How hot should a top hose feel? Tried a Scientific approach!

Is it steaming, spitting, and generally misbehaving?

You can get digital infrared thermometers for £20 now , might be a worthy addition to the toolbox.

Well, checked the temp gauge and it's 10c out at the bottom of the scale, 5c out closer to boiling temp.

This was in a pan of water on a camping stove, used a cooking thermometer to check against and a infrared gun to check the cooking thermometer (the infrared just looked through the water at the pans base and gave a false reading!)

The Aluminum radiator is too hot to touch at top hose entry point, but the exit hose and most of the rest of the rad is lukewarm, bordering on cold!

It's not spitting, steaming or boiling. It does push water out of the header tank as it warms, but that might just be me overfilling, the header is large and 6 inches higher than the rad, but it feeds into the engine at what is the lowest point.

I filled the cooling system via the temp sender hole and the little pipe on the topside of the rad, the one that lets the air escape, so I'm pretty sure that system isn't air locked.

What worries me is that, according to the gauge, the rad fan isn't taking the temp done at all.

It seems to push a lot of air through the rad, the rad isn't hot, apart from around the top hose, the hoses show a 10 to 15 degree difference top to bottom.

Car isn't mot'ed, so can't road test and don't want to mot it till I know it won't boil up at the station!

The heater hoses (not silicone) feel much cooler and one of those comes straight from the back of the cylinder head.

3 questions, which make of gauge is reliable? Is fitting the gauge in the top hose OK? What temp will the coolant be as it passes through a 88c thermostat?

Till I get a reliable temp reading, can't really fix any problems, (if I do have one!).

Well that's a good question, no idea is the answer!

I suppose taking it out and testing is the next move....perhaps it's just running on the hole I drilled in the stat to aid air lock removal....?

Quick recap, couldn't understand why the new temp gauge showed 98c, yet most of the rad and bottom hose was cold, even the top hose was still touchable.

Following advice on here (thanks), I pulled the thermostat and checked it.

It works, but opens at, (you've guessed!) 98c!

So this where I say WTF! After buying 2 unreliable not opening at the 88c they should, aftermarket stats, I pay 3 times what a Eurocarpart stat cost at the BMW stealer, to get the genuine thing.

I tested it before fitting, it opened at 88c, only now it doesn't, it opens at 98c! That's after 2 years of sitting in a dry engine, not being used. I always thought that stats worked or didn't?

Still hopefully this demonstrates that the cooling system can cope, it run at 98c and didn't get too hot.....or am I deluding myself?

I've got the standard 2 hose heater, hot feed from the back of the head, cold return to the metal pipe that runs along the engine into the water pump, this pipe also draws coolant from the header tank. Air bleed into header tank from rad top and header tank is at least 6 inches higher than the rad and engine.

So 82c or 88c stat? I want it to be fully open at 88c, past experience has shown the temp listed is the "start to" open, not the fully open temp!

Unfortunately, the cooling system is still at the testing stage.

I'm assuming that the water is circulating correctly, even though the Golf rad has the top hose inlet on the opposite side to the BMW rad, the Golf has both top and bottom on the same side of the rad.

The new gauge seems to be fairly accurate, esp. at the higher end of it's range.

The water pump is quite new and with metal impellers.

I picked on 88c because that's the recommended stat on the E30 Zone M52 engine swap Wicki, that's where I've stolen most of the knowledge from. The stat in the car was an 88c one, so opening at 98c is bit disappointing!

I'm going to bin the adjustable controller and use a 95c to 90c switch, mounted in the bottom hose, the temp gauge is in the top hose.

If the 98c stat was working properly and controlling the temp, then the cooling system should cope, when the fan was running the temp stabilized at 98c, the stats open point.

The fan wasn't switching off however, but that's a different issue, hopefully cured by the switch change.

If I use the recommended stat, which is a 92c one, how will a 95/90 fan behave, will it be running all the time because the stat is keeping the temp at 92c?

My brain hurts..........

Hi, That's absolutely bang on, the stat stops the engine operating too cold and the rad/fan stops it operating too hot.

Colin

If you have room you could stick a viscous fan on the M52 and not worry about the electric fan? Just a thought

Are you sure it's the 'stat and not your test method/measuring device? At 98ºC in a saucepan the water will actually be starting to boil.

The Wahler units (Audi use em too, and yes, stupidly expensive) are about the best and usually last at least 5 or 6 years. All the ones I've had fail have gone the other way and either open too soon or don't fully close. My TDI doesn't generate much waste heat so in the winter even a small gap in the thermostat means it doesn't warm up properly.

Nick