I have a 91 convertible with 138,000 mile. I just noticed a little coolant leak last week. Today at the front of the driver side head coolant is streaming out. It's hard to tell but it appears to be coming out at the very front of the head gasket... Is there anything else that could be leaking coolant in that area? Right under the air pump? Last year I had an intake gasket leak which I was able to replace... but it was a terrible job. How bad is it to replace the head gaskets? Any pointers or good writeups on the whole process? Should I replace the head bolts? Any tips on torqueing? Use antisieze? GM gaskets? How much would a dealer charge me to replace head gaskets?

Thanks!

 

Unless the head is cracked, it's from the intake manifold. Your '91 uses a special manifold gasket with retainers to fit into counterbores at the front and rear mounting bolts. Those bolts are also a bit longer than all the others so keep track of them when you R & R the manifold. As far as I know, the gasket set is Dealer only as they're unique to the '91 Vette. They were designed to keep the gaskets in place during manifold installation and to stop the numerous leaks that plaque all of the other years. Yours probably lasted longer than most. GM Part number is 12525814. Coolant restrictors go towards the rear. Before you remove the distributor, line it up with #1 and make a mark on the manifold to make it easier to get it re-installed correctly.

 

Make sure it's not streaming down from the intake under the front of the head. Headgaskets problems are real common for alluminum head L98's, though they usually leak internally. The gaskets for the 91 may be unique, but I've used the standard ones with no problems. Head bolts are recommended to be replaced, but again I've talked to rebuilders who say there is nothing wrong with re-using them. Supposedly they stretch when torqued, some engines require so much twisting after torque is reached (1/8-1/4 turn, can't think of the term, Northstars do, but 350's don't.

 

The term is 'Torque-to-Yield' (TTY).

A TTY bolt is first pre-loaded to an initial torque value, next it is
tightened to a specified torque value and lastly tightened an additional
specified number of degrees of rotation.

When under load, ductile materials have elastic, plastic and rupture
regions. Parts that are tensioned only to loads within the elastic
region may stretch under load, but they will return to the original
length when the load is removed and there will not be a reduction in
cross-section along the length of the part.

'Torque-to-Yield' intentionally tensions a fastener past the Yield Point
(the upper limit of the Elastic region). This permanently streches
the part and somewhere along the length, the cross-sectional size
narrows.

Engine rebuilders who reuse TTY fasteners are either doing so for
economic reasons or because they don't know any better. In either
case, they are gambling with the customer's money.

Part of the point of using TTY head bolts is to eliminate the need to
re-torque the bolts over time to compensate for gasket compression.
At best, a used TTY bolt won't be able to apply the same clamping
force and the gasket will leak sooner. At worst, the bolt will break
during installation or while in service, possibly causing other issues
besides the need to replace the bolt/repair the threaded hole.

Instead of using new 'Torque-to-Yield' bolts, traditional 'Torque'
bolts could be substituted. In this case, be sure to research and
follow any applicable guidelines regarding retorquing the head bolts
after several heat-cool cycles and then at regular intervals.

.

 

Tonight I'm going to remove the alternator and possibly the air pump... and pressurize the system to get a better look. But I'm 99% sure it is not the intake. It appears to be coming from well below the intake. My best hope is that it's the water pump gasket and it's spraying over to the head but I can't get a good look without removing the alt. If it's not the water pump gasket it's the head gasket... or oh my a cracked head?!? Can those be fixed? Is there a write up on eliminating the air pump?

 

Cracked heads are easily fixed if they are alluminum (Heli-arc them). I doubt you have a cracked head unless you've been getting it very hot. Make sure your throttle body isn't leaking, or that you don't have pin holes in any hoses, or loose connections.

 

Tips.

Be careful to keep the 'nut' on the case side of the cable end from
turning while loosening the cable retaining nut. Ideally, use the
correctly sized thin ignition wrench. Alternatively, use needle-nose
pliers. If the stud turns, a conductor inside the case can break - you
then need to disassemble the alternator to repair the broken conductor.

The cable to the alternator is electrically 'hot.' Disconnect the battery
ground cable before beginning to work.

My vote is that aluminum heads seldom crack. The much more common
problem on C4's is corrosion arising from electrolysis.

.

 

My local Chevrolet dealer says $2150 to replace head gaskets.

Is there a head gasket kit from GM that includes all gaskets and seals from the heads up? Anyone have a part number?

 

I don't know about a complete GM top end gasket set for the '91 L98.
Chris May at Superior might be able to help.

Fel-Pro #HS7733PT9 is a top end kit that includes gaskets for the
head, int/exh manifolds, runners, plenum, throttle body & ect.
However, it appears to be specified across several years - not just
for the '91. As SunCr mentioned, the '91 had features the earlier
engines didn't.

.

 

By now, most of your questions have been addressed. If you have determined that you need to change the head gaskets, you have experience with most of the job. Remember that intake manifold gasket job? That was most of a head gasket job. Once the intake is off, there are 6 exhaust manifold to head bolts and 17 head bolts per side to be removed. There may be some misc. connections, ground straps, etc, to deal with also. Once off, take the heads to a machine shop to be pressure checked and checked for flat and true. While waiting on the heads do a super thorough job of cleaning the deck surface of the block and the gasket surfaces of the intake. If this is the first time the heads have been off and the head bolts are NOT TTY, I would clean and reuse them. Torque, in steps, in the pattern shown in your FSM. No antisieze. Use a sealant, I like Permatex No. 2, on the threads of the head bolts.

You will probably will have other questions as you go, but this gives you a decent start. After all, you HAVE been here before. You have nothing to fear, but fear itself.

RACE ON!!!

 

I just did a head gasket replacement on my 96. If I can do it with the help of the forum members, anyone can if you have the patience. The FSM is also a must.

 

Okay, I must be living right... tonight I removed the alternator was able to pressurize the system and it appears to be a water pump gasket! With the alternator removed I can get to the bolts on the driverside. On the passenger side I have removed the plastic box that the air pump tube goes to. I started removing the AC compressor bracket and it looks like I will have to remove one of the fuel lines to get one of the bolts out. How much other stuff will I have to remove? I'm not complaining--this beats the head gasket to pieces... Can I eliminate the smog pump and this black plastic box?

 

Is there a write up anywhere on elimiating the air pump on a 91? I've been searching for an hour and cant find anything on a 1991???

 

The part # I posted for the '91 includes the Plenum and Runner gaskets. You don't need anything else unless you're yanking the EGR and thermostat.