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My Block is blocked - How to unblock?
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PostPosted: Sat Mar 17, 2007 3:53 pm    Post subject: My Block is blocked - How to unblock? Reply with quote

I've just put a new Thermostat on my 1975 J26 Mitsubishi Jeep.

Originally the engine was getting hot very quickly (but the heater was cold).
The first thing I did was to get the copper radiator cleaned out and a larger core fitted.
When I put the rad back in I found that some previous owner had removed the thermostat - (Hmmm).

I've had the water pump checked and its pumping water.
The rubber hosees are all tight and sealed.

The hose from the top of the termostat to the top of the radiator gets hot enough but the rad remains cold.

The thermostat works OK (I've checked it in a kettle).

Does this sound like the Block is blocked?

If so whats the best way to unblock it?

I've been told that Costic Soda used to be used for this purpose but if this is sensible to try what do I need to watch out for, what concentration to I need,how do I use it and is there anything I need to remove (e.g. Thermostat or electrics as I gather costic soda and electricity don't go together very well).

Any suggestions would be very much appreciated.
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PostPosted: Sun Mar 18, 2007 10:30 am    Post subject: Reply with quote

Hi Bernard

As a Stag owner (with all the cooling challenges!) I flush my cooling system out regularly with Holts Radiator Flush, you can get it from Halfords,it’s OK for alloy heads and has built in corrosion inhibiter, you have too leave it in for a couple of days, but it does a good job. There is a “quick flush” product but your problem sounds like it could be a bit stubborn so the stuff you leave in would be better.

They are not expensive both products are about a fiver. Costic Soda will work, but it also dissolve’s aluminium & steel (slowly) I don't know how you would get the strength and timming correct, an experienced mechanic may know, but without that input I would stick to proprietary stuff.

Cheers Dave
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PostPosted: Sun Mar 18, 2007 11:03 am    Post subject: Reply with quote


Of course - just because I've a "new" radiator that doesn't stop me using the flushing agent for the rest of the cooling system Embarassed

I've also been told by an industrial chemist that:
Caustic Soda - Hardens rubber hose and eats alloy.
Spirit of salts - Again eats alloy
Household detergent - might help release blocakages.

So the Rad Flush would be the best option, I'll give it and go and let it stay in the cooling system for a couple od days and let you knwo the results.

Many thanks for the tip. Bernard
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PostPosted: Sun Mar 18, 2007 11:55 am    Post subject: Reply with quote

Hi Bernard,

Just to add a little more to Daves good advice - have you checked that you don't have an air lock somewhere in the system?

The "cold heater" is a sign in many vehicles that an air lock has developed, which in turn restricts and can often stops the flow of coolant around the system. My Chevy for instance has a neat little screw valve added into the heater hose at the very top of the circuit and I'm always amazed how much air gets pruged out of it after I top up the system and release the valve - maybe worth trying first as its a no-cost option?

Hope this helps and not confuses the issue. Wink
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old gto

PostPosted: Sun Mar 18, 2007 2:29 pm    Post subject: Reply with quote

I`ve had problems with over-heating in the past that turned out to be a hose collapsing. Somehow the heat would cause the top hose to collapse, causing the coolant to stop flowing through the engine. Changing out the radiator hose for one with an internal spring is what solved it.
Have you considered this possibility?
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PostPosted: Sun Mar 18, 2007 8:15 pm    Post subject: Reply with quote

Scotty & Old GTO
Thank you both for these suggestions.

I'll investigate both.
My logic is based on the question "why someone should of removed the thermostat"?

Maybe because the waterways became blocked with crud\rust and so they used the thin radiator core to ballance the temperature out?

However, I will check for air locks and hoses collapsing (the hoses are both fairly chunky items and seem to keep their shape). other pipes are made of steel - hence my focus on build-up of rust.

I've popped some rad flush in and run the engine twice from cold - the second time it took longer to get to the "turn the engine off" mark, so progress is being made.

Once again thanks for the tips folk. What a generous bunch of people.

If anyone needs any help with the Microsoft range of office applications feel free to drop me an e-mail.
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PostPosted: Fri May 04, 2007 1:26 pm    Post subject: engine overheating Reply with quote

Reverse flushing the radiater may be helpful if the core of the radiater is blocked.basically putting a water hose at the bottom outlet of the radiater until the water turns clear when it flows out the filler cap would need to disconnect the bottom radiator hose the garages have a specail fitting they can hook up the air compressor as well would only need low pressure.Maybe doing the reverse flush and then the radiater cleaner remember to reconnect the bottom hose worth a try.rustyreks
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PostPosted: Fri May 04, 2007 7:51 pm    Post subject: Reply with quote


Than you for the tip.

It turns out there is a crack in the cylinder head so it's at an engineering firm waitting for them to weld and pressure test it.
At least it gives me an excuse for getting the timming sorted properly Wink

I was tempted to use Steel Seal but thought that I might as well go the whole hog so that when the Jeeps back on the road it should stay there for the summer (fingers crossed).

Mitsubishi UK have had their J27 rebuilt for the horse show at Badminton which they are sponsering this weekend and they have asked to include pictures of my J26 as part of the display. Pity I could provide the little beast itself!

Kind regards, Bernard
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