Cooling System

[alanrichey]

My cooling system has raised it's ugly head again.   I was driving along quite happily when the temperature suddenly jumped to 110°C and stayed there.  Oddly my fan (the 95°C, thermostatic switch is in the top hose) did not come on until about 10 minutes later.   My first thought was a jammed thermostat, but having removed it the symptoms were still the same, a quicker than normal warmup finishing up well above 100°C.   Next I checked the coolant level and that was normal, although a small amount had come out of the pressure cap and into the overflow bottle.

The fact the 95°C fan does not trigger until 10 minutes after the engine had got to over 100°C seems to show the water around the switch is getting hotter by just normal conduction rather than circulation.  I think I confirmed that by removing one of the hoses and putting the end in a bucket and even after the engine warmed up there was no water coming out. 

So our (I was working with AndyW) thought that it must be either a failed water sump or a blockage.   There was no noise coming from the pump and the auxiliary belt was working perfectly so if it is the pump it must be the drive shaft that has failed.   I  am going to do a reverse flush of the system when it gets a bit warmer outside (there is no rush to fix it) to check for a blockage, but wondered if:

a.    Have I missed something, could there be another reason ?

b.    Is there a definitive test I can do to prove there is no circulation ?

c.    Rather than try and replace the pump (notoriously difficult on the Rover T16 as it is built-in with the Power Steering pump) could I just fit an electric pump in the bottom hose ?    Has anyone fitted one to their kit ?   Did you have to remove the original water pump  (I guess if it is jammed it would cause a blockage, although a reverse flush should show if it has jammed) ?

Grateful for any thoughts on the way forward.

Al

 

Edited December 24, 2020 by alanrichey

[IanS]

Every water pump I have seen is an impeller type that provides little obstruction to flow when not turning so an electric pump in the bottom hose should work.

The heater circuit might be a problem and need its own pump.

[alanrichey]

Thanks for that.  No heater fitted so that isn't a problem.

[Peter Bell]

Could you have an airlock in the top hose where the thermostatic switch is? Would explain why the fan didn’t switch in.

[alanrichey]

Always a possibility in the weird Superspec cooling system design, but I did everything to get rid of any air.   And this was a sudden occurrence after 2 years of working perfectly, so I think it's safe to say something has broken.

[Sparepart]

Just a thought while the pre lunch fizzzz is in the grey matters .... why not take the fan switch and put it in with your boiled egg tomorrow and check that it switches on before the egg is ready?

[blue]

I think it’s safe to say that the water pump is not doing what it’s supposed to do 

the reason the switch does not come one till around 10mins after is due to thermo siphon effect.  
a Davis Craig type pump will do the job but fit it with its controller 

i have one fitted to my zero from when I built it ~ I removed the impeller from the pump and never had a problem 

[geordie40]

I had the water pump changed when the Head gasket blew on my Superspec and the chap said it's not to difficult in our cars as you can get to it easier than when fitted to the Rover, it's only 5 or 6 bolts and the pump itself isn't expensive.

Your sudden temp rise sounds exactly like my HG failure except mine eventually started blowing white smoke but not for sometime after the HG went

[alanrichey]

Trouble is I can’t guarantee the water pump has failed.  As you know, on our cars the belt pulley drives the power steering pump which then drives the water pump.  So the problem could be anywhere in the train.  When it warms up a bit I will be investigating.

I’m hopeful it isn’t the head gasket, as there is no loss of coolant and the oil is still clear.

[geordie40]

Fingers crossed it's not the HG but my oil was clear and no real coolant loss for about 20-30 miles.

The chap who did all mine said the water pumps are usually ok but seeing as he had whole thing apart it got changed. However he did point out that despite the milage being low it was still a 24 year old engine so anything is possible

[Grim]

Alan,

How do you know the temperature reading is correct? If the fan does not come on until some time later, and that is controlled by a separate switch, doesn't that tie in with the temperature gauge over reading?

[alanrichey]

The Superspec has 2 independent temperature sensors, one for the gauge and one for the ECU.  The ECU feed gives me an exact temperature reading, and over the last few years I have been able to use that to calibrate the gauge.  Before this event I could see that the fan switched on at 95C, which equates to the ‘O’ of the word NORMAL on the gauge.  So these 3 independent sources give me a very good handle on how the cooling system I’d doing.

[alanrichey]

Just to close off this thread, the problem has gone away, but I have little or no idea what caused it in the first place.   I checked all the component parts and everything was working as advertised, but still no apparent circulation.   So I took some hoses off and reverse flushed the whole system.  But nothing came out that might have caused a blockage, every part of the system was clear.   I then refilled the system, but using a slightly different method than before, by removing the pipe that goes from the original heater feed to the top centre of the radiator (A Superspec feature , and the highest point in the system) while the engine was running, topping it up as required until all the air had bubbled out.  

Reconnected the pipe then ran the engine, the temperature climbed up to the early 80s, at which point I felt the top pipe warm up (I have an 82C thermostat) then at exactly 95C the fan kicked in and the engine cooled off to 91C when the fan turned off, then the cycle began all over again.   A decent run out (Legal, as I was picking up my medication, although I would be hard pressed to explain why I covered 24 miles when the pharmacy is only 1.5 mls away ) showed she actually stabilised nicely at 84C and the fan wasn't needed.

So I am a bit frustrated.   The only think I can think of that makes any sort of sense is that I had an air lock that had migrated to surround the water pump with air, thereby stopping any circulation.  It is an unfortunate design problem with the Rover engine that those engines destined to have an air conditioning pump fitted have a redesigned water pump attachment that means it sits at the top of an inverted 'U' so an air lock could form around the pump.

I'm quite pleased to have discovered a much better way of filling the cooling system that just about guarantees no air locks.  You would think after nearly 8 years with the car I would have figured that out earlier.

[fry61]

There will still be air to be liberated from the water -- is it possible to install a bleed nipple close to the pump?  Florin has 2 ordinary central heating bleeds on 15 mm tees in the feed & return pipes for the heater, which is the highest point on her CVH system.

[alanrichey]

I can't do one close to the pump, it is mainly within the engine block.   But it makes sense to put one at the point where I disconnect the hose at the top of the radiator.   Would be easier to bleed the system regularly,