Radiator blockage?

[Dryad]

My Minor, after being my daily driver for a few years, has spent some years stood outside under cover, with the engine been run every few months to stop it siezing up, and now I am going to get it back on the road. The engine runs sweetly but I have noticed that it's overheating after idling for fifteen minutes or so. However, whilst the top of the radiator is scaldingly hot the bottom is cool. Obviously, it's a probably a blockage somewhere, but is it likely to be in the radiator or in the engine block itself? Either way, which is the best method for unblocking it?

[svenedin]

It's probably the radiator that's blocked and even if the blockage is elsewhere after standing for some years you may as well flush the radiator. The radiator is only held in by 4x bolts, 2 on either side. Disconnect the top and bottom hoses, remove the 4 bolts and lift the radiator straight up and out. Then tip all of the rusty water out and flush vigorously with a garden hose. Fill the radiator with water, shake it, tip the water out and repeat until the water is clear. Check that when the radiator is full of water that water runs freely from the bottom outlet.

Reinstall, fill with water, start the engine and see what happens. If all is good make sure you use antifreeze as winter is coming and antifreeze also contains corrosion inhibitors which loose effectiveness over time.

Make sure the fan belt is turning the water pump pulley as if not the water pump cannot circulate the water. Water pumps sometimes seize with prolonged lack of use.

Stephen

[Dryad]

Thanks Stephen, I'll do that at the weekend.

[myoldjalopy]

It is possibly unlikely that your radiator drain tap - and maybe the engine block drain tap - is working, so be prepared for rusty water to gush out from the bottom hose when you undo it........

[svenedin]

It is possibly unlikely that your radiator drain tap - and maybe the engine block drain tap - is working, so be prepared for rusty water to gush out from the bottom hose when you undo it........

Yes. The radiator drain tap is prone to seizing and with a vehicle that has been standing for a few years I thought it best not to mention it at all. The flow from the drain tap is slow even fully open. It is very useful with a pipe attached to the drain when draining the coolant with the intention of reusing it but if the radiator is full of rusty crud it is likely to block the drain pretty much instantly anyway.

Stephen

[oliver90owner]

MOST likely it is the thermostat that is faulty. It is unlikely that the radiator has mysteriously blocked itself while sitting doing nothing.

The radiator will be filled with an antifreeze mixture which will help to avoid internal engine corrosion.

First determine the actual temperature. Scalding temperatures are achieved long before the thermostat is even likely to open. That means there may be no fault at all!

[svenedin]

MOST likely it is the thermostat that is faulty. It is unlikely that the radiator has mysteriously blocked itself while sitting doing nothing.

The radiator will be filled with an antifreeze mixture which will help to avoid internal engine corrosion.

First determine the actual temperature. Scalding temperatures are achieved long before the thermostat is even likely to open. That means there may be no fault at all!

I don't understand that logic. The OP says the top of the radiator becomes extremely hot but the bottom remains cold. If the thermostat is stuck closed how does the top of the radiator get scalding hot? Antifreeze does contain corrosion inhibitors but those inhibitors are used up over time so if the car has been standing for several years there is unlikely to be any corrosion inhibition at all (the antifreeze effect persists).

I don't think the radiator did block itself sitting doing nothing. It would have blocked when the thermostat opened and all the rubbish in the block coolant tried to go through the radiator.

Stephen

[myoldjalopy]

No guarantee that there is any antifreeze in the car. We hope the days of running Minors as 'old bangers' is over, but one never knows.
No doubt any problem will be resolved with the OP's car and antifreeze will then be added...

[Dryad]

Thanks all. I did put antifreeze after I last time had to remove the radiator (removing the engine) but that was about seven years ago. However, I will inspect the thermostat and will probably replace it anyway, just to be on the safe side. Plenty to keep me busy at the weekend!

[svenedin]

Please let us know how you get on.

Stephen

[Dryad]

Please let us know how you get on.

Will do.

[svenedin]

Personally, I would flush the radiator first as it will need doing regardless and it is an easy win. Then test. Removing the thermostat housing can be an absolutely terrible job if the housing has fused itself to the studs with corrosion. Only change the thermostat if you really have to.

Stephen

[myoldjalopy]

Yes, the thermostat may be OK so try the flushing first. However, if you do decide to remove the thermostat, give the nuts on the housing a good dousing in plus-gas for a day or two beforehand. I had to replace my housing due to it developing a small hole and, with the plus-gas, had no problems. If you can then get the nuts off, it may be worth dribbling plus-gas over the studs for a while as well so it can seep down the threads. Careful use of a rubber mallet may also help loosen things. These housings are known to be stubborn to remove.
I put copper grease on the studs when fitting the new housing.

[svenedin]

Absolutely. I put silicone grease on the studs and I bought a stainless steel stud, nut and washer kit from Minispares so determined was I never to repeat the absolute destruction that was required last time! My theory for using silicone grease is that it is an electrical isolator as well as being a lubricant. The corrosion here is electrolytic because the metals are dissimilar so a grease that actually conducts electricity like copper grease seems counterintuitive to me. Of course I may be totally wrong on this.

Stephen

[michael4]

In the boating world we have been known to use something called Duralac. It is a rather nastily coloured jointing paste that is used between dissimilar metals. For example I would use it with stainless fittings on an aluminium mast.

I would think it would do well on a thermostat housing and studs

[oliver90owner]

Let’s actually think about this , before posting (basically) rubbish.

Stored outside for several years with water only would have damaged something by now!

Water is less dense as the temperature rises, so hot water WILL be at the top of the radiator.

Water over 60 degrees Celsius is enough to scald. Thermostats don’t open until 78 or 88 Celsius?

Anti freeze does NOT lose antifreeze properties with age - it can slowly lose corrosion resistance.

I think someone needs to use a modicum of logic. I’ve left engines for years and have never blocked a radiator just by starting the engine. If the radiator is blocked, it was mostly blocked BEFORE the car was laid up. Unlikely to overheat ticking over if it didn’t overheat while working hard, previously. Corrosion is as a sediment, not large lumps that are conveniently pumped round to the radiator.

All in all, just someone trying to justify their dim diagnosis - dim because that was the ONLY possibility given.

YES, it could be a blocked radiator but UNLIKELY!

[myoldjalopy]

"Anti freeze does NOT lose antifreeze properties with age - it can slowly lose corrosion resistance."
Nobody said anything different. In fact, Stephen twice in this thread pointed out that anti-freeze loses corrosion resistance with age. He also made it clear that the antifreeze effect does not diminish over time.

[svenedin]

I really don't understand the argument or why it has to be so heated (scalding maybe ).

Unless I fundamentally misunderstand how coolant circulates from the block to the water pump and through the radiator I cannot fathom how a failed thermostat gives the symptoms the OP has. When the thermostat is shut water circulates around the block and through the bypass hose which acts as a shunt. The water cannot get to the radiator when the thermostat is shut. As the water circulating round the block gets hot, the thermostat starts to open and water flows into the radiator via the top hose. The temperature at which the thermostat opens is determined by the particular thermostat fitted. Typically 82c but may differ. A thermostat can fail shut, wide open or may stick partially open. So yes I agree that a problem with a thermostat not opening properly can cause the engine to overheat. BUT, the OP says the engine warms up, the top of the radiator gets scalding hot but the bottom radiator hose stays cold. So there is definitely a problem with circulation of water through the radiator. Of course there could be different explanations for this. A blocked radiator, a thermostat that isn't opening properly, a blockage elsewhere, a slipped fan belt not driving the water pump properly even a seized water pump. All I was suggesting is that flushing a radiator is very simple and is almost always a worthwhile thing to do with a car that has been left standing for years. Surely, it is worth doing first and then see if that did the trick?

Stephen