Good morning, all. Have an R50 that my son drives, started overheating (about 5 / 10 mins after cold start). Here is what I've done to diagnose so far. I'm I thinking right?

-tested for combustion gas in coolant (negative)
-check oil and coolant (visual inspection, no coolant in oil, no oil in coolant)
-topped up coolant and water (50/50 mix)
-bled coolant from bleed valve on upper radiator hose
-ran engine to test fan (low speed fan not coming on, high speed fan working)

Temperature goes up to 112*c (233*f) and the high fan comes on, however at this point I can hold the upper radiator hose with my bare hand and hold my hand on the radiator.

I'm thinking we need a new thermostat and fan, sound right?

 

forgot to mention, the coolant is the green stuff not the blue stuff (previous owner). I'm planning on refilling with the blue bmw coolant

 

If the internal heaters are blowing warm air it's not a bleeding issue. There is a second bleed screw below the battery as well.

I think it would be unusual for a thermostat to fail closed as I'm sure that's what the springs wrapped round them are for so they fail open.

If your going to replace parts, quality thermostat and gasket is a must, might be worth considering the thermostat housing as others have found they can leak with age, again, a good quality part is needed.

Hope something i said helps lol

 

yes sir, I went back and made sure to bleed the lower screw as well, and the upper one again. The air from the heater (internal) is like fire.

the upper rad hose is not hot. The rad is not hot. Why are these not hot? Anyone know?

 

Also I’ve ordered:

fan
thermostat with housing
Related connecting hoses
clamps

 

May be a blockage in radiator, see if you can flush it out as I think they are known to fail

 

You might need a little more coolant in the tank, then try squeezing the top hose to get the coolant pumping around.

 

Good points, both.

I can see how a block in the rad could cause this. I guess I'm hoping that its the thermostat so that I'd not need a new rad. I know I should prob do a total cooling system refresh here and I normally would, but the timing is bad for other reasons right now. I will get a total refresh eventually.

Your point make me wonder, what is the flow order of the coolant. I'll take a guess: rad, thermostat, block, heater core, pump...repeat

Anyone know?

 

Added about a half gallon of coolant / water mix as I was bleeding it. When I squeeze the top hose I can see the fluid level go up and down in the thermostat housing. Not sure what that means

 

I think when you squeeze the pipe the pump is obviously still going but your restricting the flow, so fluid comes up the tube.

Might still be worth pulling both pipes off rad and stick a garden hose in the top and see if anything flushes out, be better to take rad off so you can turn it to give it a good flush.

IMHO I wouldn't consider any flushes in oil or coolant because you can potentially move a problem somewhere else (just incase you were thinking about it)

If the rads not getting hot it would suggest the water is not going through like it should, but as the heater matrix is on its own little loop, you still get heat.

 

Pulling the radiator would be a good thing, agree. If I’m going to go that far in I’d prob order a new rad and more hoses…🤔

Now I’m thinking, if the tstat is failed closed would the heater core still get hot? Rad get hot? I don’t think the rad would get hot but I’m not sure about the heater core.

I just don’t know enough about the cooling system flow

 

The heater core and radiator are fed off the same side of the thermostat.

I think but not 100%
Throught the head to the stat
Splits of to heater core and rad
Through rad
Water pump
Back to the head.

I have not long replaced all my pump, rad and pipework, thermostat and necessary seals.

You could stick a hose in the top of the rad and see how well it flows out the bottom hose fitting, should give an idea.

 

Gonna give it a go. Waiting on parts.