Alex Recupero

I've been battling a leak on a 5.3L vortec that I just bought with 150K miles from an older guy who restores classic cars. Unfortunately I didn't do my checks because he seemed very trustworthy. Regardless. I've had the oil pan degreased and changed so it's super clean but there is still a leak.

I checked the oil pressure sender to see if it was leaking oil, dry as a bone.

I checked the rear main / flywheel area through the inspection port, dry as a bone.

Oil filter, dry as a bone.

The oil cooler block off plate seems to get tiny tiny amounts of oil on it but doesn't seem to be the source of the leak due to it also being on the other side. I will change that anyway. 5 bucks.

I have seen that the starter motor seems to get wet, at least the bolts that secure it to the transmission do, so it could be the crank position sensor. This is my second biggest suspect and I'm in need of some relief.

The biggest suspect is this ... there was some oil hanging out at the rear of the head... now, I'm not an expert in Chevy engines but from what I've read on a pushrod engine like this, it's impossible for oil to leak from that area through all the coolant and valves and still come out looking like oil. The car doesn't spit smoke from the back, there's no smoke from the engine bay. No steam, doesn't seem to be water in the oil creating some goop, though I haven't taken the valve covers off or anything yet. I've attached other photos as well. I do not / can not afford another 1000 dollar bill to do a head gasket. Lol. Please give advice on what I should do.

Link below for photos

https://goo.gl/photos/tf9Cpjqu2SgHSHfR8

Thanks for all help

.alex

cleveland63b

have you completely cleaned everything off and its returned? From the pics I can't really see anything other than what looks like residue

Greg Rosen

soooo...what was it??

idakiteman

For others that may have found their way to this topic:

Alex said: "the starter motor seems to get wet, at least the bolts that secure it to the transmission do"....also he says "there was some oil hanging out at the rear of the head". He doesn't say which head. However....

As for the leak appearing on starter motor bolts.....no doubt a leaky crank position sensor. That sensor sits above the starter, and has a single o-ring as the entire seal against oil escaping out the bore the sensor sits in. Those o-rings are notorious for deforming and failing early, causing substantial leaking. The exact same o-ring is used on the cam position sensor too, which sits behind the intake manifold & heads, next to the oil pressure sensor. It's at the top rear of the engine behind the "valley" which is underneath the intake manifold. One might say it's "behind the heads" (as Alex seems to describe), since it's rear of both heads and between them. Because the crank sensor clearly is leaking already, likely the cam sensor o-ring is leaking too. The cam sensor leak often fools folks into thinking their rear main seal (or main seal cover plate gasket) is leaking. But before you replace the main seal plate gasket, replace these two o-rings first and see if that doesn't fix the leaking. Very often it does.

A challenge is that GM has no part# for, nor does it sell, just the o-rings (and that o-ring is a custom, non-standard size and a unique material, too). This forces you to buy a whole new sensor when your present sensor works fine but just leaks. But DO NOT GO CHEAP on a replacement sensor...(as in cheapo aftermarket sensors)...you'll regret it, do the whole repair over again. Like knock sensors, aftermarket cam/crank sensor parts (non-GM or AC Delco or Delphi) are notorious for immediately not working or, if they do, failing QUICKLY. But the aggravation is the authentic genuine AC Delco/Delphi/GM parts are spendy, which is a shame when all you need is an o-ring.

But here's a little-known source for that unique o-ring: https://www.ebay.com/itm/17397410128...MAAOSw5SRfFbVI

Hope this helps.