1. Home
  2. Chevrolet Trucks
  3. Intake Manifold Coolant Leak, 88 Suburban

Intake Manifold Coolant Leak, 88 Suburban

88 Suburban, 5.7L w/ AC. There is coolant seeping up between the head and the intake manifold on the engine right front . This is just to the right of the thermostat housing. Manifold appears to be aluminum.

For those of you kind enough to read and/or post to my thermostat message, I thought it was a thermostat leak and thus my previous post about which thermo to install.

The seepage isn't heavy enough to warrant fixing immediately. (Hoses, oil, filters, etc, first) That is, _unless_ it's leaking into the oil too. I don't see any sign of coolant in the oil. Is there an easy test for traces of oil in coolant?

Is this a common leak? If so does it typically just leak out the top? When I replace the gasket what's the chance the manifold is warped?

-RC

R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA

Reply to
R Clarke
Loading thread data ...

I bet it is actually the thermostat neck leaking. For some reason this combination of alum thermostat neck and alum manifold eat gaskets. I change the gasket once a year and it lasts about 6 or 7 months before leaking again. Next gasket change I am going to try a Fel-pro Teflon coated gasket... As far as common well I have had the problem on my burban for about 10 yrs, my previous car (an 1988 GTA) had the problem and the 86 suburban at school has the problem. All have the same engine and same intake so I would think it is a some what common issue (based on 3 cars). I think the newer engines went to an O-ring sealing neck so you may consider upgrading to a newer style. I believe there is a test kit to check for coolant in the oil, check you local autoparts store. In all of the cases I have seen, it is the thermostat neck to manifold leaking so if you actually are seeing the intake gasket leak that is a fairly big deal. You may want to check the torque on the intake bolts (35 ft lb for the intake and 21 ft lb for the thermostat neck). Get yourself a LMC Truck catalog

formatting link
they carry just about everything for the suburban,including replacement foam to rebuild the seats. good luck, mark

Reply to
rock_doctor

It's definitely the intake manifold to head gasket. I cleaned the are and dried it, then pressured it up to 16psi with a cooling system pressurizer (a must have for any serious shade tree mechanic). It's seeing at the very top edge of the coolant passage at the head. The thermostat gasket stayed dry. Probably a few cc's of coolant per hour.

Sheesh. I overlooked this simple first step. I'll give it a try.

How did you know I need seat foam? :-) Actually the seats are good. This old truck was garaged. Even the plastic interior trim hasn't chalked up yet. One crack in the dash so far.

The armrests on the captains chairs otoh are full of this nasty black powder that turns to goo if you try to brush it off. They difinitely need new foam. I think it's the same foam that is used in the headliner. Headliner still looks good (fingers crossed).

-RC

R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA

Reply to
R Clarke

R.C.,

This is a common problem on the older trucks as they age. The intake manifold mating surface is likely pitted right at the corners which is causing the seepage. I just did my 88' last weekend. They normally just leak externally, but better safe than sorry.

BTW, retorquing the intake manifold bolts is a risky procedure. Because loc-tite is used on the bolts when the intake is installed you need to break them loose first, THEN retorque to 35 ft/lbs. As soon as you break em' loose the coolant will leak internally and externally. In essence, the bolts should be completely removed, threads cleaned, holes chased, then reinstalled with a new coating of loc-tite. In all reality, save yourself the time and just do it right.

Doc

Reply to
"Doc"

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.