Unusual engine cooling fault NOW FIXED ! (27/1/2010)

UPDATE UPDATE UPDATE UPDATE 27 January 2010....

see below....! see below !.... see below ...! see below.....!

The temp gauge has dropped to zero when cruising at 60 mph after about an hour from start up... Never seemed to rise to "normal" position.... I slowed down, to see if it was related to the speed of cold air (it was freezing weather) through the radiator, but did not rise significantly....

got home and replaced the thermostat with new one.... ran engine, took about 30 mins to get up to "normal" temp.... with the cap off the reservoir, revved the engine a couple of times and then put the cap on tight, whilst engine running.... went for a "test drive" the needle gradually dropped back to zero, checked coolant level, remains at normal....

is there any other way to "bleed" the cooling system???

1. Water seems to be circulating, as it looks like it is being pumped into the reservoir by the small bore pipe at the top of the engine to the reservoir.... (so am assuming the water pump is ok..... confirm diagnosis ..... yes or no???)

2. Performance does not seem to be affected.....No excess smoke or pressure in oil filler ...rad hoses do not seem to be "pressurised"...... no loss of coolant....... (assuming head gasket must be ok...... confirm diagnosis ...... yes or no????)

3. Temp gauge needle moves.... (assume no fault with gauge...... confirm diagnosis..... yes or no???)

4. When the temp guage is showing zero (cold) the bottom of the rad is "cold" to touch, when temp gauge shows "normal" (after standing still but running engine to get hot)... the bottom of rad (and bottom hose (where thermostat enters engine block to bottom of rad) is hot.... (as would be expected with correct operation of thermostat).....

5. No warning lights appear on dash board !

Any advice would be appreciated.... thanks

Gerry

EDIT EDIT EDIT EDIT EDIT EDIT

OK.... so I have replaced the thermostat...... and I have now replaced the Temperature sender unit...... but the problem is still the same....

further info.....

the heater is working..... but only Warm Air, is coming out.....

the top hose from the engine to the Radiator is "comfortably warm".....

the "bottom hose from the side of the engine (with thermostat in at engine) is "cool".... bottom of rad is "cool".... (not COLD.... cool! )

Road testing for 30 minutes does not bring the temp gauge to move..... but 30 mins after that, at tick-over standing still, the temp gauge will reach Normal..... then on a road test for 15 minutes, the gauge will gradually return to the cold positon, despite the heater still blowing (gently) warm air......(No loss of performance durng road tests)

UPDATE UPDATE UPDATE UPDATE UPDATE

OK... temp gauge is now working properly....... !....

got myself ANOTHER NEW THERMOSTAT..... fitted it............... ran engine for 10 mins, then put coolant reservoir cap on,............ went for a drive.......10 mins up the road, and the temp gauge was climbing............. another 10 mins............ up to normal position......... stopped car, checked coolant level...... seemed to have lost about half a litre..........(did a quick check for leaks but none found ) ..... topped it up, and drove home........... temp gauge remained at normal........... at home............ checked coolant level........... NORMAL !.....

Been in and out on short journeys all day, and everything seems back to normal now..... oh yes, my heater works REALLY WELL now.... !....

(took the old "new" thermostat back to the shop, and got a refund on it.)

Not sure if this is significant. BUT..... original did not have any holes in the plate of the thermostat....... the old "new" one did !.... the NEW new one (the one that is in now), does not have any holes in it..... (both new one`s were made by Quinton Hazel)l.... retail...... (from motor factors) at £12.84.....

I used to sell the very same item 25 years ago for little over £1 .! ! ! :'(

Moral of the story is.... if you think it might be , then it probably is ! ! !....

Edited 27 January, 201016 yr by Skodadriver