Symptoms. A couple of month ago I noticed that my 300tdi engine was showing warmer than normal on a long run. Not into red, but up on normal position. Since then it got gradually worse, now going to ¾ mark on long trips. Engine has had nothing serious done for years, oil change, new filters etc last Oct. Complete chassis/bulkhead rebuild last year, but engine untouched, just lifted out, put back in. About 1k miles since chassis change. I've owned it for 7 years, no problems with heating before, apart from p gasket leak 4 years ago.
No apparent coolant loss. 50% antifreeze.
System not over pressured (no sign of head gasket problem), in fact it rarely seems to have any significant pressure.
Heater fine.
Rad not hot, apart from chamber between top and bottom hoses. No real sign of any flow through it.
1. Unclipped hoses, ran water through everything, backwards forwards etc. Refilled, bled (Fill to both bleed screws, then until water flows from heater return). Took for a run, no different.
2. Took out thermostat, tested, seems fine. Put back, bled, took for run, no change.
3. Changed rad. (New one), filled with 100% water, no antifreeze. Bled. Run, no change (new rad shows same as old, warm between hoses),
4. Removed stat. Bled. Long run, no overheat, but no real heat, obviously. Rad gets warm all over.
5. New stat fitted. Filled with 50% Antifreeze, Bled. Long run, no change, overheat back.
6. Changed sender. Bled, long run, no change.
7. Checked earths with meter, all great as newly made on new chassis/bulkhead. Earth straps on engine and gearbox to chassis, battery earthed to gearbox.
8. Substituted temp sender with resistor (about 330 ohm) to replicate hot engine. Resistor from normal connector to engine earth. Gauge stays steady, no increase when engine on, heater fan run, or any other electrics run. Long run, needle stays steady. Reconnect sender as normal, temp high.
9. Removed bleed tubes and ejector thingy. All looks good, checked that all spigots are clear and not blocked, replaced assembly with new, just in case. Bled. Run. No change.
10. Removed water pump. Looks good, no broken fins, tight on shaft, no gunk around that may indicate blockages anywhere. Bearing fine, nice and smooth.
11. Ran water through head, block, heater matrix, all seems good.
12. Replaced pump anyway, and P gasket. Bled, run, no change.
13. Old sender tested (suspended in pan of water, attached to normal wiring and engine earth). Pan heated slowly, At 88c gauge shows correct temp, 98c it goes to ¾ mark. Tried with engine off, and running. No difference on gauge, just shows water temperature in pan.
14. Water System pressure tested. Removed bleed pipe from Stat housing, blocked pipe with bolt. Fitted Tyre valve to an old pipe, then fitted it to Stat house spigot, pressurised system to 17psi. It kept pressure for an hour, no change. This implies that the head gasket is fine, and nothing leaks on any hoses. Put back together, Bled, run, no change.
15. Attached new gauge, with new sender, new wiring. Ebay special. Shows temp as expected, no change.
16. Got I/R temp reader. Very useful. Spot checks show that when overheating, the thermostat housing is only half filled with coolant – so of course stat wont open, and no flow through Rad. Expansion tank level increases (probably drops back when not running for a bit)
17. So, as gas getting into system, I changed head gasket. One waterway (small one) blocked with silicon gasket, one head bolt (near bulkhead) damp and slightly rusted, so a slight coolant leak. New gasket torqued down per manual. System filled, bled, test run......no change.
18. So, cracked head or block? Bought compression tester, removed glow plugs, all cylinders checked. Readings between 391 and 413psi. So gasket ok, block ok, no cracks in head in combustion area.
19. Head off again. Took for pressure test. All ok.
20. WTF? Where is the gas coming from?
I think I've tried everything, can anyone think what I've missed? Any wild ideas? Am I being totally stupid?
Sorry for lengthy post, and thanks all for any input!
No apparent coolant loss. 50% antifreeze.
System not over pressured (no sign of head gasket problem), in fact it rarely seems to have any significant pressure.
Heater fine.
Rad not hot, apart from chamber between top and bottom hoses. No real sign of any flow through it.
1. Unclipped hoses, ran water through everything, backwards forwards etc. Refilled, bled (Fill to both bleed screws, then until water flows from heater return). Took for a run, no different.
2. Took out thermostat, tested, seems fine. Put back, bled, took for run, no change.
3. Changed rad. (New one), filled with 100% water, no antifreeze. Bled. Run, no change (new rad shows same as old, warm between hoses),
4. Removed stat. Bled. Long run, no overheat, but no real heat, obviously. Rad gets warm all over.
5. New stat fitted. Filled with 50% Antifreeze, Bled. Long run, no change, overheat back.
6. Changed sender. Bled, long run, no change.
7. Checked earths with meter, all great as newly made on new chassis/bulkhead. Earth straps on engine and gearbox to chassis, battery earthed to gearbox.
8. Substituted temp sender with resistor (about 330 ohm) to replicate hot engine. Resistor from normal connector to engine earth. Gauge stays steady, no increase when engine on, heater fan run, or any other electrics run. Long run, needle stays steady. Reconnect sender as normal, temp high.
9. Removed bleed tubes and ejector thingy. All looks good, checked that all spigots are clear and not blocked, replaced assembly with new, just in case. Bled. Run. No change.
10. Removed water pump. Looks good, no broken fins, tight on shaft, no gunk around that may indicate blockages anywhere. Bearing fine, nice and smooth.
11. Ran water through head, block, heater matrix, all seems good.
12. Replaced pump anyway, and P gasket. Bled, run, no change.
13. Old sender tested (suspended in pan of water, attached to normal wiring and engine earth). Pan heated slowly, At 88c gauge shows correct temp, 98c it goes to ¾ mark. Tried with engine off, and running. No difference on gauge, just shows water temperature in pan.
14. Water System pressure tested. Removed bleed pipe from Stat housing, blocked pipe with bolt. Fitted Tyre valve to an old pipe, then fitted it to Stat house spigot, pressurised system to 17psi. It kept pressure for an hour, no change. This implies that the head gasket is fine, and nothing leaks on any hoses. Put back together, Bled, run, no change.
15. Attached new gauge, with new sender, new wiring. Ebay special. Shows temp as expected, no change.
16. Got I/R temp reader. Very useful. Spot checks show that when overheating, the thermostat housing is only half filled with coolant – so of course stat wont open, and no flow through Rad. Expansion tank level increases (probably drops back when not running for a bit)
17. So, as gas getting into system, I changed head gasket. One waterway (small one) blocked with silicon gasket, one head bolt (near bulkhead) damp and slightly rusted, so a slight coolant leak. New gasket torqued down per manual. System filled, bled, test run......no change.
18. So, cracked head or block? Bought compression tester, removed glow plugs, all cylinders checked. Readings between 391 and 413psi. So gasket ok, block ok, no cracks in head in combustion area.
19. Head off again. Took for pressure test. All ok.
20. WTF? Where is the gas coming from?
I think I've tried everything, can anyone think what I've missed? Any wild ideas? Am I being totally stupid?
Sorry for lengthy post, and thanks all for any input!
Im off to check the tr@cking no....
