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521 Over heating problems

Matt H

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Proper timing, all the combustion takes place in the combustion chamber with piston close to TDC. Late timing (retarded) exposes more cylinder wall and exhaust port to higher temperatures and this heat is absorbed by the cooling system. tremendous loss of power too.

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  • 2 weeks later...

Hey sorry for the delayed reply. I had been travelling these last couple of weeks...

Thanks everyone for chiming in. So I just pulled the radiator and flushed it and it it appears to be running again now! There was no obvious blockage - although a fair amount of dirty water came out from the very bottom of the radiator. I flushed through a few times until it ran clear. Bizarrely there also sounded to be something metal rattling around inside the radiator.

It was idling a little hot on the driveway still (maybe 2/3rds) but after I took it around the block a few times it mellowed out. I'm a little surprised its running smoothly now to be honest as it was overheating pretty quickly before pulling the radiator. Is it likely that there was just trapped air in the system as a result of the radiator running low?

Also shot the thermostat housing and its reading at 176 after it had been running for a while.

Thanks all 🙌

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The rattling is just solder droplets.


Should read about 10 degrees higher at 185F.


The highest point in the cooling system is the thermostat housing and the engine is tilted up at the front. Any air will work it's way there even without a push from the water pump. The L series thermostat is mounted horizontally so as soon as it opens, air escapes to the top tank of the radiator. Just check the radiator level after warm up after re-filling it and top up. Always use distilled water.


Get a coolant recovery radiator cap and run the overflow hose into a container that is 1/2 full with the hose submerged. On hot days or often during the heat soak after engine shut off the cooling system can over pressurize and expel coolant. This system catches it and when the engine cools, the air it the top tank contracts and sucks the coolant right back in. This keeps the radiator topped up automatically. I used to top up every week (this dilutes the anti freeze) and ended up running the rad about an inch low to allow for expansion. With the recovery system I now top up a cup once a year.



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ok thanks @datzenmike  I'll look into installing an overflow system. Is a coolant recovery radiator cap essentially just a closed cap with no pressure release? Do they have different psi ratings?

I'm not sure what it is with my car but it has this great habit of when I fix something - something else immediately goes wrong hahaha.

I might put this under a new thread but since fixing the overheating issue i'm not noticing the car is having a harder time starting. It tends to struggle to start now and when I try to rev the engine or use the choke it dies. It takes me quite a few attempts to get it running. After it's running its typically fine however I am noticing occasionally it can stutter when pulling away in first gear almost like its miss-firing or something. Do you think perhaps where coolant leaked all over the alternator it might of messed it up or could it be the starter and or spark plus are on the way out


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14 hours ago, Matt H said:

I'm not sure what it is with my car but it has this great habit of when I fix something - something else immediately goes wrong hahaha.

That's just old cars in general. You don't notice the other problems while you're focusing on the others.

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