If you are loosing coolant or engine oil on a GM 2.8, 3.1 or 3.4 engine I would recommend inspecting for leaks from the lower intake gaskets. In some cases coolant may intermix with the engine oil due to lower intake gasket failure, this can easily be misdiagnosed as leaking head gaskets. If the engine has been overheated, a carbon test should be performed to see if there is any exhaust fumes in the cooling system, indicating a blown head gasket.
The gaskets that contact the heads are made of a plastic looking composite material, with rubber inserts that are prone to leak. If that isn't bad enough, where the front and rear of the lower intake contacts the engine block, there is only silicone to form a seal. Inspection of the gaskets when they are removed will give you an indication of the source of the leak; look for distortion of the rubber inserts. Inspect the intake manifold for corrosion and pitting, this can also allow fluid to seep past the gaskets.
The 48500 has been discontinued. Click the following for the updated 48300. Although the 48300 is too large to use with the rear valve cover on, it does still save the wear on the threads for the rocker arm bolt.
Below are a few common mistakes that are often made when performing this repair
• Inadvertently damaging fuel o-rings, causing a fuel leak
• Allowing excessive coolant to enter the crankcase, contaminating the engine oil
• Improper placement of the push rods, causing bent valves
• Not really a mistake, however can cost much time is unnecessarily removing components like the alternator, ignition coil, rear valve cover and rockers
• Leaving debris or foreign matter in the engine while the intake manifold is off
• Not cleaning lower intake bolts, bolt holes and applying thread locker to the threads of the bolts
• Using coolant other than Dexcool
• Not removing the old gasket line up tabs
One way to avoid damaging the seals on the fuel supply and return lines is to not remove these lines to begin with. Unbolt the fuel rail and, pull it to the side and use a tie down to hold it out of your way. Be sure to inspect the condition of the fuel injector o-rings and apply some lubricant to help the injectors go back into place when reinstalling. Drain the coolant prior to removing the lower intake, failure to do this will allow coolant to go into the engine crankcase and contaminate the engine oil.
If coolant mixes with the oil it will require several oil changes before the oil will be free of coolant, damage may occur. I recommend using a fluid evacuator section to extract the coolant from the cooling system, by attaching the fluid extractor's hose to the vehicle's water pump by-pass hose the coolant can be sucked out quickly. The push rods go through the gaskets therefore must be removed to replace the gaskets. However the push rods can be taken out without the removal of the alternator, ignition coil, rear valve cover and rockers with the use of a GM push rod removal tool (LIS48500).
If there is not enough clearance to remove one of the push rods with the tool, turn the engine crank slightly to allow for enough clearance. Take note of the order and length of the push rods, the intake and exhaust valve push rods are different lengths, valve damage can occur if they are placed in the wrong position. While removing the old gasket material, use something to catch the debris such as clean shop towels or paper floor mats. Abrasive material allowed to enter the engine can cause premature engine failure.
Foreign matter can restrict the flow of oil through the pick up screen and can cause catastrophic engine failure. Fully inspect for foreign matter prior to reinstalling the intake manifold. Over tightening the lower intake bolts can crush the gaskets, failing to use thread locker could allow the bolts to loosen over time. Always clean the bolts and bolt holes, then apply thread locker, use a torque wrench to tighten to service manual specifications. When replacing the coolant be sure to put Dexcool back in.
Mixing green coolant with Dexcool can possibly cause a gel to form resulting in further problems you don't need. Prior to reinstalling the upper intake, be sure that the line-up holes for the paper gasket are free of old gasket line up tabs. Leaving these tabs in place can cause the upper intake to crack when the bolts are tightened. After reassembly turn the heater on bleed the air out of the cooling system using the bleeder screw on the coolant pipe (if equipped) and the use of the Lisle coolant funnel is helpful. Follow up with an oil change, check the the oil for coolant contamination, change oil again if necessary.
Time saving tips for changing GM intake gaskets without removing rear valve cover, alternator and coil, the specialty tool is simple and easy..
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