cotleigh crasher Posted April 30, 2013 Share Posted April 30, 2013 Hi Folks After changing the head on my 300tdi defender I noticed that the coolant seems to be flowing in the wrong direction. The bottom hose gets hot first and remains hotter than the top hose. I always thought that the top hose got hot first, cooled through the rad, the back to the engine via the bottom hose. I wondered whether the pump may be runing backwards but to reverse it the belt would be running with its ribbed side against a smooth pulley. I've not altered the belt run since I've had it , its always run a bit hot, at the top end of normal, just below the red. Can somone tell me which direction the pump pulley should turn, clockwise or anti clockwise? Is it normal for the bottom hose to get hot first? Anyone got a picture of the auxiliary belt run please. Ralph Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted April 30, 2013 Share Posted April 30, 2013 Sounds more like an air lock. Have you removed the various bleed screws when filling the system up? the 300's can be a sod for air locks. Quote Link to comment Share on other sites More sharing options...
Reiny Posted April 30, 2013 Share Posted April 30, 2013 As far as I know (and I may be wrong here), the bottom hose gets hot first. That's because there's no flow through the top hose until the thermostat opens. Hence, bottom hose heats up, thermostat opens, hot water flows through the top hose into the rad (getting hot in the process), gets cooled through the rad and re-enters the engine via the bottom hose. Bottom hose will remain hot to the touch. Quote Link to comment Share on other sites More sharing options...
davyd8899 Posted April 30, 2013 Share Posted April 30, 2013 i would be more worried as to why the engine is running so hot. flush the coolant with rad flush, jet wash the radiator (be carefull you dont damage it) to remove any mud and dirt, change the thermostat, then refill the coolant and run up to temp to see if its any different. as said watch for air locks. the water pump spins clockwise Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted April 30, 2013 Author Share Posted April 30, 2013 As far as I know (and I may be wrong here), the bottom hose gets hot first. That's because there's no flow through the top hose until the thermostat opens. Hence, bottom hose heats up, thermostat opens, hot water flows through the top hose into the rad (getting hot in the process), gets cooled through the rad and re-enters the engine via the bottom hose. Bottom hose will remain hot to the touch. Thanks guys This kinda makes sense, the top hose does get hot after a decent run but it never seems to get quite as hot as the bottom hose. As far as the running hot is concerned, it never enters the red, the gauge just settles a needles width below the red and stays there, quite reliably. The electric fan only kicks in on the rarest of occasions (its set on the lowest setting), usually only on a hot day after a slow run. I have changed the thermostat (with the new head) and its just the same. Something that has baffled me though, I have discovered a tiny diode like thingy in the cable from the temp sensor in the thermostat housing, its only attached by the wires twisted on and I can't imagine why it should be there. I'm wondering if its affecting the reading on the gauge. Anyone come across this sort of thing? Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted April 30, 2013 Author Share Posted April 30, 2013 Sounds more like an air lock.Have you removed the various bleed screws when filling the system up? the 300's can be a sod for air locks. Bleed screws ??? what bleed screws? I'm only aware of the filler on the thermostat housing. Quote Link to comment Share on other sites More sharing options...
davyd8899 Posted April 30, 2013 Share Posted April 30, 2013 A neadles width below the red still sounds to hot to me, unless you have a faulty guage/ temp sender, thermostat opens between 88-91 degrees , and the gushes should read on the middle, still flush the coolant system and clean the rad, see if that makes a difference. If not then I would for a different temp sender and see if you get a different fuego reading then. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted May 1, 2013 Share Posted May 1, 2013 I suspect that the diode thing is a resistor. Probably being used to modify the temp signal because the gauge was reading incorrectly. The gauge works on varying resistance and needs a matched sender to provide the correct reading. Is the 300 retro fitted or original ? Either way suspect a mismatched sender and gauge. HTH Mo Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted May 1, 2013 Author Share Posted May 1, 2013 I suspect that the diode thing is a resistor. Probably being used to modify the temp signal because the gauge was reading incorrectly. The gauge works on varying resistance and needs a matched sender to provide the correct reading. Is the 300 retro fitted or original ? Either way suspect a mismatched sender and gauge.HTH Mo The 300 is a retro-fit (it was originally a 200) so presumably there was a reading problem between the sender and gauge, this could explain the apparent hot running? Is it just a question of changing the gauge to a 300 gauge or is it more complicated than that, i.e. does the wiring need modifying? Any idea what the part number is for the correct gauge? Thanks Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted May 1, 2013 Author Share Posted May 1, 2013 A quick update: I renewed the temp sender and everything seems normal now, temp gauge reading bang in the middle. Also, bottom hose gets hot first, top hose gets hot when thermostat opens. Thanks again to you all for your advice, as usual, spot on. Ralph Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted May 2, 2013 Share Posted May 2, 2013 Glad you got it sorted. Mo Quote Link to comment Share on other sites More sharing options...
Reiny Posted May 2, 2013 Share Posted May 2, 2013 Bang in the middle is just about right, however I was recently told that Land Rover temperature gauges sit bang in the middle for any temperature between 80 and 110 degrees Centigrade. Quote Link to comment Share on other sites More sharing options...
Aragorn Posted May 2, 2013 Share Posted May 2, 2013 Cant comment specifically on the Landrover one, but factory guages "lying" to the driver is quite common. On my Audi for instance, you can connect up the diagnostic computer and it will give you the temperature from the instrument cluster specific to 1 degree, yet the gauge points directly at 90 for any temperature between ~80 and ~100c. If the temp goes out of this range, then the gauge slowly (over a few minutes) swings round to show the actual temperature. I guess the idea is that the driver should see the gauge pointing at the normal position for all normal operating temperatures, instead of seeing it rise while in traffic or similar. Personally i'd rather it just told me the truth! Then there is a trend to dumb everything down for the driver so its hardly surprising! The speedo does the same thing, What it shows on the needle is always higher than the speed reported by diagnostics. IE the cluster knows the true speed, but has been programmed to display a higher value. Once you figure that out its fine, just means you sit at "75" on the motorway to do a true 70mph, but again i'd rather it just told me what speed i was actually doing. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted May 2, 2013 Share Posted May 2, 2013 Gauges are usually non linear to stop the general public becoming alarmed by changes in temperature which would be quite normal, thermostat opening/closing etc. Same is true for fuel tanks, the first quarter always takes longer to go away and then it drops faster, because people don't like to see their just-purchased tank of fuel disappearing right away! Speedos are always over because they are not allowed to under-read, but are allowed to over-read by a small amount (10% or something I think) so the manufacturers err on the side of caution. Plus it makes people think their car is faster than it is, which is good for selling the things. Like Aragorn I would personally prefer to know the true figures, but not enough to make me want to put ugly after-market gauges in. I have however managed to find an old 80s VDO temperature gauge that is a nice match for the standard Land Rover Td5 temperature gauge (better match than the modern VDO Vision range) so I will be swapping that in when I get a chance Quote Link to comment Share on other sites More sharing options...
ejparrott Posted May 2, 2013 Share Posted May 2, 2013 +1 for the true figures..... Its a real cause of road rage for me that we drive for miles and miles up the M6 at 45mph throught he 50mph speed limit, because other people speedos are (in mu opinion) wrong! I have the sat nav, and drive at bang on 50.....when the ejits get out the way of course.... Quote Link to comment Share on other sites More sharing options...
davyd8899 Posted May 2, 2013 Share Posted May 2, 2013 +1 for the true figures.....Its a real cause of road rage for me that we drive for miles and miles up the M6 at 45mph throught he 50mph speed limit, because other people speedos are (in mu opinion) wrong! I have the sat nav, and drive at bang on 50.....when the ejits get out the way of course.... i second that, a real case of ignorance is bliss, ignorant people that dont know about the speedo or the rear view mirror.... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.