'86 Vette

I'm in the process of replacing intake manifold gaskets on my '86 Vette to fix the leak I've been chasing for 15 years and 10K miles. This car is the reason I have Big-Block Buicks:laugh: . And every time I work on this Chevy "powered" sports car I remember all those reasons people give about the lack of quality control at GM in the '80's.:rant:

It makes me wonder how a GN or GNX was assembled!

 

Fel Pro has some gaskets that are "supposed" to keep those problem leaks from occuring over and over. They have a steel core wrapped in rubber. Can't say from personal experience, but I sure did sell a lot of them. Don't recall any comebacks either.

 

The coolant leak is now fixed after a lot of careful assembly work so as to avoid breaking many more wiring harness connectors. HOWEVER, now I have a bigger problem than before.

In the past the coolant temp has always been higher than I should was acceptable. The hope was that by fixing leak I could keep the coolant inside the engine and thereby lower the coolant temps. They have always been in the 210 to 230 range with the cooling fan coming in at 230.

Now with the leak fixed the temps are SCARY HOT ( 301 peak) I think the radiator cap releaves about 260. I have been careful to not modify anything away from factory specification. It's all GM until this point except the Fel Pro intake gasket set.

My first thought is that the thermostat is stuck close. My second is that the intake gaskets are not correct for the engine and there is a closed/ restricted coolant passage that needs to be open.

Is there a diagram somewhere that I can look at to see what the cololant flow should be on this engine? I have read a description of it on a Corvette forum but I would really like to see a diagram.

 

How does it perform? Logy? Make sure your timing is right. Or, the leaks may have drizzled something into the exhaust and fried your converter. Try disconnecting the head pipe at the converter if the timing is right. Just checking vacuum drop at RPMs isn't always a good check for a clogged converter.

 

Air pocket in the cooling system from filling it up ?? o No:

 

I have been thinking about the possible differences in the early-1986 and late-1986 intake gaskets. The part numbers are different and maybe the passages and block-off plates are in different locations.

So I will be checking the part numbers to verify tomorrow. I also had a chance to speak with a Corvette specialty shop and see what they think. The engine specialist hasn't done one in a while but remembers that the primary difference was the location of the block-off plates and the size of the restriction in the ones that are not totally blocked. He also verified what I have learned about the coolant flow diagram I have drawn up after reading the two paragraph description in a Corvette forum. We also discussed the air pocket issue and dtermines that this is relatively unlikely in my situation.

Back to the verify and possible disassembly again.

 

I got part number MS93316. That is one of two choices for a '86 Vette with cast iron heads. This is apparently is not a common part and there is no detailed information about it from what I can find. The other option is the MS93035-1. That fits the '85 'Vette as well as some other years of Camaro, Trans Am, etc. with a TPI 305 or 350. The late '86 to '91 'Vette use MS93318-1.

I have the MS93035-1 on order and will know more tomorrow.

 

So I've replaced the intake gasket again. The new part number is different in that it DOES NOT have restrictions on any of the coolant passages. Now that I have the coolant leak from the intake manifold the system hold enough pressure to discover that the water pump is leaking badly from the lower weap hole. Now onto a getting the water pump rebuilt.

 

The water pump works great after being rebuilt. The change in intake gaskets has solved the coolant temperature problem. I haven't seen more than 215 degrees yet.

However, I am now chasing a miss. It could be firing order/ timing issue, or vacuum leak or the possibility of a head gasket or cracked cylinder head. Given theat the temps went to 300 may have caused the latter according to the Corvette experts I have talked to. And it would make sense.:af: Compression test is up next.

 

Compression test complete; #1 125 #2 130 #3 130 #4 130 #5 130 #6 130 #7 130 #8 135. I was suspecting a very low cylinder or two. However, the plugs show a large amount of wear and are all over the board with coloration etc.; from way too lean to way too rich. Installed new correct AC plugs and no change in idle quality.

Thoughts. symptoms are a surging idle and roughness that acts like a vacuum leak from somewhere.o No: :rant:

 

It's probably a "vacuum leak from somewhere." I bet that engine has a lot of vacuum hoses, some of which are actually rigid plastic. It's REAL easy to miss hooking up one of the connections, or knocking a connection loose, or have a crack in one of the rigid lines. The end result is not only a vacuum leak but also a computer or emissions component which isn't operating the way it should.

Of course, you mentioned the possibility of firing order; you're on your own to check that.