Classic cars forum & vehicle restoration.

Oldtimer · Joined: 13 Jul 2016 Posts: 5 Location: Southampton

Hi, I new to this site so if this is in the wrong place please forgive me!

I have a 1931 Citroen, which i have owned for many years, it has a side valve engine with water pump unpressurised cooling system. In traffic, no matter how heavy the traffic, the car is fine. Driven at a steady speed say about 35mph (top speed about 50mph) again the car will go on all day long. However, when driven hard the engine overheats and forces water out through the radiator overflow Embarassed

whether because it is overheating or somehow the system is getting pressurised.

Any opinions gratefully received.

peter scott · Joined: 18 Dec 2007 Posts: 7120 Location: Edinburgh

Welcome to the forum Oldtimer.

You might have a blown head gasket. Can you see any sign of oil or bubbles in the header tank?

Peter
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Oldtimer · Joined: 13 Jul 2016 Posts: 5 Location: Southampton

Hi Peter,

Thanks for your reply, no that is the strange thing there is no sign of oil or bubbles in the header tank. I must admit my thoughts are that it is a blown head gasket but none of the usual signs are there, other than water being pouring out when driven hard.

I guess I'll have to bit the bullet and take the head off, trouble is head gaskets are getting hard to find, hence not cheap!

Bitumen Boy · Posted: Mon Jul 18, 2016 7:24 pm Post subject:

Oldtimer · Joined: 13 Jul 2016 Posts: 5 Location: Southampton

[quote="Bitumen Boy"]

Kenham · Joined: 12 Mar 2012 Posts: 209 Location: Kent

I think I would be looking to see if the radiator is blocked first before taking the head off. Flow test the rad and make sure the fins are clean and air can pass through. Also flush the block, its amazing how much crud you can get out of a block.

Phil - Nottingham · Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham

It seems more like;y to be a blocked core or silted up block. Clean before pulling engine apart!
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roverdriver · Posted: Tue Jul 19, 2016 9:44 am Post subject:

Are you sure that it is overheating? Non-pressure systems will lose water as the water heats and expands, and will do so until it finds its own level. When the engine cools, it looks as though the water level is too low, so unaware owners will top the water off. Then it expands and throws out water once again.

I am not familiar with Citroens, but suggest that perhaps there is somewhere in the system that is allowing a build-up of some pressure as the engine heats. Is there a by-pass at the pump that could be blocked? Is there a thermostat fitted that might be misbehaving?

Will look forward to hearing of progress.
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jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

Retarded ignition timing can also do this - check your timing is correct, and you have an appropriate type of petrol for your compression ratio.

jp

Salopian · Joined: 05 Jan 2010 Posts: 354 Location: Newport Shropshire

Had this with the 1928 Sunbeam 20.9 hp I used to run - also unpressurised but pumped system. Entirely due to lack of flow through the rad core - in my case due to a previous owner using ordinary rather than water pump grease in the pump. This had partially blocked the rad but a thorough flushing firstly with solvents and then descaler gave a complete cure.
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Oldtimer · Joined: 13 Jul 2016 Posts: 5 Location: Southampton

Update!
Firstly, thank you for taking the time to give me your advice.
1) Exhaust sniffer, having thought more about this I'm not sure it would work on an unpressurised system as the gases, I believe, would probably dispersed almost straight away.
2) Radiator blocked, I have just flushed the cooling system with "Thermocure Cooling System Rust Remover". It has certainly brought out no end of crud, however, it has also caused a number of water leaks so until these are sorted my overheating problem may or may not have been cured!
3) Loosing water, I fitted a gallon container to the radiator overflow pipe and managed to practically fill it, so I don't think it is just finding its own level.
3) Thermostat, this operates louvres in front of the radiator rather than restricting the flow of water through the radiator. Obviously it is easy to see if the louvres are operating correctly as opposed to the flow of water so that can be discounted.

The problem may have been cured but until I have cured the water leaks I won't know. Unfortunately due to other commitments this may be some time away. But thank you all for your suggestions, I will keep you informed of my progress in due course.

47Jag · Posted: Fri Jul 22, 2016 11:28 pm Post subject:

It's a long time since I used one (mid 60s) but as I recall it doesn't take much exhaust gas to trigger the sensor. I don't know what the modern units use but the one I used was a tube with yellow liquid inside. The air sample was sucked into the tube and passed through the liquid which would change the colour if exhaust gasses were present. So don't disregard this test if it's available.

Art

roverdriver · Posted: Sat Jul 23, 2016 9:31 am Post subject:

I'd strongly recommend finding a local reliable radiator shop, get them to clean out the whole radiator interior, then fix the leaks. It might cost a bit, but it will give you peace of mind.

While the radiator is off, then flush the block as much as you can.
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