Descaling a Sprint radiator

[GrahamFountain]

I'm sure that the cooling system is neither being presurized by a leak from the head nor losing pressure from the cap.

And these expansion tanks are much better then the plastic bottles used on the early TR7s. They went to these metal ones for the 79 year model, as I remember.

Graham

[sprint95m]

Any help towards the alternative to the Dolomite expansion tank?

Volvo 850 is what I used, but that was for a slant four.

The 1500TC has more under bonnet space so there are many more options. Mind you the Volvo ones are cheap .

My 1500tc has the expansion coming from the top of the radiator, would it be better from the thermostat housing?

No, using a take off from the thermostat housing is not necessary because the engine sits relatively low.


It may be worth starting a separate thread Mark, rather than have your questions in this one?



Ian.

[sprint95m]

Mark,
I have a used VW header tank c/w cap, the spherical one common to most VWs, Skodas, Seats etc.
It is quite bulky to post, but if it is any good to you, the cost including postage is £10.
Please PM if interested.


Thanks,

Ian.

[sprint95m]

I'm sure that the cooling system is neither being presurized by a leak from the head nor losing pressure from the cap.

Fair enough. Nothing more to say.




Ian.

[GrahamFountain]

I've finally got round to instrumenting the radiator with digital thermometers at top left and bottom right corners. What that seems to show is that the fan is coming on before the thermostat is fully open - it comes on when the top temp is around 80C and the bottom temp is only around 60C. But once on, the top temp goes up to 85C or so, and the bottom temp is consistently about 10C less. I can't actually measure the temps very well while driving yet - there's too much EMI between the ignition and the thermometers to get reliable readings, but it does look like there's no problem with overheating at all, and it's just that the fan's coming on too low. I do have some cable screening on order from China (still cost twice what the thermometers cost), but it mightn't be here till mid May.

The problem is that I can't easily get a switch that's got higher switch on and off temperatures. So I was wondering about, as a temporary fix, fitting a lower temperature thermostat, and seeing what happens. I think I have one that's starts to open at 82C and is full open at 88C. As a matter of interest, it's opening just below 1/2 on the dash gauge, and looks like it's fully open just above.

Any suggestions about what to get or where to get it?

[gmsclassics]

I've been using a Revotec electronic fan controller for years now. They are available below plus at other suppliers. Beauty is they can be set at any temperature you like and are available for various hose sizes. Not cheap but once fitted in the top hose and set they go for years - or mine has at least.

http://www.burtonpower.com/revotec-elec ... efc32.html

Mine is set to come on 5-7 degrees C above the thermostat setting. If you get the setup correct the fan should never come on whilst driving, only when car is stationary or crawling in heavy trafic on a hot day. Beauty of this is you can keep adjusting the setting until it is just right for your car.

I also use a 170F/77C thermostat to give me a bit more leeway, a temperature gauge that tells me the real temperature and another tip is to wire the fan to be powered still after the ignition is switched off until the temperature gets down and the fan controller switches it off automatically. That helps prevent localised boiling on really hot days when the car is stopped.

By the way, i had my radiator re-cored about 15 years ago and it is still fine. All i do is use good antifreeze and change it every three years.

Geoff

[GrahamFountain]

I think I've fixed all the problems with why the fan stayed on too long, mostly down to the switch being in the top not bottome hose and the system being scaled up. So I moved the sensor and when that didn't fix it fully, (though I didn't want to do it this way) I descalled with a washing-up tab - actually 2. I put one in and ran for an hour and flushed, which made things a bit better but not enough. So I used another and drove round for a couple - three hours, cycling the temperature a couple of times. That made a big difference. I also fitted a 75 degree thermostat instead of the 82 degree one; though I think I'll switch back for the winter.

I'd checked the voltage stabilizer, which was wrong, at about 11 volts, but seemed stable. And as that does not affect when the fan switched on or off, I had left it alone, so I could see the effects of all the other changes all in the same context. But at some point in the process, the temperature and fuel readings started to get erratic: after reseating the top fuse once, I gained nearly half a tank and the temperature went to full scale before the fan kicked in - luckily I still have the rad instrumented, so I knew I wasn't really overheating. But clearly the sabalizer had gone. I used the kino-restorative technique and got it back to working poorly, but consistantly - the reading was around 2/3rds to 3/4 full hot with the fan on - but thought now was the time to fix it.

I wondered, it being mechanical, if I might be able to fix it. But not actually knowing how it worked, I got a new one first. That appears to be a solid state one - I can see the base is actually a small circuit board. I suspect its an L7810 in a TO-220 plastic can.

I managed to get the cover off the old one without buggering it too much and what I found inside is shown in the attached photo. The interesting thing is that there's clearly an adjustment. So, if you have one that just mis-reads, but is otherwise okay, it may be possible to re-calibrate it to 10v or so, rather than buying a replacement. Well it might work.

I think, looking at how it works, part of the problems I had was a poor earth, which connects at the sliver tab (front right) to the can, then through the mounting screws to the bulkhead. As it's the current through the wire from the output to earth that heats the bi-metal strip, and reduces contact pressure on the points, if that earth is poor, the strip won't heat up enough at the right voltage, and the output will be high. If it loses all earth, it obviously has to output battery voltage - unless the points are corroded and there's nothing to earth anyway.

I did try putting it back, after cleaning all the earth contacts, but I had played with it a bit - to see how the contact resistance changed as I bent the strip (not very well) - and it didn't work properly any more – while the gauges were stable, the measured voltage was all over the place. I suspect it was oscillating at a frequency that aliased with the sample rate of the DVM - it jumped about as if possessed; I think that it was p155 (to paraphrase Mike Absalom's Saga of the Ancient Britton).

So I put the new one in, and that's brought the reading down to just below to just over half driving round town in the 30 zone. I want to take it down the M55 for a bit and check its all okay now.

Still, I though the picture of the internals of the old Smith's stabilizer, and that there is a possible adjustment might be worth a note.

Graham

[GrahamFountain]

Found at least one situation in which the fan does and should come on while driving at 30 mph - a 30 mph tail wind.

Graham