Radiator Strangeness

[RJBingham]

Hi all, my 1.6 hdi is normally rock steady temperature wise, sits just under halfway on the gauge when warmed up, noticed it was a bit warm yesterday, put the heater on and it immediately dropped back to normal, but after checking I noticed one half of the rad was hot (the side with the hoses), but the other side was stone cold, after leaving it parked, engine off for about half an hour, the radiator was warm all over, as if the hot and cold sides had mixed, driving it again resulted in the hot/ stone cold division again, not losing any coolant, I'm thinking, maybe a blockage in the radiator?
any insight appreciated.

[Sol]

Water goes into the rad hot and comes out cool, which is the function of the radiator and fan. Then when you switch off and the pump & fan stop, then heat soak takes over and the temperature evens out all across the radiator. It's called thermal equilibrium or entropy.

It's meant to do that.

[RJBingham]

So for the right hand side of the radiator to be stone cold, and the left hand side to be red hot is normal?

[Sol]

It's usually top to bottom where the biggest gradient is found, but the exit side (where the bottom hose is) would be much cooler than the entrance side, and that is normal. If your radiator was fully blocked between one side and the other, water wouldn't flow and the engine would boil over like a kettle.

It has to flow from top right to bottom left say (can't remember which side is entrance and exit on the M59) so it should actually look like a pair of of triangles on a thermal camera, with the apex of the hot one being the entry hose. I can take a picture with my thermal camera once my B9 is up to temp, may be a bit different from yours but I'm sure a blockage (even a partial one) would be very evident in the final temperature on the gauge from the reduction in cooling volume and surface area.

If you do have a few blocked channels, I can't see the whole side being cold, but more hot / cold / hot down the exit side. Is the expansion tank murky?

[RJBingham]

Hi again, no the coolant in the expansion tank seems fine, it's strange, there is a definite dividing line between the cold and hot sides of the rad, almost as if someone had drawn a line down the middle!

[Sol]

Weird. That would almost be the perfect radiator when it comes to getting rid of heat! A near perfect thermal gradient from 90 to 20 for example.

Ok, a couple more questions, does the engine fan run constantly and does it maintain just under 90 on the gauge once warmed up and driving.

(In normal circs it will drop to between 60 and 70 perhaps, if left to idle. HDi engines like most modern diesels are very thermally efficient)

[RJBingham]

Thanks again Zion, well I've done a couple of hundred miles today, and it's been fine, the fans aren't on, and the temp gauge has been just under 90 most of the time, still the left side stone cold and the right side very hot, but I guess it's doing what it needs to do, thanks for taking the time to help, much appreciated, any more funny goings on I'll be looking for your insight again.
Thanks, once again

[Sol]

No worries! Glad to help in any way if I can.