5.7 Vortec Help!

Nissanwheeler

Nissanwheeler

Active Member
Joined
Sep 4, 2010
Location
kannapolis NC
Hey guys i got a 99 tahoe thats leaking antifreeze into the oil. The previous owner over fulled the motor with oil and drove it for a while and then he said that the motor started shake terriabley, and he parked it. he said it didnt over heat, missfire, or smoke. so i changed the oil and flushed the radiator and filled it. drove it down the road, it ran great, no signs of a blown head gasket, but when i parked it i checked the oil and there was still anit freeze in it. I read that the 5.7s are bad about intake gaskets going out but could the antifreeze be leaking into the oil from here? I also checked the spark plugs and nothing out of the odinairy. Ive heard of the oil cooler leaking but how would i test/diagnose this?
 
My first thought was intake gaskets or the one of the coolers in the radiator tanks.
 
ok, so how would i test the coolers? and if i replace the intake gasket what eles should i do while im there?
 
Water in the oil is almost definitely the intake gaskets. They are notorious. You will see moisture and possibly rust on the dipstick and possibly residue on the oil cap.

The oil system has more pressure than the cooling system ever has so a leaking oil cooler is a very unlikely way to get water in the oil. Head gaskets could do it when the motor is off and the cooling system still has pressure when it's hot. Same as the cooler, the water has less pressure than the oil system so a leak will usually leak into a cylinder which is visible in the exhaust smoke and a wet plug. You would also have carbon in the cooling system. A cracked head is also possible but would also usually cause compression problems.

Again, I vote for the intake gaskets. The oem intake gaskets use a plastic frame that cracks and breaks down under pressure and the gm antifreeze. They usually break in the front corners and sometime leak externally also. The Felpro metal gaskets are the way to go. Get them from rockauto or amazon.

I have done this job and it's a pain. You gotta do it or the motor is toast. Clean the intake while it's out. If it has not been done yet and you plan on keeping the truck, consider an MPFI conversion while it's apart, especially if you break any of the poppets and or retainers or the fpr was leaking.


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96, 97, 98, 99 were MPFI weren't they?
 
Croatan_Kid said:
96, 97, 98, 99 were MPFI weren't they?
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CSFI on the 350. They had poppet valves vs electronic injectors at the ports. The MPFI fits in the same place but has an actual electronic injector at each port. CSFI works and is pretty reliable just not optimum for performance. Mine went 200k without major issues. MPFI fixes the poppet leak issue but still has the intake flow restriction problem. It works but is not perfect by any means.

CSFI is Central Sequential Fuel Injection. The central module controls the sequence and the pressure. Poppet valves at the end of the spider runners kept fuel in the lines but not under pressure. MPFI fits the same way but the actual electronic control is transferred to the injectors at the end of the spider. The legs of the spider are always at high pressure.


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Gotcha, the spider set up. Still way better than TBI :D
 
I'm replacing the intake manifold gaskets on my '96 5.7 350 right now for the same reason. Most auto parts stores probably sell 2 different Felpro gaskets. Get the more expensive ones with the stainless steel frame.
 
Thanks for the help guys. One more question, the motor doesnt have any oil or coolant in now, would it be worth putting some in there to check compression? Or go ahead and do the intake gasket? Are the 5.7 heads or blocks bad about cracking?

Ok so three questions haha but whos counting.

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They aren't prone to cracking more than anything else. How many miles in the truck? I would just do the intake and get it over with. The gasket set is around $60-80.


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Yep! Had my 98 done at about 68K miles. Didn't seem like much mileage, but it caused the #5 misfire! Luckily, mine leaked into the cylinder, & not the oil.
Before the fix, I could also watch the fluid level, in the overflow jug, continue to drop.:shaking:
 
Nissanwheeler said:
Its got upwards of 200k miles

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Click to expand...
Definitely do the intake gaskets. I am fairly certain they would have been done before.

Look at spider while you have it apart. It's a good time to do it. Delphi FJ10566 is the part. Delco and NAPA also have replacements. Yikes! Prices have gone up. I picked up mine in March of this year for around $220 or so off eBay. If you can't do the spider now, just make sure the fuel pressure reg is not leaking and all the ports on the poppets look clear. If there are any really clean spots inside the intake, you probably have a leak and need to replace it. When you take the spider out, make sure you are careful to not damage anything so you can reuse it. The spider can be done later without messing with the intake gaskets.

Make sure you mark your disty rotor position to body and disty body to intake. If you do that you can probably avoid resetting the cam retard for awhile and save some money. Timing a Vortec requires a high end scan tool or around $50.




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heads are know to crack in them. Dave's Head Shop in KTown ussally keeps a rebuilt pair on the self for like 250 exchanged
 
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