Cooling System Enquiry

[Kevin B]

Hi Fellow Landrover Owners,

When i start my Discovery (93Mod with 265,000km) from cold and start driving my Temp gauge slowly rises as it should but it goes past the halfway mark as stated in the operator manual as the correct operating temp all the way up 1-2 needle thicknesses below 3/4, never above (this takes about 10mins), once it reaches that level it rapidly goes down to halfway mark and that is were it sits only varying a needle thickness either side no matter how long i drive or weather the air temp is 20Deg or 45Deg or even how much throttle i give her, it never rises back up again during the trip, this only happens in the morning or after she has been sitting a few hours and has cooled right down, there are no coolant leaks and she runs very well, i'm not even really sure if this is a problem but it does seem peculiar as i have never had or seen a vehicle do this before, i gave a local mechanic (not a Landrover mechanic) a call and his best guess was that she is heating up to fully open the thermostat once it is fully open it settles down to normal operating temperature and that's were it stays till it cools again then it has to go through the same process next time it heats up, this does seem plausible to me, however not being to familiar with Landrover temperament i thought i would post here to see if any other owners has experienced the same thing.

your thoughts and advise would be most welcome.

P.S - she had a new thermostat replaced by the previous owner about 5000k ago, not sure if it was doing the same before that as i have only had the vehicle about 3 weeks and it has done it since then.
__________________
Regards

Kevin

[Barryp]

Sticky Thermastat, cheap to replace!
New one may have been a cheapie or faulty.
Regards
Barryp

[Kevin B]

ok yeah that makes sense, instead of slowly opening could be snapping open at a higher temp.. thanks for that

Kevin

[Blknight.aus]

I concur,

the themostat is dying most likely if it a spring jobby its been hit with corrosion or contamination and is sticking until the spring pressure drives it past the nominal point, the wavering is caused by the thermostat not closing properly untill the spring pressure reduces, it then snaps over untill the heat goes up and the whole thing cycles over and round.

Its not going to be doing your head, gaskets or head bolts any favors.

[LandyStu]

I have the exact same symptoms with my 95 disco v8:( Have tried three thermostats, QH - tridon and now another QH brand all were tested in a pot a water before fitting.
I have an Autron gauge fitted and will peak at 120c for about two seconds and then drop back to 90c. The factory gauge will follow to the top of the white zone.
I'm stumped at what is causing this.

Recently fitted 4.6 top hatted motor, ran in fine with no temp problems
Radiator cleaned and tested
New water pump
New hoses
Nulon long life coolant 50/50 mix
Vacuum filled the coolant

[bee utey]

Make sure the throttle body heater hose circuit is flowing freely. (I often disconnect the t.b. heater and run the hose direct to the rad.) A big enough flow through this hose ensures the temp sender and the back of the thermostat are at the same temperature. If the hose is blocked the temp sender will see hot water slowly drift past until it reaches the thermostat. When the thermostat finally opens a rush of cooler water passes the temp sender once the block has been flushed with the contents of the radiator. I have improved the bypass on many engines to improve the action of thermostats.