Hi,

It sounds to me like 1 of 2 things. Firstly it could be the water pump. As I understand it, a lot of them had plastic impellers that would eventually over time loose grip on the shaft. So whilst the engine was going faster the coolant wasn’t which leads to quick over heating. The second thing it could be is the thermostat. Which is failing to open correctly and not allowing a sufficient flow of water through the radiator.

As a precaution for any car that has over heated, it is always wise to change the thermostat as they can loose there efficiency after being toasted.

As for the bleed screw, there only a few pence from the local dealers. I wouldn’t be too confident on blaming it all on that though as it may have been damaged when the car over heated. The hissing sound your hearing is most likely air/water escaping from the expansion cap, as to not let the system get so pressurized it blows a hose off!!

Hope that helps a bit

IMO it is definately the bleed screw. All coolant systems work under pressure. If the system cannot pressurise, the water will boil. If the screw wasn't a good fit then the pressure would have finally got to it as the housing is only alloy. You said you were also losing coolant at the bleed screw, that just adds to the problem with less water in the system causing air locks and with the hot weather, it all adds up. You may need to drill the housing and use a bigger screw if the hole is no longer round.

I would start with obvious bad screw and make sure you bleed the system fully when filling back up and watch the gauge and more than three quarters it's overheating. You need to be real careful 'cause the alloy head on the small six is prone to warping or cracking if it overheats too much then it's an expensive fix!!

Rob

I can see on the screw that some ridges are worn im not sure but dont the screws come in one size or can you get bigger ones, also if the new one dont fit what would you advise me to do then.

Skanders,

pretty hard to work out with what you have detailed. You can remove the thermostat for these tests to rule it out by the way.  It does sound like the system has an airlock though.When you refilled the coolant and then started the car, was the heater on hot with the blower on and then you released the trapped air through the bleed screw until only fluid escapes, and the heater is blowing hot? Then top up.

You mentioned about smoke and a whining noise now? The noise sounds potentially like the viscous coupling on the fan (known failure point) , or potentially the pump bearing, no idea on the smoke tho unless something is burning in the heat.

Rob

Get a new water pump mate. It defiantly sounds like that's too blame

Get a new stat aswell just to be on the safe side. Go to somewhere like GSF or ECP for the pump. Should only be around £40 IIRC

The way I bleed the system is as korky has said above but run engine with the bleed screw loosened and the cap off from cold, heater on hot and keep adding water while raising the rpm a little to raise the water pressure till there is no more air escaping from the bleed screw, only water. This can sometimes take quite a while. Once there is no air escaping, lock off the screw then raise the revs to about 3k and run like that for a minute just to let the water pressure force out any other air, watching the temp gauge of course, and return to idle and then loosen the screw again to check for air. If you do it straight from hot the water will expand so when it cools down again the level will not be correct and can sometimes draw air back into the system.

Rob

The Thermostat simply controls the amount of water that flows through the radiator to keep the ideal operational temp.

So it is fully closed when the engine is cold so it can heat up quickly and gradually opens up to allow the coolant in the block to flow round the radiator. It will open and close at varying degrees depending on speed, engine rpm, and ambient temp to keep the temp gauge bang in the middle.

Sounds like in your case it just wasn’t opening enough. A word of advice, get a new one from the dealers as there a lot better and more reliable than the aftermarket ones you would get in halfords or somewhere similar!

P.s. when you looked at your water pump did it have a plastic or metal impeller?

Should be OK to run without the thermostat as a temporary measure. It will just take a long time to heat up and wont be running at its peek operating temp. Certainly no danger of over heating!

Seriously though, I would really consider changing your water pump for a metal impeller one. There a well known failer point. but its up to you...

Hi guys while coming to work the car was fine temp gauge slap bang in the middle on the motorway but when i hit traffic and came to a standstill the car started to overheat again.

But this time instead of overheating while accelerating it cools down the faster i go it cools itself off.

Any ideas to what it could be definately the thermostat is shot so i have ordered a new one do you think that the fan may need replacing as well as i only think that this is causing the fault now.

please advice the car runs perfect so it cant be the head gasket.

thanks.

Did the fan test rolled up a bit of news paper and put it in the fan it did not shred it the paper jus flapped about and stopped the fan.

I think im gonna go with a new coupling which i think will finally put the overheating issue to rest.

thanks.

After looking through some of the replies I would deffo say get a new water pump with a metal impeller, although yours may look new it will not last long. For the sake of £31 is is worth a bill for £100's not for changing it while you change the thermostat, although it is your choice. I had a lot of problems around christmas with over heating and I ended up changing water pump thermostat, housing and seals, just for peace of mind and I know that mine will now be trouble free for a while. But its your choice.

Can be almost 100% certain that the viscous coupling on the fan is not working correctly. When the air travelling through the radiator is at a certain temp the coupling stiffens up to drive the fan, when cooler it eases the grip, almost like a heat variable clutch. If, when the water is hot the fan will not shred a paper or you can stop the fan with it, the coupling is shot and a new one is required. If you have a plastic impeller on the pump then definately replace as they are prone to failure, usually at speed.

Rob

Hi,

After 20 years of owning Bm's went to Mercedes, now back on right track.

Sorry to intrude, you have a few small problems here:

You have fixed the bleed screw. So now the system pressurises as it should. You remove the termostat. So, all the coolant will be at the mercy of the elements. So, if you get stuck in traffic, even with a new coupling on your fan, at idle the car will not cool itself down enough. Some people raise the revs (2000 is enough) as an emergency measure and car cools down a little.At 70mph on a winters day the car will be running very cold, in the blue really.

Answer, new termostat asap. They are dirt cheap. Second, new water pump. You have stated it is the plastic type. With age they don't only desintegrate but with heath they stop turning with the shaft, ie the shaft turns ok but the plastic has expanded so it stays still. And you overheath.

For its cost, new fan clutch or viscous coupling. And lastly, make sure there are no air locks at all. Bleedin explained before. Okok so its £100 spent and a mornings work, a new head will be 7 times that.

There is no point in cutting corners, thermostats go, the water pump was a design fault and bmw corrected it, the viscous fan degradates after 60k give or take.

I hope this helps, Antonio

Hi,

Thanks for your advice antonio I have the new thermostat and the new coupling it will be installed tomorrow and then i will go ahead and get a new waterpump as well.

I have not had a lot of luck with this car its great but since i bought it in march ive had the shocks, brakes, bumper (cos i broke it), door handle (interior), bleed screw, door panel fixed.

And now the thermostat, coupling and need a new tyre and need to fix one of the wipers cos i broke it tightening the screw too much but am gonna try and fix it if i can or get a new arm and lost ma left fog light cos it fell out.

So DOH! so far but the car itself as in driving experience has been beautiful and i still love it but jus had a bit of bad luck.

Oh well it can be fixed or should i off it what would you do in my shoes.

Hi Simple......years ago I had a E30 M3

To cut story short, new chain, new main bearings, new wiper mechanisnm, new seat, new brakes all around, new........everything. And Years later.....I miss that car like mad. Had a cosworth mercedes, a 911, alpina's etc. But THAT car..... I want it back.

In short, ALL cars will go at some time. A lot needs doing all at once. If its a renault etc it will carry on, if a proper car like yours, chances are after a wile it will stop and will carry on. My 3.0 csl has done so. evry 5 years needs 2k spent. And the old 750 as well. But for the next 5 years its spot on all the time. My old 500 sec is the same. Every 6 years a few major things come along. But it was a 80k car to start with. If you were the original owner, would you cre for a 3 k  service....... same principle applies I think. Good luck , take care, A

Yeh fair enough you are right at some point things are gonna need mending even human beings break down for crying out loud then again its better that they all come along at once rather than one at a time.

Anyway I love the thing I dont think I will sell it until it gets to about 160k its at 103k at the mo so a long way to go.

Anyway I should have it all done by friday.

PS:- is there anywhere i can post pictures of it.

thanks.

The needle on mine only does just over the half way mark but never moves. I take it this is normal but I may be corrected.

Well guys it was fine when fixed yday but while going to work it started to overheat again went all the way into the red so i had to pull over.

Theres no hot air blowing through the heaters my dad seems to think that it seems to be sucking up air somehow.

Any advice guys could it be head gasket, but when thermostat is not in the car it seems fine.

Also is there any particular way the thermostat needs to be in the car as I hav put it in diagonally in the 11.25 position can it start to overheat if it is in the wrong position.

Please help.

Cheers.

Yeh thats what happens when the car is running and the needle in the middle, steam and small spittles of water does come out of the bleed hole and continues to come out and never ends basically, I would like to know what i should do with this leave it running until it ends ?.

Also the thermostat has been put in diagonally should i put it so that the bleed hole is pointing up.

Could any small pin holes in the pipes cause this.

Can too much water be an issue as it is way over the cold mark.

I know that when the thermostat is not in the car there is warm air coming out of the heaters when they are on.

But when it is in the heaters blow cold air and no warm air and then it overheats after about 3 miles or so but have noticed that when going up hill it cools.

The system has been bled and bled over and over again with no luck.

Could anyone please answer my questions i know there has been a lot but i am looking for a resolution to the problem i dont want to pay a garage £££££ for an airlock if it is that cos some garages will make it up for the £££££££.

cheers gents appreciate it.