Kurt

New head gasket I fitted was leaking!! Possibly because I had missed water in the bottom of some bolt holes in the block..... i did think some of the bolts felt a bit springy as I was torqueing it down. Checked head and block faces with an engineers straight edge whilst it was all apart again and both were good to go just gave the block face a carefull going over with 2000 grit paper. After a couple of days of running all seems fine.

Managed to fit the new head today. Was plenty of fun in sideways hailstone! Took her for a short drive and all seems well regarding combustion escaping into coolant. though I was running out of light by the time I had finished so I shall have a thorough check tomorrow. Seemed to take far longer in the cold putting it back on than I recollect last time I did the headgasket. To many retreats inside for coffee this time around possibly! What I am definitely aware of however is that the backpressure at the air filter still remains......

Hi Nigel, EGR removed last year on mine.

Neither does mine! Intercooler pipe off and theres a definate strong vacuum at the inlet. Same if i disconnect inlet pipe from turbo but when i reconnect it the pulsing begins again at the filter box. As mentioned already perhaps some kind of turbulance generated inherit to the intake design is the only other reason i can think of. Im quite intrigued by how many other tdi's may be showing this quirk/symptom. I dont think i would of noticed to be honest if the little rubber cap thingy hadnt of been missing off my air cleaner.

Not sure what to do with the old head. May get it checked and keep as spare ( they may get rare one day! ).

I did fit new valve stem seals a couple of week ago as i was getting quite a bit of smoke on idle which cured the problem. three of them were in quite a state. Maybe that could explain the difference in the ports?

^ Just lightly oily/dark. No sludge build up as I cleaned them the last time head was off. Piston tops , injector nozzles and glow plugs look fine.

Sorry forgot to add that inlet ports 3 and 4 were also noticeably cleaner than the others?? Exhaust ports were uniform in appearance front to back.

Quick update Head off today and gasket appears to have failed ( but not in a spectacular fashion) between water gallery and no.3 cylinder. Also plenty of oil around pushrod area on block surface but not certain if this is just spillage whilst removing head. Have opted for a new head and its waiting , all shiny .to be fitted on my workbench . Had a minor panic refitting injectors to the correct spec as per workshop manual as one just point blank refused to torque up! After much head scratching it became obvious on inspection that the injector stud was stretching itself into an hour glass profile! All at around 15nm! must be made of cheese. Whipped one out of the old head (which I was a bit weary of re-using at first with all the horror stories of these snapping) and it tightened up just fine.

Thanks Mo. Job for tomorrow evening! I'l keep this thread updated as to what i may find. Thanks all for the suggestions , helped keep me motivated and determined in pinpointing the problem and thankfully before something went pop!

Head/head gasket has gone! ​Noticed that it sounded a little extra raucous ​today and was a bit of white smoke upon acceleration away from lights this morning. Just checked the header tank and the new ( blue) coolant i put in at weekend has turned a sickly bright yellow colour! No bubbles at idle ( perhaps why i did not notice it earlier ) but a steady stream when rev'd. Had put a new mls gasket on it a year ago and it had been fine until now. Think i may have found my problem!

^ Standard ( just replaced ) air filter with snorkel. Noise still present with snorkel disconnected.

I was mistaken. Arfter driving again today the booming is still there....

Went for a drive today and the booming under load appears to have gone after replacing manifold gasket ( showing evidence of leaks around inlets) and intercooler hoses which were very soft with a light misting of oil around the end of one of them. Timing case off also and belt perfectly aligned when all the pins are in. Backpressure remains however!

^ Actually I just had the thought that it may possibly be a seized/sticky/otherwise damaged cam follower or other part of the tappet assembly? Might be worth checking before I remove the head.

Other thing is exhaust/inlet gasket leaking between exhaust and inlet port. New gasket fitted today all bolts/nuts torqued to correct spec and still backpressure in the inlet..... looks like the head is going to have to come off. Oh the joys!

Oh it does that most definitely unfortunately.... when under load and I can kind of drive through it most of the time conditions allowing. More of an annoyance than anything though I might just be able to detect a bit of flatness in power when it happens and sometimes with a little grey/whitish smoke to. Thanks Les have tried the oil filler cap off and still the same! Beginning to think more and more that this is a valve timing issue as pulses of backpressure became more defined ( more of a definite "pop" than slightly pulsing draught of air ) after I changed the timing belt. One thing that has played on my mind after doing the belt change is that I developed a bit of confusion over the cam timing in that are you supposed to time exactly to the mark on the sprocket or to the peak of the tooth? The marking on mine was more to the shoulder of the tooth kind of in between the valley and the peak?

^ Thanks for the suggestion it was something that had not crossed my mind though should have. All seems well with the rocker assembly ( whipped the cover off and removed/refitted this evening). One more thing of note is that if I remove the top intercooler hose I can hear a definite kind of metallic "popping" noise coming up through the inlet manifold and what sounds like a bit of disruptive turbulence being caused in there somewhere. Sounds "exhaust"y somehow for want of a better description. I'm beginning to think burnt seat/sticking/bent valve or a crack between an exhaust and inlet port though not sure how common this is on a 300.

A while ago whilst servicing my defender i noticed that there was positive pressure at the airbox on my defender ( felt at the airbox where the little drain plug fits ). Have recemtly changed the timing belt and the symptom still remains though has become a little more rythmic , 7chuffing around two times a second. Valve clearances have been checked and adjusted along with new valve caps. Timing belt fitted correctly and checked twice since to ensure all still aligned. Runs at correct temp and no bubbles in header tank. Exhaust note possibly sounding a little boomy at higher revs under load. Also pressure definately not coming from crankcase as have disconnected breather from intake and symptoms remain.A little perplexed by this now and amy thoughts on what could be causing this much appreciated.