jimleshed

Active Member
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!
 
You say "gas" but it still could just be air.
Maybe you need to relook at your bleeding technique.
The TD5 (ok another type of engine), is a right sod to bleed.
You have to hold the reservoir above normal height and rev the engine to open a certain valve.
Other simple thought, I take it the stat is the right way round. silly I know?
Last point, did you check the head for warping as well as cracks?
 
thanks for the reply!
Could be air, agreed. Bleeding follows the book broadly, as described at point 1. Head not warped, engineer who did pressure test confirmed that today. Also, if warped, it would probably show on compression test...
The stat only fits one way. (and I make sure toggle valve is at the top).
 
I tend to either follow the workshop manual (fill thru expansion tank etc) or fill thru rad and stat bungs. During this ongoing problem I've probably tried every refill variation there is out there. Including pipe burping! At a guess I've probably done it 20 plus times in the last 2 -3 months - each with the same result.
 
Thats a very detailed fault finding regime you've been on ... have you tried running the car without the thermostat fitted ?
 
Id be looking @t the m@trix flushing with @ hose h@s @ higher pressure th@n the cooling
system pump. Could do @ quick byp@ss n see if improves things.
 
Thats a very detailed fault finding regime you've been on ... have you tried running the car without the thermostat fitted ?
Yep, early on (4). That was before I realised that the problem seemed to be airlocks caused by extra air/gas. Bleed system, run for 5 miles, stat housing has filled with gas/air, no chance of stat opening. Havent checked that again (run with no stat) recently, to see what happens. May try when i get the head back!
 
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Id be looking @t the m@trix flushing with @ hose h@s @ higher pressure th@n the cooling
system pump. Could do @ quick byp@ss n see if improves things.
Have flushed matrix (once during chassis rebuild last year), and early on in fault finding (flushed everywhere with hose, backwards and forwards)
 
Have flushed matrix (once during chassis rebuild last year), and early on in fault finding (flushed everywhere with hose, backwards and forwards)
Will try matrix bypass when head back on, although cant see how matrix can introduce air to system.
also hope to get gas leak detector fluid to see if the extra gas is inlet (air) or exhaust (burnt fuel)
 
True.
But... raised temp increases water temp/creates steam, which increases pressure in cooling system. My system never seems to pressurise. I can take cap off even when temp just below red after 5 mile drive with just a little bit of pressure let out. (I have pressurised system to check cap, joints etc - took it to about 20psi and left for an hour plus, all fine)
It's very confusing, and I've been working on it for 3 months....
:)
 
True.
But... raised temp increases water temp/creates steam, which increases pressure in cooling system. My system never seems to pressurise. I can take cap off even when temp just below red after 5 mile drive with just a little bit of pressure let out. (I have pressurised system to check cap, joints etc - took it to about 20psi and left for an hour plus, all fine)
It's very confusing, and I've been working on it for 3 months....
:)
 
Stick a capillary temp gauge in it before doing anything else, 40 quid ebay.
Thanks
I've both tested that original gauge is correct, and that sender is correct, both in landy and totally separate - water boiling in pan etc at various temps. Also fitted new gauge (ebay) and sender with totally new wiring (new feed/earth etc). Everything I try shows that reported temp is correct.
 
Thanks
I've both tested that original gauge is correct, and that sender is correct, both in landy and totally separate - water boiling in pan etc at various temps. Also fitted new gauge (ebay) and sender with totally new wiring (new feed/earth etc). Everything I try shows that reported temp is correct.

Then I reckon it might be new head time.
Looks like cheap ones are 200 quid new on ebay, which is chicken feed if it fixes the issue.
 
Then I reckon it might be new head time.
Looks like cheap ones are 200 quid new on ebay, which is chicken feed if it fixes the issue.
The head has been tested, and is apparently ok. Got it back today. But I do still think the head is the problem, seems unlikely to be anything else. Will rebuild when new head gasket arrives...
 

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