Series 3 Overheat after motorway run

Hi all,

Touched on this before but would love some further advice

I’ve got a 1982 S3 SWB, running a Weber carb. On a run the temp is fine, but when I slow down (eg motorway exit to traffic) it gets hot - about 3/4 on the gauge). It doesn’t really come down until I get some decent speed (30MPH) again. It also tends to overheat if doing heavy uphill off-road work in low range.

It’s running the original fan with shroud and cowling.

The radiator has had a flush and there is a new thermostat - this cured more series overheating. I’m happy the thermostat is decent, and the radiator *appears* in good shape.

Is this normal? It seems a bit surprising given how overbuilt everyone says the cooling system is. Ideally I’d love to keep the original set-up. Could it be a water pump issue? Or is it more likely to be a new radiator job, or simply that it might be a wise idea to get an electric fan?

If going the eclectic fan route, would a slimline one fit inside the existing cowling between the rad and the mechanical fan? Concerned you would see it from the front if I mounted an additional pusher fan, and since I don’t want to shell out £££ on a revotec kit I’d prefer to keep the original one as the ‘standard’ fan just in case the electric one fails.

Electric fan will not help this issue.
First check is the tension/condition of the belt. If worn thin they can slip even if tight as the belt bottoms out in the pully's
How old is the radiator? Could have internal clogging.
There was an issue with a batch of replacement pumps some time ago where the impeller was coming loose on the shaft, although this issue tends to show up pretty quick when driving.

tottot said:

Electric fan will not help this issue.
First check is the tension/condition of the belt. If worn thin they can slip even if tight as the belt bottoms out in the pully's
How old is the radiator? Could have internal clogging.
There was an issue with a batch of replacement pumps some time ago where the impeller was coming loose on the shaft, although this issue tends to show up pretty quick when driving.

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My reasoning with the electric fan is that it would spin faster at idle than the standard one? On my 110 which has a kenlowe it runs cooler at slow/idle than at speed!

Can’t say I know about the radiator - I’ll admit hoping I don’t have to bite that bullet. The belt seems in good condition.

At idle the engine does not produce the heat it does when working so slower turning fan is not a problem.
That is also the reason your electric 110 one cools so much. I run an electric myself and have the fan controller set to cut the fan off when temp drops below 88 degrees.
I have an after market gauge that is accurate and reads in numbers

tom.brandford said:

My reasoning with the electric fan is that it would spin faster at idle than the standard one? On my 110 which has a kenlowe it runs cooler at slow/idle than at speed!

Can’t say I know about the radiator - I’ll admit hoping I don’t have to bite that bullet. The belt seems in good condition.

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An electric fan won't spin at all unless the engine overheats. Unless you have a manual override switch.

I think the thermostat on your 110 isn't working, or you have a problem with the temperature sender.

Is the fan on the S3 fixed, or a viscous fan?

Turboman said:

An electric fan won't spin at all unless the engine overheats. Unless you have a manual override switch.

I think the thermostat on your 110 isn't working, or you have a problem with the temperature sender.

Is the fan on the S3 fixed, or a viscous fan?

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110 fan is a manual fan switch (meant with fan on, it runs cooler at low speeds than motorway despite the motorway speed airflow)

S3 fan is fixed

tom.brandford said:

My reasoning with the electric fan is that it would spin faster at idle than the standard one? On my 110 which has a kenlowe it runs cooler at slow/idle than at speed!

Can’t say I know about the radiator - I’ll admit hoping I don’t have to bite that bullet. The belt seems in good condition.

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Almost all 40 year old radiators will have some internal silting up.
I would try removing the hoses, and back flushing the radiator using a garden hose until the water runs clear.
The refill with the right antifreeze mixture, and see how you go.

Another good diagnostic technique is to remove the thermostat completely, and drive around. the engine should barely heat up at all. If it does, you have a problem with the rad, or blockage, or air elsewhere in the cooling system.

tom.brandford said:

110 fan is a manual fan switch (meant with fan on, it runs cooler at low speeds than motorway despite the motorway speed airflow)

S3 fan is fixed

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Remember an engine produces more heat when it is working hard, such as at speed on a motorway, so there is more heat to be lost by the cooling system.

try turning the fixed fan blades by hand with the ignition off. If it turns easily, the belt is slipping.

I put one in front of rad, might be worth checking the sender unit with it connected to gauge and in a pan of water with thermometer while heating it up

Mine was running on the cool side even in 30+ temps in the Canaries, took the stat out and found it was wedged wide open, yours might be doing the opposite, first port of call, check stat. Easy fix. Then rad, esp if it’s an old one

Turboman said:

Remember an engine produces more heat when it is working hard, such as at speed on a motorway, so there is more heat to be lost by the cooling system.

try turning the fixed fan blades by hand with the ignition off. If it turns easily, the belt is slipping.

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Belt does seem to be turning at good speed with ignition on (I have the shroud so a bit of a pain but will check properly)

steve2286w said:

I put one in front of rad, might be worth checking the sender unit with it connected to gauge and in a pan of water with thermometer while heating it upView attachment 291681

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Gauge seems to be accurate - we checked with IR thermometer when it was running hot before. I do wonder if this is the way forwards - it would really be the occasional heavy duty low range use or when I occasionally have to drive it into London (M11 race track to north circular standstill)

Fatrover said:

Mine was running on the cool side even in 30+ temps in the Canaries, took the stat out and found it was wedged wide open, yours might be doing the opposite, first port of call, check stat. Easy fix. Then rad, esp if it’s an old one

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I have a new stat in there and at speed keeps steady temp - I do wonder about the rad efficiency. Given it’s not doing anything hard for the rest of summer this might be a ‘kick it into the long grass’ moment - only really noticing at the moment as using it for a house move from London to Norfolk

It sounds to me like you have done everything else already.

If it wur mine I’d do the following (cheap first)

Test the bleed under the manifold.
Test the thermostat in a pan.
Couple of dishwasher tabs and a flush.
Little cry in a dark room.
Try and wobble the fan to judge play in the pump.
Check the matrix is clear of cyclists and wheelchair parts.
Try ignoring it for as long as possible.
Replicate the reasons but use a (borrow a) infra red laser thing to test true temp of the engine.
Repeatedly bang the gauge in frustration.
Have another cry.
By now, repair the other fifteen things that have broken or worn out around the car.
Repeat all of the above.

Eventually I’d probably stop going on motorways.

Bobsticle said:

If it wur mine I’d do the following (cheap first)

Test the bleed under the manifold.
Test the thermostat in a pan.
Couple of dishwasher tabs and a flush.
Little cry in a dark room.
Try and wobble the fan to judge play in the pump.
Check the matrix is clear of cyclists and wheelchair parts.
Try ignoring it for as long as possible.
Replicate the reasons but use a (borrow a) infra red laser thing to test true temp of the engine.
Repeatedly bang the gauge in frustration.
Have another cry.
By now, repair the other fifteen things that have broken or worn out around the car.
Repeat all of the above.

Click to expand...

I fully approve of this logic and is pretty much what I’ve done - I have a new thermostat as well as a new one already in there, and rad has been flushed. Temp gauge is accurate, and on non motorway runs temp stays still.

I’m thinking (maybe?) it’s normal - I do tend to run it at 60 on the motorway. Only issue is steep low range work in hot weather - maybe will get an electric fan at some point to compliment rather than replace (eg a cheap pusher). It won’t be doing motorway runs for much longer at least!

tom.brandford said:

I fully approve of this logic and is pretty much what I’ve done - I have a new thermostat as well as a new one already in there, and rad has been flushed. Temp gauge is accurate, and on non motorway runs temp stays still.

I’m thinking (maybe?) it’s normal - I do tend to run it at 60 on the motorway. Only issue is steep low range work in hot weather - maybe will get an electric fan at some point to compliment rather than replace (eg a cheap pusher). It won’t be doing motorway runs for much longer at least!

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Did you check the fan as per post number 14?

lynall said:

Did you check the fan as per post number 14?

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Yes checked it earlier and won’t turn when off so not slipping

Don’t mount the fan on the ribs. It will vibrate and burst about ten of them. Trust me, I know