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[ians]

I drove into London on Saturday (a mistake I make about once a year..).   Quite warm weather and large amount of traffic jams.

The running temp in the 3.0 is usually around 95 - 97, but gradually rose over about half an hour to >100 on the guage.   (I switched off at that point)

I know the fan (at least one of them) is working as it runs on for a couple of minutes after switching off, but I wasn't in a position at the time to hop out and check if it was going full blast (they are 2 speed, aren't they?).

In my old 2L when the temp got up to 98 or so in traffic, the fan would come on and the temp would come down very quickly - but this doesn't seem to be happening.

Any suggestions?

Cheers
Ian

[TheBoy]

Assuming the instrument panel is configured right, you need to sort out cooling - cruising shouldn't need the fans.

[Kevin Wood]

I also drove through London on Saturday and it got my blood pressure rising a little never mind engine temperature. Poor old Tom Tom nearly hit the tarmac for taking me round the S. Circular.  

I would be inclined to wait for a nice hot day, let it run up from cold to as hot as it's going to get and give it a few checks.

Start from cold
Does the top rad hose stay cool until up to "normal" running temperature then get very hot?
Does the fan come on after another couple of minutes?
Does the bottom rad hose get rather warm by this point? Should be almost as hot as the top hose.
If you can get to the back of the rad see if it is warm all over (or use an IR heat gun to measure temperature, looking for "cold spots").

If you can't get onto the second stage of the fan try blocking the airflow through the rad to see if it kicks in or short the contacts on the thermal switch to test operation of the relays and motors.

Try the fans with air con both on and off, as the motors are switched differently with air con running.

It's not necessarily a problem to run at 100 deg. c. Some production cars run the coolant at or above 100 as standard these days. It shouldn't boil until 115-120 deg. C with a proper coolant concentration and working header tank cap.

I think possible problems are as follows:

Rad. Fan Thermal switch or relay issue.
Lazy thermostat (not opening fully)
Blocked / silted up radiator
Possibly knackered impeller on the water pump.

Sounds to me like it was basically holding its' own but efficiency is not as good as it should be. However, if it normally runs at 95, it will probably be up to 100 before the fans start, and on a hot day in traffic, it's normal for it to sit at the temperature regulated by the fan switch.

Kevin

[TheBoy]

It's not necessarily a problem to run at 100 deg. c. Some production cars run the coolant at or above 100 as standard these days. It shouldn't boil until 115-120 deg. C with a proper coolant concentration and working header tank cap.
Kevin

Only what the gauge reads and reality are considerably different around this area of gauge....

[Kevin Wood]

Only what the gauge reads and reality are considerably different around this area of gauge....

True. Always take the gauge with a pinch of salt. Relatively speaking, though, if we're talking about it running "a tad" (5 degrees) hotter than "normal" I wouldn't regard that as a surprise in heavy traffic in summer, assuming "normal" is OK, of course.

I don't know why they mark the gauges with temperatures when they bear no relation to reality.

Mrs. KW's MX-5 reads dead on the centre of the gauge from about 1 mile after a cold start to just before it pops its' rad cap. On inspection, the gauge is driven from an output on the engine ECU so it has been "engineered" to remove any fluctuation of the gauge until it's about to blow up.

It also has an oil pressure gauge that's driven by a conventional pressure switch - so it has 2 positions: 3/4 scale and zero.

Kevin

[TheBoy]

Only what the gauge reads and reality are considerably different around this area of gauge....

True. Always take the gauge with a pinch of salt. Relatively speaking, though, if we're talking about it running "a tad" (5 degrees) hotter than "normal" I wouldn't regard that as a surprise in heavy traffic in summer, assuming "normal" is OK, of course.

I don't know why they mark the gauges with temperatures when they bear no relation to reality.

Mrs. KW's MX-5 reads dead on the centre of the gauge from about 1 mile after a cold start to just before it pops its' rad cap. On inspection, the gauge is driven from an output on the engine ECU so it has been "engineered" to remove any fluctuation of the gauge until it's about to blow up.

It also has an oil pressure gauge that's driven by a conventional pressure switch - so it has 2 positions: 3/4 scale and zero.

Kevin

Vauxhall aren't as bad as some (BMW being a big contender here), but still 'modify' the value significantly.  Tractor is 10C over when gauge reads 97C.  MV6 looking to be not too dissimilar, going by readings on both at around the 96C mark (both reaching 100C)...

[ians]

Thanks Kevin, TB.

I understand the absolute numbers are fairly meaningless but I didn't feel comfortable with it nearing the top of the scale - esp as I recall TB saying previously that there was a significant error in the reading at higher temps.   and I lost my bottle when the warning light came on, so I parked up for a while.

Can you remind me where the thermal switch sits?  If I short it out should that kick the fan into full speed?   There seems to be one big

Cambelt is due soon and I will do the water pump at the same time - I did wonder if the pump could lose efficiency..  I suspect its the original 135k old.   I will probably do the stat at the same time as the plenum is coming off anyway.

I did flush the coolant system 6 months ago - can't say any crud came out and it has 50% fresh mix in now.    

Cheers

Ian

[Kevin Wood]

IIRC, the switch is the one on the rad. just below the top hose.

Have a look at the wiring diagrams and you'll see it has a 2 stage switch. Try shorting one then both and it should behave as follows, from memory:

Air con off

1st stage:
Rear Radiator fan on half speed

2nd stage:

Rear radiator on full speed, front radiator fans on

Air con on:

Front fans on half speed constantly

1st stage:
Rear Radiator fan on half speed

2nd stage:

Rear radiator on full speed, front radiator fans on full speed

Also worth checking the fuses in the engine bay relay box.

If the light came on then it was getting hotter than it should.

Kevin

[ians]

Thanks Kevin,

Is the light fed from the guage or an independent sensor do you know?

[Kevin Wood]

Thanks Kevin,

Is the light fed from the guage or an independent sensor do you know?

I believe it's from the same gauge sensor. The logic in the dash switches it on above a certain indication from the sensor.

Kevin

[tmx]

In hot weather my 3.0 runs at 95 and in the cold its at 90"c it gets to 100 if i leave it parked in the sun and nip into the shop for 5 mins but soon gets back down to 95

[Mike Collins]

An earlier 2.5 I had started to run very hot, fans on almost continuously.

After a lot of fiddling about and changing pump and thermostat, I took the radiator out and had it flow tested. Blocked, recored and refitted, straight back to halfway up the temperature gauge.

I don't think the pump can lose effectiveness, its a very crude looking metal paddle arrangement.