over heating on idle

[yeah_mick]

last night my car went all the way upto the red after idleing for about 10-15 minutes, but when driving it sits nicely between a quater and half on the temp gauge. is this common? what could be causing this? rad looks to be in good condition, no coolant leaks.

[MJJ_ZX6RR]

If you've not done anything to the cooling system recently to introduce air into the system, I would suspect the viscous clutch for the cooling fan.

Martin.

[yeah_mick]

how can i check this??

ive just had a drive of the car and at low speeds it creeps up to about 3/4 but on dual carriageways it sits bang on half, when i stopped i had a feel of the rad and pipes, the top pipes were hot and so was the top corner ofd the rad, but the bottom pipe was only mildly warm as was the majority of the rad. could this be a knackered pump? rad?

[MJJ_ZX6RR]

Mick,

I think your whole colling system needs some love.

- Rad not uniformly hot suggests it is blocked. Some rad flush may help, but I think a new rad (~£130) from GSF or adrad.co.uk would be a wise move.

- Temp is OK at speed, but overheats when stationary is likely the viscous clutch. To test it, you need to *carefully* try to slow the fan down when the engine is nice and hot. The fan should spin all the time, cold or hot, but the clutch should engage when the engine is hot and spin the fan harder and faster. Use a rolled up newspaper for example, and see if you can slow the fan down. If you can easily, the viscous clutch needs replacing (part is ~£30 IIRC).

- Temp gauge varying between a quarter and half on the dual carriageways suggests the thermostat (~£25 IIRC) is also partially stuck open. It should sit bang on half and not move with a healthy cooling system.


Martin.

[DHFiS]

Open the bonnet. If the coupling is working and you rev the engine when its hot you can feel (and on mine hear) the blast of air.

[BillyW]

Mick,



- Temp gauge varying between a quarter and half on the dual carriageways suggests the thermostat (~£25 IIRC) is also partially stuck open. It should sit bang on half and not move with a healthy cooling system.


Martin.

Mine sits on quarter most of the time with the heater on full blast but creeps up to half in traffic, i only changed the stat last month.

[zaust]

Agreed with the thromo, +

Have you done the news paper test to see if you fan is working or not ???

(Roll up a paper and see if the fan stops or shreds the paper at over half on the gage.)

[yeah_mick]

i wont be driving it again until tomorrow so i will get the news paper out then. zaust you can have a look sunday if you like

[yeah_mick]

after dirving my car again, the temp gauge kept going up and down, but when it went up the heaters went stone cold, also it was at about 3/4 when i got back so i got out a newspaper and touched the fan and it stopped really easily. ive been told these are heat opperated so they know when the engine is at running temperature and what now, will this have anything to do with the thermostat? im going to chuck a new one in anyways but just wondering.

[HJG-E30]

surely the bottom rad hose only being mildly hot is a good thing, as it shows the rad/fan have at least been cooling the water?

[johnt0709]

sounds like an airlock or thermostat to me

[yeah_mick]

but its too cold, more like just warmed from the heat in the bay, so it seems as though water isnt getting round, im going to pick up a thermostat in a bit and ill get that fitted tomorrow hopefully before work and then i can test it out and see how that goes. if the problem is still there then i guess ill hvae to flush the system and change the fan coupling

[Banjo1981]

It's probably a thermostat being stuck closed or partially closed that's causing this.

Basically, the engine warms the water jacket and as it reaches temp it allows water to circulate through the rest of the system (rad and heater matrix). With a closed or partially closed 'stat the water isn't leaving the engine to cool in the rest of the system.

The cooling is caused when air flows over the engine whilst driving, partially cooling the water.

Don't drive it as you could risk major damage to the engine as I did with a landy several years ago, it was an expensive lesson to learn.

[town325i]

It's probably a thermostat being stuck closed or partially closed that's causing this.

Basically, the engine warms the water jacket and as it reaches temp it allows water to circulate through the rest of the system (rad and heater matrix). With a closed or partially closed 'stat the water isn't leaving the engine to cool in the rest of the system.

The cooling is caused when air flows over the engine whilst driving, partially cooling the water.

Don't drive it as you could risk major damage to the engine as I did with a landy several years ago, it was an expensive lesson to learn.

if the temp gauge os up and down it can mean that the water pump is on the way out if its and M40 engine it could have a plastic impellor type water pump that has worked its way loose and stops and starts causing the temp gauge to go up and down

[yeah_mick]

little update, i went to change my thermostat and snapped one of the bolts holding the cover on the housing and another one felt like it was going to snap so i stopped for the time being, but when i took the top rad hose off no water ome out and it took aboout 1.5litres to fill it all back up again, after that its running at about 1/4 whilst moving but in the time it took me to fill the car with fuel it rose to 3/4.

what i want to know is how hard is the thermostat housing to change? i have access to a spare engine with everything on it (dont tell si i said this)

[town325i]

what engine is it? buy this im guessing M40

[yeah_mick]

Should have said in the first post its a M20b25

[HJG-E30]

it' s common for these to snap. one of mine sheared but luckily it was the top one and nothing leaks from it, as the other two are nice and tight. Use some penetrating fluid and a 6pt socket. Try tightening it a little first and then loosen it. You may have to repeat this procedure a few times.