Folks,

I have a slow but steady loss of Coolant and have to periodically add coolant to the reservoir. There are NO leaks to the ground, none on the frame, engine compartment, etc. I'm thinking about the only place it could be going is into the intake?

Anyone ever deal with this on a 5.7 (or other GM engine) or have any ideas for me to consider before I start 'bustin bolts'? Thanks folks.

mudbug

How many miles on the 350 and has it ever overheated?
Also. the year of the motor would help too, if it is DexCool, that stuff seems to become corrosive after awhile.

How many miles on the 350 and has it ever overheated?
Also. the year of the motor would help too, if it is DexCool, that stuff seems to become corrosive after awhile.



1999, 120k miles, never overheated. It is Dexcool. Thanks.

Check to make sure the weep hole on the bottom of the water pump is not wet. Also on the passenger side of the engine towards the back on the intake you will find where the heater hose goes into the intake. That fitting goes bad on them and starts to leak.

The intake gaskets will need to be replaced, this is a common problem on all vortec V8's. They usually tend to go around 80k-120k miles or so. The 350 is a great motor and the vortec's are even better however this is a common weakpoint on these trucks.

The intake gaskets will need to be replaced, this is a common problem on all vortec V8's. They usually tend to go around 80k-120k miles or so. The 350 is a great motor and the vortec's are even better however this is a common weakpoint on these trucks.


Much appreciate you guys taking the time to consider and reply on this one. I have poured all over this engine, engine compartment, undercarriage and can't find a single drop of Dexcool or any other indication of any fluid leak. Put it on a lift, ran it up on ramps, you name it!!! Did when totally sober and when a "little tight" and still no visible leaks. Looks like it may be time to crack some nuts on the intake. I sure hope it's not a corrosion issue but it's time to find out.

Thanks again, Guys.

mudbug

Yep, my 99 OBS Z-71 5.7 did the same thing around 90k. It was leaking on the drivers side - rear of the block. Just a little, but enough to have to add coolant. It IS a common issue on those engines. I had the dealer repair mine for about $350 and the work was warrantied for 1-year.

My water pump began leaking a few months after that and I replaced it myself. Truck has been fine since then - my brother owns it now.

Much appreciate you guys taking the time to consider and reply on this one. I have poured all over this engine, engine compartment, undercarriage and can't find a single drop of Dexcool or any other indication of any fluid leak. Put it on a lift, ran it up on ramps, you name it!!! Did when totally sober and when a "little tight" and still no visible leaks. Looks like it may be time to crack some nuts on the intake. I sure hope it's not a corrosion issue but it's time to find out.

Thanks again, Guys.

mudbug

Three common things leak coolant on the vortec 350...
the most common by far is the intake gaskets...
water pump and coolant nipple would be the next best bet...

If I were a betting man though, I would say that your intake gaskets are leaking on the back side of the motor...not a bad job at all...
if you're reasonably handy, you can have that job done in 3 hours..

Again, Gents, many thanks to all of you. I still haven't gotten to it. Katrina put a lot of things on hold.

mudbug

If you DIY the intake... make sure you re-install the distributor EXACTLY as it came out.... more than 2-4 degrees off either way will set service soon light... Dist on these are only for spark distribution, actual spark timing comes from crank sensor
And yes, dexcool is corrosive, especially on plastic pieces, which BTW are what the intake gaskets are, rubber inserts set into a plastic carrier
And check heater core, leaks there come out the A/C drain

If you DIY the intake... make sure you re-install the distributor EXACTLY as it came out.... more than 2-4 degrees off either way will set service soon light... Dist on these are only for spark distribution, actual spark timing comes from crank sensor
And yes, dexcool is corrosive, especially on plastic pieces, which BTW are what the intake gaskets are, rubber inserts set into a plastic carrier
And check heater core, leaks there come out the A/C drain



Whoaaaaa, Ockgator!!! I didn't think about the htr core drain. That's hope beyond hope but I'll check it out for sure. thanks, man. Thanks all.

Mudbug