First post in a while due to school, and its not a good one..... I noticed that I was having to keep filling my overflow tank recently and decided to see how much was in the radiator, not good. I opened the radiator and it was down about a 20 oz. water bottle, and the overflow was dry...again. I think I'm going to have to replace the intake manifold gaskets this (EDIT) Christmas break. Its a 95 with the CPI injection. I plan on doing a compression test, before I just jump into it to make sure its not the head gasket. I found this previous post LINK, are there any other hints that I could use before I jump into this thing?

Thanks for the help in advance.

 

Only advise I can send your way is use the GRAY ATV on the front and rear of the intake when you install it. You will never have that blow out ever again that is known for the cork/rubber (Pending the MFG of the gasket) gasket that goes there.

 

bump ttt

Alright, in addition to the cold knocking, I'm still losing coolant.

About 2 weeks ago I noticed it was down and refilled it, then drove home for break, it was down again. Changed my heater core and all hoses during break. I drove to work and back Mon-Wed and it was fine. Long highway trip back up to school last night and I lost a bunch of coolant again. I'm thinking intake manifold gasket? Any help/suggestions would be great.

 

How does the oil look?

 

have you checked the water pump to make sure it isn't leaking? bad water pumps can also sometimes make a knocking sound.

 

the oil is normal, no milkshake. thats why I'm thinking intake manifold gasket instead of head gasket.

I replaced the water pump a little less than 3 years ago. it's not dripping out the weep hole either.

it's not leaving any puddles when parked, no clear evidence. No puddle in the passenger floor board (new heater core). I think its leaving via the tailpipe.
Is intake manifold failure common on the CPI 4.3's? My dad's '96 305 Vortec had the intake manifold gasket failure, but our '94 350 TBI Suburban never did.

When my dad's truck had the intake manifold gasket go, it was visibly leaking down the side of the block. I haven't seen any leaking water, it's just dissappearing.

 

check for a white residue around the pulleys, belts and pumps. if so then u might have a pin hole in the back of the rad. in the meantime if u purchase a lesser psi cap it may not push the coolant out as bad. i had the stock 16psi and had a similar dissappearing act. so i pressured tested and it was topping off at 14 psi, so i went with a 13 psi. i hav not had any dissapearing coolant since.

 

my radiator is new too, I just replaced it over the summer due to a leak where the plastic end tank met the radiator body. I have a 16 psi on it now, the stock one said 15 when I changed it out a year or so ago. So everything in the cooling system is less than 4 months old except for the water pump, which is less than 3 years old. Won't going to a lower psi lower the boiling temp? I guess since its winter it wont really matter. I have a 180 degree thermostat, and it usually stays pretty cool.

 

yea its only temp untill u find the problem and then go back to stock.

 

iirc, intake manifold gasket failure is common on the '95+ 4.3s.