Thirsty Posted June 20, 2016 Share Posted June 20, 2016 Morning all. Apologies if this has been asked/answered before and I just missed it but I need help! In brief, Mk3 GT6 initial oil pressure on start up/cold running is good and where I think it ought to be (cold idle about 60 psi), within 10 minutes of driving and at steady cruise, I notice the needle sweeping round the guage as the pressure drops. It gets down to about 15-20 psi with no real noticeable difference between idle and revs. I'm using a 20W50 oil currently. Am I just being a bit paranoid and this is acceptable? It just seems odd the way the guage drops, almost comically like the classic aircraft fuel guage in a cheap disaster movie! Any ideas? Quote Link to comment Share on other sites More sharing options...
Clive Posted June 20, 2016 Share Posted June 20, 2016 What 20/50 oil? Some is horrific, some very good.The constant low pressure with no increase is worrying. May be worth investigating the relief valve as a first check. And also beg/borrow/steal and alternative gauge to check that too. Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted June 20, 2016 Share Posted June 20, 2016 Electric gauge or capillary? If electric then it may be an instrumentation issue.The odd part is to get little change as revs increase. 15 - 20psi at hot idle is a little low but perfectly ok for a well used engine. However, it should come up smartly as the revs rise and reach at least 40 psi by 2000 rpm. As Clive says it may also be worth checking the relief valve - possible broken spring?Nick Quote Link to comment Share on other sites More sharing options...
glang Posted June 20, 2016 Share Posted June 20, 2016 I cant see it being a relief valve problem as the pressure does reach 60psi when cold so the spring must be good. I think its more likely to be worn crank bearings/oil pump and wonder how miles its done? Ive just done both on my vitesse at only 65000 genuine miles with the engine in the car and using the uprated oil pump. I caught the bearings just at the right time and now Im getting a decent pressure even on hot tick over Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 20, 2016 Share Posted June 20, 2016 You don't need an "uprated" pump. My GT6 has a standard pump and filter, and reaches 95psi at 3500RPM cold, still above 35psi stinking hot idle. I do use half-decent oil, and the pump was set to factory tolerance when I rebuilt the engine... in 1993.I'd say the rapid drop-off with warming up could be very poor quality oil but the absence of noticeable difference with speed suggests an electric gauge where the sender is actually a temperature sender rather than a pressure one Quote Link to comment Share on other sites More sharing options...
RedRooster Posted June 20, 2016 Share Posted June 20, 2016 Quoted from cliftyhanger What 20/50 oil? Some is horrific, some very good.. What do you think of the Halfords 20/50? i usually give it a squirt of extra ZDDP just to be sure.RR Quote Link to comment Share on other sites More sharing options...
Clive Posted June 20, 2016 Share Posted June 20, 2016 Never used it, but should be OK as long as the car isn't driven hard. Not a performance oil (ie trackdays) and I think has a shortish life? Quote Link to comment Share on other sites More sharing options...
glang Posted June 20, 2016 Share Posted June 20, 2016 Quoted from RobPearce You don't need an "uprated" pump. My GT6 has a standard pump and filter, and reaches 95psi at 3500RPM cold, still above 35psi stinking hot idle. I do use half-decent oil, and the pump was set to factory tolerance when I rebuilt the engine... in 1993.I'd say the rapid drop-off with warming up could be very poor quality oil but the absence of noticeable difference with speed suggests an electric gauge where the sender is actually a temperature sender rather than a pressure one My original pump was out of tolerance and the cost difference of the bigger one is negligeable so I wacked it in, after all you cant have too much oil can you? Has your GT6 got an uprated oil relief valve spring cos my manual says the standard one should dump at 45 - 55psi..... Quote Link to comment Share on other sites More sharing options...
efp Posted June 20, 2016 Share Posted June 20, 2016 Maybe a non- sequitur, in which case apologies, but wanting to fire up my 1147 lump after a 23 year hibernation followed by a rebuild, I decided to replace the temp gauge with a Smiths dual temp/oil pressure jobby, as I had otherwise nothing but the pressure warning light which I wasn't totally confident with. Early days yet, but Im seeing 60-ish psi on cold idle, dropping to 40 ish when warmed up, but this is static, yet to take a road run. Not unhappy.Cant tell you what a buzz it was to hear that burble again after all those years.. First turn of the key too. My point is, while fitting the (plastic) capillary oil pressure tube, I can't be entirely sure I expelled absolutely all air from the line before clamping it all up, despite my best efforts. Maybe theres some trick to this but I can't find it documented. So I'm wondering if, should there be an air bubble in the capillary tubing, will it not expand as the oil and engine bay warm up, and have more compressibility, throwing out the numbers?Sorry if this is a dumb question Quote Link to comment Share on other sites More sharing options...
JohnD Posted June 20, 2016 Share Posted June 20, 2016 No need, efp, no need!The air in the line will compress quickly and transmit the pressure to the gauge. A little oil will travel up the line as it does so, but a tiny, insignificant amount.As any air warms and expands, some oil will travel back out and equilibrate the pressure.It's all automatic!John Quote Link to comment Share on other sites More sharing options...
efp Posted June 20, 2016 Share Posted June 20, 2016 Thanks for your advice and reassurance John. Feeling more confident now. cheersJohn Quote Link to comment Share on other sites More sharing options...
Thirsty Posted June 21, 2016 Author Share Posted June 21, 2016 Sorry for the radio silence and thanks for the comments!The oil is a Carlube Classic 20W50 and the guage is capilliary. The engine has 85k original miles and runs sweetly without any knocks so I hope we're not talking bearings! My first thought was sludgy deposits in the oil so was thinking of dropping the sump and giving it a good clean. I have a new pump for it so will fit that at the same time. Maybe before that I will renew the PRV spring and blow through the oil line to the guage. I've just thought of something whilst typing. I changed the oil a couple of hundred miles ago but the motor factors sent the wrong oil filter element. I had to put it back together with the old one in whilst waiting for the correct one from Rimmers but haven't swapped it yet. Could the most obvious solution be staring me in the face? Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 21, 2016 Share Posted June 21, 2016 I've found the Carlube stuff to be weak as piss and deteriorates to the point of unusable in a hundred miles or so. Certainly did on Tessa. Change it. I used Penrite ("light") this time and it transformed the oil pressure.Quoted from glang Has your GT6 got an uprated oil relief valve spring cos my manual says the standard one should dump at 45 - 55psi..... As far as I know it's a standard relief spring, but the previous-but-one owner may have uprated it in a misguided effort to fix the oil pressure problems resulting from the timing chain having disintegrated and left shards of sharp hardened steel all through the oil system. That was why I rebuilt the engine in '93.Once fully warm, I do get a fairly good, steady 60psi in normal driving, so I think the relief valve is probably opening when it should but just not flowing enough to dump the cold pressure. Quote Link to comment Share on other sites More sharing options...
glang Posted June 21, 2016 Share Posted June 21, 2016 Quoted from Thirsty Sorry for the radio silence and thanks for the comments!The oil is a Carlube Classic 20W50 and the guage is capilliary. The engine has 85k original miles and runs sweetly without any knocks so I hope we're not talking bearings! My first thought was sludgy deposits in the oil so was thinking of dropping the sump and giving it a good clean. I have a new pump for it so will fit that at the same time. Maybe before that I will renew the PRV spring and blow through the oil line to the guage. I've just thought of something whilst typing. I changed the oil a couple of hundred miles ago but the motor factors sent the wrong oil filter element. I had to put it back together with the old one in whilst waiting for the correct one from Rimmers but haven't swapped it yet. Could the most obvious solution be staring me in the face? Hi thirsty, yes definitely tackle all the easier obvious options first. However if you do decide to take off the sump (which will probably require the engine mounts undoing to lift it up a few inches) why not inspect a bearing or two while your at it? Big ends usually wear fastest and you might just see the copper underlayer beginning to show through the white metal. Of course cleanliness is essential as is putting everything back as was and with correct torques... Quote Link to comment Share on other sites More sharing options...
Thirsty Posted June 22, 2016 Author Share Posted June 22, 2016 Quick update. Changed the filter element last night (the old one hadn't been on very long by the way, which was why I wasn't too concerned about leaving it on) and ran the car up to full temperature. What a difference. Hot idle was a little up (about 20 - 25 psi) but the marked change was the increase when upping the revs to 2k (45psi). I'm happy with that! That will certainly make this seasons usage a little less uncomfortable. I'll still get it on the ramp and drop the sump in the winter as there is less urgency now and try some of that Penrite stuff RobPearce. Can anyone recommend where I might get an original filter element (Lucas?) from as I'm not overly impressed with the stock I have? Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 22, 2016 Share Posted June 22, 2016 The original GT6 oil filters are getting hard to source but I've not actually had any problems with ones bought off eBay or ordered in via local motor factors. One thing to beware of may be the glued-on gaskets - certainly there were problems with Unipart oil filters for Stags / Dolomites / TR7s at one point with them coming unstuck and sliding across the oil passage... with predicatbly unfortunate results. Quote Link to comment Share on other sites More sharing options...
daver clasper Posted December 21, 2023 Share Posted December 21, 2023 On 20/06/2016 at 17:16, glang said: I cant see it being a relief valve problem as the pressure does reach 60psi when cold so the spring must be good. I think its more likely to be worn crank bearings/oil pump and wonder how miles its done? Ive just done both on my vitesse at only 65000 genuine miles with the engine in the car Hi Glang. Was the sump ok to remove, with jacking the rear of engine up a bit/some?. I've heard it can be very difficult. Any tips please Quote Link to comment Share on other sites More sharing options...
glang Posted December 21, 2023 Share Posted December 21, 2023 Hi Dave, it was a little while ago now although I remember it wasnt the nicest of jobs but not so much for difficulty as comfort. The car needs to be high enough off the ground for access but you then have to lift engine to get the sump out. This has to clear the oil pump pick up so I released the engine mounts and jacked engine up which was then supported on wood blocks to the chassis. An engine hoist would be better but my method worked so I could then remove the jack and undo the sump. Maintaining cleanliness is not easy but essential. It was well worth doing though as the main bearings were just going through to the copper under layer and its also nice to now have the upgraded oil pump... Quote Link to comment Share on other sites More sharing options...
Clive Posted December 22, 2023 Share Posted December 22, 2023 Top tips for sump removal. Drain the oil, and leave the car for a day or 2. That way you are less likely to need to pressure wash your hair with truckwash. A hat is a good idea too. Better, a shower cap! 1 Quote Link to comment Share on other sites More sharing options...
Tim Bancroft Posted December 22, 2023 Share Posted December 22, 2023 Clive, good advice...however if bald, not such a problem!!!!😂😂 2 Quote Link to comment Share on other sites More sharing options...
glang Posted December 22, 2023 Share Posted December 22, 2023 Draining sump very good idea but I dont remember having to angle it so steeply as to get residual oil on my head😳 Quote Link to comment Share on other sites More sharing options...
Clive Posted December 22, 2023 Share Posted December 22, 2023 6 minutes ago, glang said: Draining sump very good idea but I dont remember having to angle it so steeply as to get residual oil on my head😳 More that oil will drip from the block once he sump is off. Hence drain, then leave so it all drips off into the sump Quote Link to comment Share on other sites More sharing options...
glang Posted December 22, 2023 Share Posted December 22, 2023 Oh yes definitely lots of rag to wipe off all the inside of block and crank before starting work. Then glasses while working👍 Quote Link to comment Share on other sites More sharing options...
daver clasper Posted December 23, 2023 Share Posted December 23, 2023 Thanks guys. Not an urgent job I don't think. though something I may attempt in the future Quote Link to comment Share on other sites More sharing options...
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