Robert Price Posted May 18, 2019 Report Share Posted May 18, 2019 (edited) Decided to change the oil as I was not sure what the previous owner had in it, bottom end rebuilt apparently about 700 miles ago, pressure was good 20 -25 tick over and 60-65 psi at 2500 rpm about 95 psi cold start up. Put in Vavoline VT1 20-50 and a new Mahle OC 38 filter. Took the car out, pressure when hot 2500 rpm about 80 psi and tick over 55 psi. Checked the relief valve which had been renewed recently seems fine, but an oil leak from the head gasket on the distributor side of engine. Plugs all dry look good colour, no idea why the sudden change, seems much too high to me. Rob Edited May 18, 2019 by Robert Price Quote Link to post Share on other sites
colin3511 Posted May 18, 2019 Report Share Posted May 18, 2019 Rob, Check the PRV again. I had this recently and it blew the oil filter and adaptor seal, spraying oil everywhere. The PRV appeared to be fine but it was binding and not limiting the maximimum pressure. I'd say 75 psi at 2500 rpm and 30 psi on tickover. It should be slightly higher on cold start but not too much, as the PRV will limit maximum. The thicker oil at cold increases the delta P across the PRV, as it can't escape as quickly due to the higher viscosity. Colin Quote Link to post Share on other sites
Nigel Triumph Posted May 18, 2019 Report Share Posted May 18, 2019 Oil pressure specification is 40-60psi at 2,000 rpm when hot. Oil leaks from the head gasket on the distributor side are fairly common with Triumph 6 pot motors. The clamping force from the head studs is centred on the bores, and the edge by the push rods... Not so much. Next time the head gasket needs replacing, use Wellseal along this edge of the gasket and there's a better chance the oil will stay inside the engine. Nigel Quote Link to post Share on other sites
Robert Price Posted May 18, 2019 Author Report Share Posted May 18, 2019 As this has happened straight after an oil change I am wondering if it is connected with the filter, maybe the Mahle OC 38 has no by pass valve? I have not yet restarted it after looking at the pressure relief valve but I will try another filter just in case, but logic tells me it has to be connected with changing the oil and filter and I think I can rule out the oil as the issue, thanks guys. Rob Quote Link to post Share on other sites
Waldi Posted May 18, 2019 Report Share Posted May 18, 2019 New oil is “thicker” than old oil of the same grade. The internalby-pass on the filter should not affect the oil pressure too much, it will flow the same way, but with the by-pass open, it is not filtered. Waldi Quote Link to post Share on other sites
Mike C Posted May 18, 2019 Report Share Posted May 18, 2019 Check the filter matches the characteristics that Mocal, or whoever supplied your spin on adaptor recommends. I've blown a filter off on a cold start, 100+ psi in the garage. Just saved the engine because was watching the oil pressure gauge closely. After that experience I modified the adapter to get more thread engagement with the filter and fitted a Ryco Z37 which has the internal bypass and anti drain back valve. I now get 90 psi on a cold start and I'm happy with that. Quote Link to post Share on other sites
John McCormack Posted May 19, 2019 Report Share Posted May 19, 2019 5 hours ago, Waldi said: New oil is “thicker” than old oil of the same grade. The internalby-pass on the filter should not affect the oil pressure too much, it will flow the same way, but with the by-pass open, it is not filtered. Waldi Agree. Take the car for a good drive, over an hour including some freeway and see what the pressure is above 2000 and at idle. 30-40 at idle and up to 80 psi above 2000 is OK. Don't forget these gauges aren't perfectly accurate. Quote Link to post Share on other sites
Robert Price Posted May 19, 2019 Author Report Share Posted May 19, 2019 (edited) An update, I have looked into bypass valves in Mahle they all seem to have one however pressures differ. the OC 38 I fitted has a pressure bypass of 1.2 bar (17psi), and I discover it is fitted to fork lifts and tractors etc. a Mann filter W724/1 is 2.2 bar (32lbs), so it looks as though there is a fair difference.However just taken the car for a long drive good and hot things have settled down 35 psi tick over and about 70/75 psi at speed so good advice John. Rob Edited May 19, 2019 by Robert Price Quote Link to post Share on other sites
Waldi Posted May 19, 2019 Report Share Posted May 19, 2019 Hi Rob, good you were able to clear the issue. The filter has a resistance (pressure differential) across the filter element which is depending on flow rate, oil viscosity and amount of fouling. To avoid oil starvation to the bearings and other points, the by-pass valve opens when the differential pressure is too high, for example in very cold conditions when the oil is very thick. And with that, a 2nd purpose of this valve is to avoid the filter element will collapse. If the valve opens (which we are not aware of), you basically have a bit reduced oil pressure in the system by the amount of the valve opening pressure. The filters are designed to have the full flow with the valve (most of the time) closed, because when open, un-filtered oil will go to the bearings. Regards, Waldi Quote Link to post Share on other sites
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