now the prod owner of a 300Tdi 1994

    It's great to be able to see some of the work everyone is doing and my first job was to replace the bias plate.

    I have a question for some of the seasoned pro's out there...


    My discovery temperature gauge sits happily around half-way most of the time. If I drive it up hill (on the road even) it overheats in less than a minute. If I stop (and even at idle) the temperature starts moving back towards the middle again (slowly).

    I have only noticed once mildly warm hot air come into the cabin (been on full heat both dials in a variety of positions). The time it game on it made a funny gurgle type noise then went cold again sometime later.

    I check the pipes and particularly the top hose from the thermostat to the Rad and it almost suggests it has no water in it most of the time (and certainly when cold).

    How can i figure out which of the possible problems:
    Radiator blockage
    Dodgy Thermostat
    Dodgy Water pump
    Cylinder head
    Air locks

    I'm planning to flush the coolant tomorrow am and run a hose thru the head and rad. Some suggest rad core issues aren't obvious with a flush, and I have no idea how i can test if the water pump is working.

    Am hoping to do it all myself but am pretty useless - ruling out the water pump would be great! P.s. the poor thing was completetly bare of oil when i picked it up - drank 2.5L to get to the half way mark so am expecting this to be head trouble due to neglect - done 150k if that matters.

  2. #2

    Default Re: 300Tdi periodic overheating - no hot air & no idea

    I`d be looking more along the AIR LOCK lines if i was you
    Remove the rad air screw ( big plastic bolt head with slotted srew slot in it )
    on top of rad ,
    pour water into reservoir until it flows out of this opening,then close whilst waters still coming out,
    then open bleed valve on top of thermostat housing @again with full reservoir wait till water flows out before closeing. "if either of these dont happen" its got a blockage,
    if both do happen and you still overheat i would look towards pump,
    ive had a pump which the vanes (paddles) had worn down to nothing,
    chances are the rad wont be blocked if it bleed as in step 1.
    Its also unlikely a dodgy thermostat as it would boil over (if closed) and take forever to heat up if open.

  3. #3
    Engineer ComicalEngineer's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Start with the thermostat. 5 and 20 minutes to do.

    The stat is prone to sticking, and can do so in any position from wide open to full closed.

    The 300tdi is massively overcooled for UK conditions so I recommend starting with the obvious. When you re-fill it, fill to the top via the black plastic plug on top of the housing being careful not to shear the plug unless you have a spare or a brass radiator plug (better than OEM) to replace it.
    Disco TD5 auto (Nellie)
    Disco 300tdi (Rupert) gone but not forgotten

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    Apprentice symun's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Mine was/possibly still is doing the same, i changed the thermostat when it first happened which made the heaters work again for ashort while anyway. Every now and again the temp would rise(underload or on a hill) Have changed the thermostat again as they are so mass produced that the new one could have been effed, bled the system with the thermostat plug out until it boiled over, then the radiator one until that boiled over and fingers crossed the overheating has stopped.
    The heater on the other hand still doesnt work, but i am flushing the heater matrix as soon as i can to cure or eliminate that.

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    Trainee cmsmwoo1's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    thanks folks...

    today drained and flushed the rad. Also disconnected the two hoses going in to the bulk head (the in/out heading to the heater matrix - as well ran water thru the matrix to eliminate any issues but left it disconnected. Will post pickies when i can.

    Temp is ace during normal (flat road) running and idle. Obviously not worried about in the hot air in cabin now as bypassed it for now.

    Seems I also topped up at the thermo housing after a brief fire-up/pressurisation. The needle is rock steady for now but again I hit a hill between 2.5/3k rpm's and within a minute the needles almost touching red (pull over to allow cooling while idling).


    The water pump does sound a little suspect (metal on metal squeek/squeel almost like loose fanbelt but much quieter) but with all the air out of the system and a top up my expansion cap is showing leaking coolant. Seems to suggest an old air lock or the head is forcing air into the system under high load.

    Everything is telling me I have a head or gasket failure....


    Anyone (please) convince me otherwise??


    Tomorrow plan to check for air locks again as suggested while I pick up a new stat.

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    Trainee cmsmwoo1's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    swapped the stat for the cooked one that was in the engine

    cooling considerably better now (still bypassed the heating matrix - pipes entering bukhead have been joined. Also topped it completely up and removed as much air as possible again. driving well and can go up some more minor hills now without heating issues. Again up a fairly long and stepp hill the problem comes back.

    looks like my next job is the removal of the head and put a new gasket in - as luck would have it the guy next door fixes up old engines for a living and has offered to give advise and can point me in the direction of somebody to skim and pressure test the block.

    At this point still didn't rule out water pump issues but to be honest this whole thing stinks of a cracked block or makings of the complete failure of the head gasket.


    Please if any1 can concur or give me any other ideas before pulling the thing apart I'd love to hear from you! (Still got a bottom intercooler pipe split but am thinking that should just be effecting power rather than heating issues.) Also a old car nut at work has repeatedy told me to change the oil as it could cause this - not convinced but around the oild filter looks like I have a leak (amongs other minor places )

    Cheers all
    Mike

  7. #7

    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Given the age of your car the chances are the radiator is partially blocked, common problem.
    You simply can't flush it clear, new radiator.
    Are you loosing coolant at all now, if not I wouldn't worry about the head for now.
    Possible problem with water pump but I doubt it. To be absolutely certain take off and inspect impeller- they do corrode. New gasket to put it back.
    The other cause of over heating is head gasket gas leakage from cylinders, when the engine is hot are coolant hoses rock solid ie pressurised.
    Before engine gets too hot, with it running remove bung in top of thermostat housing and look at coolant, any bubbles or does coolant over flow, if either gas leakage at head gasket.
    Are you certain the viscous fan is operating correctly, although these engines run happliy without them in the circumstances worth a check.
    Hope this helps a bit

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    Engineer thebiglad's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Quote Originally Posted by cmsmwoo1 View Post
    swapped the stat for the cooked one that was in the engine

    cooling considerably better now (still bypassed the heating matrix - pipes entering bukhead have been joined. Also topped it completely up and removed as much air as possible again. driving well and can go up some more minor hills now without heating issues. Again up a fairly long and stepp hill the problem comes back.

    looks like my next job is the removal of the head and put a new gasket in - as luck would have it the guy next door fixes up old engines for a living and has offered to give advise and can point me in the direction of somebody to skim and pressure test the block.

    At this point still didn't rule out water pump issues but to be honest this whole thing stinks of a cracked block or makings of the complete failure of the head gasket.


    Please if any1 can concur or give me any other ideas before pulling the thing apart I'd love to hear from you! (Still got a bottom intercooler pipe split but am thinking that should just be effecting power rather than heating issues.) Also a old car nut at work has repeatedy told me to change the oil as it could cause this - not convinced but around the oild filter looks like I have a leak (amongs other minor places )

    Cheers all
    Mike

    Just a quick question - when you refill the coolant, do you have the heater controls on full? If you don't it won't fill properly.

    Re the radiator and overheating issues - have you checked for heat by putting your hand on different parts of it, once warmed up? If there are any areas remaining cool there is a blockage. Take the rad out and back-flush with a hosepipe.


    Re the water pump - quick way to check if it's pumping - undo the plastic plug on the thermostat housing, then get someone to start the engine while you watch. It should imediately start to spit coolant out, if it doesn't it's foobar'd.
    Had loads though!

    2010 Triumph Bonneville T100

  9. #9

    Default Re: 300Tdi periodic overheating - no hot air & no idea

    At this point still didn't rule out water pump issues but to be honest this whole thing stinks of a cracked block or makings of the complete failure of the head gasket.

    You seem hell bent on headgasket problems

    Ive changed a few for mates and mine NOT 1 with your symptons,
    you can`t compare faults on Normal cars with Disco`s
    everything goes out the window.
    Every headgasket ive done was a water port failure
    ie pistons full of water,and the same 2 (2 and 3) I have had a failure on
    3 & 4 but that was down to bad fitting (theres 2 bolts that need to be in the head before refit or dont clear scuttle so the muppet left them off.
    I suppose that some1 could have reused headbolts and this would give loss of compression,but not your symptons,
    If its not useing water its veryunlikely to be headgasket,
    Heat is generated on all vehicles and 3 forms of cooling are used to disapate it on Disco`s, Water, Air and Oil,
    Now 1 of these seem to be failing under load,
    80% of the time is useually water, then Air ,then Oil
    How long have you had the Vehicle,have you changed oil,
    does it have antifreeze in,are filters clean, is the Rad blocked externally with flys/sh1te etc,many paths before headgasket,as when a TDI gasket goes you useually know straight away,

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    Engineer ComicalEngineer's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    New radiator is your next port of call BEFORE you take the head off.
    Disco TD5 auto (Nellie)
    Disco 300tdi (Rupert) gone but not forgotten

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    Trainee cmsmwoo1's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Thanks for your all suggestions.

    Am about to remove/check the water pump tonight.

    Will add more detail later but in summary. The engine runs much better but if really stressed up hills with foot down etc. I get the temp guage rising to the red (I stop just before and with an idle it slowly moves back to middle) the stat in it was fried and I fitted the new stat with the nipple at 9 oclock not 12 so took out and adjusted. Havent ran since refitting stat properly.

    New info is:
    * overnight take off filler cap & doesn't smell great (burnt like smell).
    * immediately after a start (after leaving overnight) I can see gasses at the expansion cap which go quickly and don't come back
    * appear to be loosing water - the level in the pipes is below the water pump after running (stat is dry) after opening things up after left overnight
    * In the pipes around the stat there is a dusty brown coating.
    * flushed the system again and it's rust coloured water
    * rad flow is not perfect but flows fast


    Key is the fact that the header tank is at it's level and all the pipes which are just below bend in the pipe after the water pump (head level?) are empty of fluid.

    Will check the pump this pm and measure exactly the coolant required - fill at rad then finally at the stat housing.
    Heater matrix is completely bypassed by a bodge.
    Water loss is always occuring at the expansion cap

    Not sure if the viscous fan is fully kicking in and need to remove the rad properly tonight if time.

  12. #12

    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Just been reading your last post.
    I think you should change your engine oil possibly use a flushing oil before you do. I use flushing oil now and again, never had any bother. others disagree.
    The start up bubbles is probably you water pump mixing air into the coolant due to low coolant level. Tends to suggest pump ok.
    If you are running with no coolant in your stat housing due to loosing coolant, that is probably the cause of your temp gauge reading high. It's reading air temp in stat housing not coolant temperature. The sensor for the temp gauge is in bottom of stat housing.
    I don't think your engine is over heating - you've got a coolant leak somewhere, either at the head gasket or external. Do you blow steam out of the exhaust first thing in a morning?
    I would still change the radiator.
    You've basically got to find the leak.

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    Engineer micheal's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    could be a cracked cylinder head how much pressusre have you got im having si;malar problems with mine at the moment tested everything and replaced the water pump for a new item changed the thermostat pressurising up still but theres no smoke from the back so id say a cracked head as a possibilty
    if its not broken leave it alone
    if its stop leaking then its empty

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    Engineer bananahead's Avatar
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    Default Re: 300Tdi periodic overheating - no hot air & no idea

    If you fill your coolant and leave overnight and the level drops, you ovbiously have a leak.... just prey that it is not the leak i recently had, core plug on rear of engine below head, engine out job..... fill the system from top of thermostat housing and look underneath for leaks... i hope you dont see it leaking off the bellhousing

    Don't take life too seriously. You'll never get out of it alive.
    1998 Discovery 300TDI (Disco PEW) (staying with friends )
    1988 Range Rover Hybrid 3.5V8 EFI 88" (Boris)
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  15. #15

    Default Re: 300Tdi periodic overheating - no hot air & no idea

    Quote Originally Posted by bananahead View Post
    If you fill your coolant and leave overnight and the level drops, you ovbiously have a leak.... just prey that it is not the leak i recently had, core plug on rear of engine below head, engine out job..... fill the system from top of thermostat housing and look underneath for leaks... i hope you dont see it leaking off the bellhousing
    Just a thought,

    The thread for the plug on the thermostat housing is 1/2in bsp.
    If you were to remove the plug and screw in its place a 15mm compression straight coupling without the olive and nut on one end of the fitting, bit of ptfe tape on the threads, and the fit a short length of 15mm copper pipe into the coupling you could connect a garden hose to it. Garden hose to tap, turn on water, you will pressurise your cooling system, should show leak up with a bit of luck. Don't over do the time the tap is on or you might fill your cylinders with water if the leak is internal.
    I 've not tried this myself but it should work ok.

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