John Comber Posted June 10, 2014 Share Posted June 10, 2014 Question, please o learned forum, my GMC has recently lost water into the sump, head gasket changed, which the old looked suspect across an oil/ waterway . Fully flushed, 20 miles later, same problem, runs perfect , no pressurisation in cooling system beyond normal.Did a cylinder leakage test at both TDC and BDC , no air escaping into cooling system there, so now stumped :banghead: Before I purchased had sat for a few years, so wondering if the head has split/ cracked between ways to allow oil to sump, thought I would get the head crack tested or x rayed but told by two local companies this is no longer done ? Is there anything I have missed or could do :thanx: Quote Link to comment Share on other sites More sharing options...
Gordon_M Posted June 10, 2014 Share Posted June 10, 2014 Well, the block and head could be Magnetic Particle checked or Dye Penetrant checked - no big deal. However your block may have cracked internally where you just couldn't see it. Long term solution is pull the block strip the crank and pistons out, leave the head in place, fill the water jacket and pressurise it and look to see where the water is coming out. Short term? I'd be inclined to try a can or two of leak sealer in the block. Even better if you could do that with the radiator out of circuit to avoid blocking that up - connect the radiator inlet and outlet together, throw in leak sealer and water, run it just long enough to get hot. If this was a jeep, the classic location would be a crack from the water jacket into the distributor tube, but no idea where the equivalent weak point is on a 270. I'd be watching out for a good 270 that I could rebuild ready to swap in, too. Quote Link to comment Share on other sites More sharing options...
John Comber Posted June 11, 2014 Author Share Posted June 11, 2014 Many thanks for the advice Gordon M , just another task to add to my list!! , will pull it to bits and let you know. Quote Link to comment Share on other sites More sharing options...
Tony B Posted June 11, 2014 Share Posted June 11, 2014 There are some good 'Glass' block sealears now. They cope with things that would have been a write off a few years back. Quote Link to comment Share on other sites More sharing options...
deadline Posted October 4, 2014 Share Posted October 4, 2014 (edited) Good shops will perfrom hydrostatic test on the heads and block for internal cracks. It cost about $80USD for my G506's 235 bock (the complete inspection was over $300 for magnaflux/pressure and cleaning). You can also pressure test the system yourself. take off the water pump and thermostat housing, fit a steel plate over them with a gasket and bolt them on. Plug the temp probe hole. Add an air nipple to one plate and pressurize to about 20 PSI. Let it sit. Is should hold pressure. If not you have a leak. Soapy water will tell you where it is. Edited October 4, 2014 by deadline Quote Link to comment Share on other sites More sharing options...
deadline Posted October 7, 2014 Share Posted October 7, 2014 Obligatory youtube video Pressure test the head: Quote Link to comment Share on other sites More sharing options...
deadline Posted October 7, 2014 Share Posted October 7, 2014 And the block Quote Link to comment Share on other sites More sharing options...
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