Diesel overheating with normal temp gauge...

[dr. no]

After the recent rebuild saga (http://www.thesamba.com/vw/forum/viewtopic.php?t=585693), i was back on the road... briefly. (1.6td, JX engine meant for German Vanagons)
Intermezzo included having the wrong size rings and bearings delivered by otherwise reputable local and national suppliers (something for a different, whining post). I got quite good at whipping the oilpan off and on...
Then setting the timing etc went well and it ran! Quite nicely, smooth, more power up and down the driveway (it's half a mile to the mailbox) and beyond. Tonight I took it further, about six miles downhill, no problems that a little idle adjustment/smoke screw shouldn't fix. Then, halfway home: loosing power, normal coolant temp and EGT. Pulled over, would not idle and shut off. I noticed steam coming out the vent, and went to look... boiling coolant. The alternator/pump belt was tight enough and the pump pulley turns when turning over.

I haven't disassembled yet, but, assuming the sender is working (and it went to it's normal place, just below the LED), overheating covertly should mean the water pump isn't pumping. How else? No hose leaks or other leaks. Also, not coming out through the reserve tank, although plenty of pressure, so probably a bad cap on the pressure tank. Bad head gasket or any other internal leaks, if the pump were pumping, would deliver hot coolant to the sender, right?

How to prevent covert overheating? I think that a burst hose did this to my original head in the first place, so I'm tired of it. Oil temp gauge as a backup?
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Scott
http://lungehphoto.com

'83.5 Westy s/p 1.6td JX and 4sp DK transplant--wonderful!
'86 MB 300GD
'06 MB Sprinter
'17 BMW X1
'89 Isuzu Trooper


PAST VWs:
'82 NA diesel Vanagon
'86 7-passenger Vanagon
'77 Bay
'71 Bay
'74 Things (2)
'69 Karmann Ghia (the only one I miss--in nice weather, anyway...)
'91 Fox

[bluefirefly]

Is it possible you still have air in the cooling system and your coolant pump isn't "moving" anything?

Sorry, only guessing as I never worked on a TD before....
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86 Syncro Tintop G60
work in progress ...as always!

[danfromsyr]

the sender only records the temperature at the point in the system.
if there's no water but only steam there it'll show ~212*f, very happily in the middle of the gauge.

I'd say you likely have air in the system or an incorrect coolant flow path.
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[atomatom]

does the radiator get warm?

is it cold on the top (air) and hot on the bottom?

is it all cold? then either pump is dead (unlikely, i think they make lots of noise when they die) or perhaps the thermostat (not opening).

another option is you have a leak and the system is not holding pressure. do the hoses feel firm (like bike tire inflated firm - or rather, half that).

not a bad idea to buy one of those laser/IR thermometers then you can point it at stuff and see if it is the right temp. but the hand test should work on the rad.
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84 Vanagon Westy, 1.9L, California raised but defected to Canada.

[dr. no]

Thanks! More brains are better than one.

The lack of water may be the issue, but I doubt it. I didn't mention: at the bottom of the hill I had topped off the pressure tank (a pint or less). This is about what I expected, from prior flushes. The fan had kicked on (normal for climbing the hill) so there was warm water getting to the front. It also turned off soon, so there wasn't much staying there.

As I said, it was holding air/water/steam, no leaks. Also, no water in oil, or oil in water.

I'm leaning toward a head gasket leak, or failed pump. It was of the stamped sheetmetal fin type, not cast metal or plastic. It happened rather quickly, with no overheating on the gauge.
_________________
Scott
http://lungehphoto.com

'83.5 Westy s/p 1.6td JX and 4sp DK transplant--wonderful!
'86 MB 300GD
'06 MB Sprinter
'17 BMW X1
'89 Isuzu Trooper


PAST VWs:
'82 NA diesel Vanagon
'86 7-passenger Vanagon
'77 Bay
'71 Bay
'74 Things (2)
'69 Karmann Ghia (the only one I miss--in nice weather, anyway...)
'91 Fox

[narendra.vw]

Causes for over heating in TD engines,

1. Air trapped in cooling system.
2. Pressure tank cap's pressure is not working.
3. Radiator fan not working, fuses, rheostat or relay
4. Head gasket loose or bruned.
5. Wrong timing with timing belt.
6.Wrong fuel Pump pressure.
First check,
Open the cap, start the engine & see if coolant is coming back(with out air) through the small pipe connected to the tank. If yes, then coolant pump & circulation is perfect .
Second check,
Keep the engine running for few minutes until temp reading reaches mid way. Now, fan should switch on, If not check fuses, rheostat or relay.
next, change the cap for the new one.

[danfromsyr]

you opened the pressure tank and added a pint to top it off.. but what about the coolant level in the radiator? did you bleed/purge air?
it's quite possible you were still quite under full on coolant..

[MarkWard]

From memory, it takes about 3 gallons to fill an empty system. How much coolant did you put in? Next, two tips when filling the cooling system on a diesel. One, remove the discharge hose from the head and fill the engine to the brim with your coolant mix. The thermostat will not open if the engine has not coolant in it. I always drill a 1/16th to 1/8th inch hole in the thermostat to help the engine from getting air bound.

I would also add, my diesel takes miles to get to temperature with a properly working cooling system. For yours to overheat in such a short distance, it sounds like the engine had no coolant in it.

Someone also mentioned the cooling house routing. It is possible you have mixed up the main hoses too and from the front. Coolant flows into the bottom of the radiator and out the top. This is opposite of most vehicles. If your last engine blew a head gasket, you may still have a problem.
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☮️

[dr. no]

First look:
--No leaks
--I could not tighten head nuts any more (I did not quite get the full last quarter turn after warm-up, too hard!)
--timing belt is intact, turns over by hand without bad noises, static timing remains where I set it (1.00)
--turns over with key but sounds like something rubbing -- belts look ok and oil pressure light goes out while cranking, stays out for longer (than I was used to with old pump) after stopping
--caught and ran for a minute, but then the battery gave up.

It's looking like there was perhaps not enough coolant, though I put in over two gallons, the radiator was warm enough for the low-speed fan to come on. When this had a gas engine, I always had to purge many times from the radiator bleed. Since conversion, I have only needed to run it a little, top off and repeat a couple of times. The diesel hose configuration works (ed) better.

Why would it make any significant difference which way the water goes through the radiator in a pressurized system? It's not a thermosiphon, there is always a pressure gradient. The only difference I see is that filling from the bottom would help obviate the need for bleeding at the radiator, as air would be purged back to the tank (or perhaps to the pump to cavitate).

And for distance to warm up, we live at almost 8000 feet, almost 1000 higher than town (Santa Fe). When I say "hill" it's more than the altitude difference between Houston and Dallas...
_________________
Scott
http://lungehphoto.com

'83.5 Westy s/p 1.6td JX and 4sp DK transplant--wonderful!
'86 MB 300GD
'06 MB Sprinter
'17 BMW X1
'89 Isuzu Trooper


PAST VWs:
'82 NA diesel Vanagon
'86 7-passenger Vanagon
'77 Bay
'71 Bay
'74 Things (2)
'69 Karmann Ghia (the only one I miss--in nice weather, anyway...)
'91 Fox

[MarkWard]

[atomatom]

on my van one of the hoses was pinched under the spare tire in the clamshell. i'm not sure how common that is, but i suspect it didn't help matters.

the water routing makes sense - hot water moves up. there is a large amount of water to move around in a vanagon.
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84 Vanagon Westy, 1.9L, California raised but defected to Canada.