Ive been having climbing heat on my 85 300TD wagon recently. I also have a crack on my radiator neck.

Im doubting these are related as I made a quick patch using Epoxy (which i have to redo already) and while it was not leaking the heat still would climb a bit higher than I feel it should.

It seems theres a problem also when the speed gets above 100km/hr (60ish) Its like a flap or something gets shut off and the heat doesn't end up through the radiator or something. I can keep it controlled if I crank the heat in the cab, but the speed issue also affects the heat going into the cab, so i have to drive below 60ish and with the heat on most of the time.

I was wondering if the belt driven pump may be having problems. Any easy way to test it? I doubt its the electrically powered pump as it was replaced quite recently.

Any Ideas?

sounds like a bad headgasket to me. only way I know to check the WP is to pull it and inspect the impeller.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The high temp symptoms are consistent with a pressure leak, which is almost a given reference the radiator leak. The "no heat at highway speeds" is a sure sign of a torn diaphragm in your monovalve.

I would suggest that you pressure check your cooling system, after you install a new radiator.

I wondered how a small pressure leak can cause overheating if the coolant level is still in a good range. Its a slow leak.

I thought if I unhooked the electric pump and disconnected a coolant line somewhere, and if there was coolant pumping out it would mean the belt driven one is still functional.

What is a normal pressure range for the cooling system, and with what could you take the measurement?

Not sure how things are in Canada, but many of the auto parts vendors south of the border will lend a pressure test set.

http://www.handsontools.com/Stant-12270-Radiator-Pressure-Tester-Kit_p_5129.html

Could you quantify "climbing heat?"

One possible way to check the water pump w/o removing it is disconnect the hose and run it into a bucket, also disable the aux coolant pump. Hold the fuel shut off valve so engine can't start and crank the engine. If coolant comes out the WP is pumping.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

"The" hose?

It climbs above the notch between the 80 and 120 unless I turn on th heat

Very consistent with a pressure leak.