M42 running really hot after replacing thermostat

[MrT8064]

bear in mind with the over heating thing because of the front end on an E30 being the way it is, and its almost mustang like front grill its practicly air cooled when driving along at a decent speed

That's sort of why I was wondering if the fan could be causing over heating at lower speeds and higher revs.

When I talk about going up hills I mean 20mph, 2nd gear, 4,000 rpm type hills.

With a broken fan, would you expect the cruising temperature to be at the bang on middle, or slightly above as i've experienced?

[MrT8064]

BTW, an electric fan still places load on the engine - the power making the fan go round comes from the alternator...

I get you. I thought that it being directly connected may be worse than it being powered from the alternator. Guess not!

[jmc330i]

When I talk about going up hills I mean 20mph, 2nd gear, 4,000 rpm type hills.

With a broken fan, would you expect the cruising temperature to be at the bang on middle, or slightly above as i've experienced?

The heat will rise at that speed and rpm. The engine is working hard to pull the car up the hill, there won't be much airflow at that speed and 4k rpm will produce a lot of heat. This weather won't be helping either.
My M40 rises to over 3/4 going up hill at 40mph in this weather, revving around 4k-5k rpm - mine has a new rad, water pump etc.

A knackered viscous will only affect the temp while on the move if its locked up. I think once travelling at speed, the airflow over powers the viscous so the blades spin faster than the clutch so they can't restrict the airflow.

As Grrr and I have said, rads are service items. Get it changed, you won't loose anything changing the viscous either.

[MrT8064]

My M40 rises to over 3/4 going up hill at 40mph in this weather, revving around 4k-5k rpm - mine has a new rad, water pump etc.

.....

As Grrr and I have said, rads are service items. Get it changed, you won't loose anything changing the viscous either.

I wonder if thats typical of the M42 as well then.

Looks like i'd better change the rad then. By the looks of the bleeding valve the radiator hasn't been changed for a while:

[MrT8064]

Well I'm about to get a radiator ordered. Does £67.20 from Carpart4less sound good? I can't think of anywhere cheaper!

Thanks

[Andyboy]

Does the heater blow hot air? If it does, it's bled. Circoli thermostats.... Hmmmm. Cheap aftermarket stuff. Whip it out and dunk it in a pan of water on the hob to see if it opens fully when approaching boiling. Could be a knackered rad but don't pay iS tax because the rad is the same as the E34 520i and 525i and cheap new. If it's not pissing steam and dumping boiling coolant it's not a disaster but M42's do not like being overheated. A cracked head will result.

[MrT8064]

I took the thermostat out this afternoon and put it in a pan of water. It seemed to open up fine, though it was pretty slow - I guess this is normal.

I also took the radiator out and gave the internals a good spray with the hose pipe, lots of orange gunk came out but the performance doesn't seem to have improved.

Whenever i've been bleeding it I have been getting nice hot air, so nice to know i've been doing this right.

I think the radiator really is the next port of call. I've not let the temperature get into the red yet so hopefully the head is still fine!

Thanks!

[Andyboy]

The brown gunk is rust from the block, meaning it's been run without antifreeze for some time. The rad doesn't look that old. I'd refill the cooling system with some limescale remover (the stuff used in washing machines) and run it on that for a couple of hours to clean it all out.

[MrT8064]

Thanks for the suggestion! I've removed the radiator again and put it flat on a table with a couple of limescale tablets in to work away for the next hour or so.

Is it totally safe to just add a couple of dissolved tablets into the water system? - They're pretty fizzy so I thought i'd better double check before sending that stuff around the engine block!

[Brianmoooore]

It's not just the radiator that needs a descale if its been run without antifreeze. The block and head will need it as well. Get down to a plumber's merchant and get yourself some central heating cleaner, run it in the engine for a couple of hours, then take the rad. out again and thoroughly flush both the rad. and the engine with clean water from a hose.
Disconnect one of the heater hoses from the bulkhead to help with the flushing, but don't force water through the heater from the top stub. to the bottom stub. - only flow it upwards.

[MrT8064]

Thanks for the advice, I'll give the whole engine a good descale tomorrow. My efforts solely on the radiator seemed to make no difference.

I don't think I had mentioned before, but having the heater on full blast hot in the car makes a big difference to the temperature gauge. The moment I get any sign of over heating, I pop the heater on and this seems to stop it going too crazy (but doesn't bring it down to the mid point really).

When you talk about flushing, Do you mean detach the cold flow pipe going into the thermostat housing, and fill flush downwards from there?

[harry_p]

No, the air coming through the front o the car at 70mph is far more than the fan will ever shift.

Has the car ever ha a replacement radiator?

If the cars just getting hot, but not over pressurising the systems or causing air locks then the most likely cause of running hot is a partially blocked radiator.

The fan is only there to control temperature at low speed. Above about 20mph its the flow caused by movement of the car, the radiator and the thermostat.

[MrT8064]

Hmm I put my hand on the radiator after a 15 minute drive... and here is what I found:



My assumption would be that the bottom right SHOULD be colder than the bottom left.

[harry_p]

Whoops, didn't realise the topic had a second page

[MrT8064]

Perhaps you can shed some light on my radiator picture then?

[harry_p]

I would still suggest a new rad.

After 15 mins or so on a warm day I would expect the thermostat to be fully open, and all of the radiator to be hot.

Also with bearing in mind that the viscous fan won't lock up unless there's hot air flowing over the front of it, which isn't going to happen unless the radiator is heating up properly, and is another reason why the fan shroud needs to be in place.

[MrT8064]

Ok. So a radiator should be fully hot all over after a decent drive? - It shouldn't feel noticeably colder in any area?

Also from recollection i'd say my thermostat opened about 7-8mm when I put it in a pan of water... is this normal? Thanks harry_p!

[harry_p]

You'd expect the bottom to be a little cooler than the top, but not one area roasting hot and another stone cold.

How was it with no thermostat? Did it ever start to get hot even at high load for a long period?

There is a chance that the thermostat isn't reacting quickly enough to increase flow through the radiator.

Personally I've not had much luck with circoil thermostats, on two ( non - bmw ) cars I've fitted them to neither has fitted properly ( ive had to reuse the old seals )

If it didnt ever overheat before putting a thermostat in I'd be tempted to try a different thermostat before spending out on a radiator. Even a known good secondhand one from a friendly zoner would be worth a try.

[MrT8064]

How was it with no thermostat? Did it ever start to get hot even at high load for a long period?

With no thermostat it would usually sit just above the blue marker, but occasionally rise above the mid-point after lots of speedy driving.

I did think the o-ring on the Circolli was not an extremely tight fit - perhaps I should start by ordering a new O-ring - Think they are about 90p on ECP.

[Brianmoooore]

Has the water pump been checked/changed on this car?

[MrT8064]

Not been changed, but when I rev with the bleeder valve open water certainly comes out at quite a rate!

[Brianmoooore]

All your symptoms would be explained by a pump with a loose or mostly disintegrated rotor.

[MrT8064]

Right, well i've braved the weather and taken the water pump out. This photo is of the worst side of the impeller - the other side looks less pitted.

It doesn't look too bad to me compared with others i've seen floating around the web. Do you think its still worth changing over to a new unit?

Thanks!

[Brianmoooore]

Looks OK from here, but since it's out, I'd change it anyway.

[MrT8064]

New water-pump in, and sadly the problem is still there.

After a 15 minute drive the lower radiator hose (bottom right) still felt pretty cold. I'm thinking this thermostat might just be dud as someone suggested earlier!

UPDATE:

I took the thermostat out (again!!) and put it in a pan of water with a meat thermometer. It didn't even start to open until it got to about 94 degrees, then wasn't open wide until even nearer boiling point - Opening extremely slowly.

I'm going to run the car with no thermostat until a new one arrives

[MrT8064]

Just updating again. New thermostat arrived, this time I installed it with a correct gasket rather than the instant paste.
Sadly there was no big improvement, the dial sat fractionally lower but that may have just been the weather!

After a good run the bottom left of the radiator was stone cold still - even after flushing with radflush.
I checked a friends identical radiator and the bottom left was really hot. So that hopefully goes to confirm that the radiator really has gone.

I ordered a new one from carparts4less for £67, plus 5L of concentrated antifreeze for £12. They have a £10 off promotion on at the moment too, so that got me both for a shade under £70!

I'll report back once the new rad arrives and gets installed

[Brianmoooore]

but that may have just been the weather!

Weather, or even how hard you are using the engine (or not) should have no effect on the position of the gauge needle on any car. Any variation indicates a faulty or inadequate cooling system.
The only time the needle should rear anything other than normal, after the car is up to temperature, is if you turn the ignition back on a minute or so after stopping it, when the needle should read slightly higher. This should return to normal in several seconds after the car is started and the water pump starts moving things again.