Curious Overheating/Bleeding Issue Following Head Rebuild

[tyrehit]

I've recently re-fitted the head to my '88 325 after the head gasket failed due to an as-yet unknown cause. It all went back together fine but the engine is overheating immediately (when left idling it carries on past the middle of the gauge - I haven't driven it at all).

When filling the cooling system I:
- pulled the hose which runs from the head to the heater off the head then filled from the header tank until water came out of the hose - i.e. water runs through the heater OK
- filled the radiator through the hose that connects it to the thermostat (until water came out of the bleed valve on the thermostat) - i.e. radiator isn't blocked
- removed the brown gauge sender and filled through this until water came out of the back of the head
- topped up through the header tank

Thermostat has been checked in a pan of hot water, however I've now replaced this with a thermostat which is permanently open (for testing).

The hose to the top of the radiator gets very warm but I think this is just conducted from the thermostat - the top of the radiator is cold.

When the temperature rises there is a screeching noise coming from the water pump/front of engine area so I have replaced the water pump with a brand new one (although the old one actually seemed fine) but the noise happens with this one as well.

Have I missed anything obvious? Any thoughts?

Cheers!

[e30_Turbo]

I've always made sure the heaters are on full hot and blow and also jacked the front of the car to avoid air locks in the heater matrix. Filling through the top rad hose too.

But I've always had fun getting coolant back in after a head swap or infact any time where the coolant has been drained fully.

HTH, Mark.

[Gt6s]

You might have an air lock.
But.
Have you back flushed the radiator ?
If you had a cooling system full of chicken soup, This stuff can block the core of the rad very sucessfully.
Remove rad, leave short rubber bottom hose on rad connect this hose onto a good pressure large bore mains tap.
You should have a real good flow through rad

[tyrehit]

I've always made sure the heaters are on full hot and blow and also jacked the front of the car to avoid air locks in the heater matrix. Filling through the top rad hose too.

The heater was on full heat but the fan was on 0 - will give that a go this evening. However, I did try pulling off the top heater hose (which goes to the header tank) while the engine was running and coolant came out which suggests flow through the head and through the heater

But I've always had fun getting coolant back in after a head swap or infact any time where the coolant has been drained fully.

Yeah - everyone has been telling me that!

Have you back flushed the radiator ?
If you had a cooling system full of chicken soup, This stuff can block the core of the rad very sucessfully.
Remove rad, leave short rubber bottom hose on rad connect this hose onto a good pressure large bore mains tap.
You should have a real good flow through rad

I haven't put a hose on it but I did pour in a few litres of water and it came out the bottom pretty quickly. Also, I filled the radiator hose until water came out of the bleed valve on the thermostat which suggests flow, though admittedly not how quickly it can flow. Will try a hose this evening.

[klobuznik]

¿Did u get all the possible air out of the system?

Unscrew a littele bit , number 8 on the graph, with the engine running and let all the air to get out....



Check also the Visco of the Ventilator...

If u have AC, u have to check also if the auxiliar electrical ventilator runs ok at temp of 91ºC & 98ºC

[alackofspeed]

The hose to the top of the radiator gets very warm but I think this is just conducted from the thermostat - the top of the radiator is cold.

Only hot close to the thermostat housing, or along the whole length?

[tyrehit]

Unscrew a littele bit , number 8 on the graph, with the engine running and let all the air to get out....

I did this but the temperature rose too quickly and I had to turn it off before it overheated.

Check also the Visco of the Ventilator...

Any ideas how I'd do this?

If u have AC, u have to check also if the auxiliar electrical ventilator runs ok at temp of 91ºC & 98ºC

No AC - fortunately as that'd confuse matters even more!

Only hot close to the thermostat housing, or along the whole length?

Hotter nearer the thermostat housing.

[klobuznik]

Turn on the engine....the ventilator will move...with cold engine you will be able to stop the ventilator with an rolled newspaper putting it into the blades, as it moves free...

As soon as the temperature reches the middle of the temp indicator, the ventilator will fix itself and will move quicker. It will sound like an aeroplane when you accelerate. Try then to stop it with the rolled newspaper and it will cut it in pieces !!!!!!!!!!!

If not, then you will need a new visco...it's about 150 Euros and 5 minutes to replace it.

here you can see the Visco.Number 2.




Hoy to change it:

[Gt6s]

Just re read your original post. In particular the bit about the thermostat. You have one fitted which is permanantly open for testing. I do not know what method you used to do this. But you need to be aware these are not a conventional stat which opens single port when hot. These cars use a changeover stat which opens one port and closes another. This changes water flow from round the block "closed" to through the rad when hot.
If you remove stat completely or stat is not allowed to change over you will have NO CIRCULATION WHATSOEVER ( I tried mine without stat, "how I know" ) engine will get almost instantly hot which I gather is what yours is doing.
Backflush the rad regardless as I previously suggested, the remark about the noisy water pump ties in. Quick job anyway.

[Martinaston]

You may be lucky and get away with just changing the gasket after it's overheated but be prepaired just in case the head has cracked as well

Sounds to me like it's the fan that was the original problem.
Hope it goes well

[Gt6s]

You may be lucky and get away with just changing the gasket after it's overheated but be prepaired just in case the head has cracked as well

Sounds to me like it's the fan that was the original problem.
Hope it goes well

He has allready done the head up and gasket he is now trying to get the thing to cool.

Prob right about the fan though, being part of the original problem.

Viscous fans BOY I HATE THOSE FN THINGS !

Why mine is now electric

[e30-320i]

Just re read your original post. In particular the bit about the thermostat. You have one fitted which is permanantly open for testing. I do not know what method you used to do this. But you need to be aware these are not a conventional stat which opens single port when hot. These cars use a changeover stat which opens one port and closes another. This changes water flow from round the block "closed" to through the rad when hot.
If you remove stat completely or stat is not allowed to change over you will have NO CIRCULATION WHATSOEVER ( I tried mine without stat, "how I know" ) engine will get almost instantly hot which I gather is what yours is doing.
Backflush the rad regardless as I previously suggested, the remark about the noisy water pump ties in. Quick job anyway.

my car didn't have a thermostat for 6 months when i bought it and the temp guage never got above 1/3 are pre f'/facelift different???

[alackofspeed]

Just re read your original post. In particular the bit about the thermostat. You have one fitted which is permanantly open for testing. I do not know what method you used to do this. But you need to be aware these are not a conventional stat which opens single port when hot. These cars use a changeover stat which opens one port and closes another. This changes water flow from round the block "closed" to through the rad when hot.
If you remove stat completely or stat is not allowed to change over you will have NO CIRCULATION WHATSOEVER ( I tried mine without stat, "how I know" ) engine will get almost instantly hot which I gather is what yours is doing.
Backflush the rad regardless as I previously suggested, the remark about the noisy water pump ties in. Quick job anyway.

I helped tyrehit remove and re-fit the head, and I was the one that removed the original thermostat. I didn't spend much time comparing the old and new thermostat, but I'm pretty sure the original one was the same as the new one I installed - closed variety, not bypass.

The car in question is a post face-lift car, perhaps this explains the difference between his and yours?

Anyhow, assuming the thermostat is the correct one........ the plot is still as thick as it was before!

[tyrehit]

Just re read your original post. In particular the bit about the thermostat. You have one fitted which is permanantly open for testing. I do not know what method you used to do this.

The old thermostat was damaged but enough was left to support the O-ring so the thermostat housing could be sealed.

But you need to be aware these are not a conventional stat which opens single port when hot. These cars use a changeover stat which opens one port and closes another. This changes water flow from round the block "closed" to through the rad when hot.If you remove stat completely or stat is not allowed to change over you will have NO CIRCULATION WHATSOEVER ( I tried mine without stat, "how I know" ) engine will get almost instantly hot which I gather is what yours is doing.

In the thermostat housing breakdown diagram that was posted above which port is closed when the thermostat opens?

Backflush the rad regardless as I previously suggested, the remark about the noisy water pump ties in. Quick job anyway.

Will do.

You may be lucky and get away with just changing the gasket after it's overheated but be prepaired just in case the head has cracked as well

I've had the head pressure tested and skimmed.

my car didn't have a thermostat for 6 months when i bought it and the temp guage never got above 1/3 are pre f'/facelift different???

Another friend is running his without a thermostat and tells me that he's had no problems.

[tyrehit]

Flushed and back-flushed the radiator last night. I was able to turn the tap to a high flow rate and it all flowed through and out of the radiator with no problems. The only slight thing I'm not sure about is what sort of flow rate I should get out of the bleed nipple next to the radiator inlet. It was reasonably strong but occasionally stuttered very slightly as if air was coming out as well. I checked for obstructions but only removed a very small amount of (I presume) crystallised coolant. A visual check of the radiator didn't suggest anything abnormal either.

I haven't tested the car since but I don't think the situation will have changed.

I've read (and seen) that there's a bleed plug on the side of the block below the exhaust manifold; is it worth unscrewing this?

Any other suggestions welcome!

[alackofspeed]

Just re read your original post. In particular the bit about the thermostat. You have one fitted which is permanantly open for testing. I do not know what method you used to do this. But you need to be aware these are not a conventional stat which opens single port when hot. These cars use a changeover stat which opens one port and closes another. This changes water flow from round the block "closed" to through the rad when hot.
If you remove stat completely or stat is not allowed to change over you will have NO CIRCULATION WHATSOEVER ( I tried mine without stat, "how I know" ) engine will get almost instantly hot which I gather is what yours is doing.
Backflush the rad regardless as I previously suggested, the remark about the noisy water pump ties in. Quick job anyway.

You were correct ! It was the thermostat that was at fault. The replacement bought from GSF was of the divert variety, but we deduced wasn't doing the job correctly. We looked at it closey, and concluded the divert spring wasn't very strong, so took it back, and got one from ECP which has a stronger spring........

RESULT - car is now running, and very smoothly!

Oh... and on the basis of what we now know, the reason the gasket popped was the original thermostat broke , and stopped diverting fluid to the rad..... An expensive repair for the sake of a £10 component.

[Brianmoooore]

I've read (and seen) that there's a bleed plug on the side of the block below the exhaust manifold; is it worth unscrewing this?

That's a plug for draining the block when you do a coolant change, not an air bleed.
Don't expect to have any skin left on your knuckles if you attempt to unscrew it!