I have a 90 c4 that has about 109xxx on the clock. hasn't given me much trouble 'till now. The car used a gallon of coolant and started missing on a cylinder. I added coolant and drove it home , not far. Got it home, added more coolant and started to figure out the miss fire. # 7 cyl wasn't firing. changed out the spark plug, still not firing, but now smoking bad. I pulled the #7 plug and found coolant on it. OK this is bad,. So I figured the intake was prob the culprit. #7 cyl had good compression. So I pulled the center section of the intake. There is some small amounts of coolant in the main ,center section of the intake, and in a few runners. I pulled the entire intake off. The gaskets and intake manifold seem ok. Is there some way the coolant is getting into the upper section of the intake , and therefore getting into a few runners ? I don't want to pull the heads off if I don't have to.

 

Is there any way the coolant that warms the throttle body could leak into the upper intake ?

 

If it had a bad head gasket , would there be coolant in the upper intake ?

 

any help would be appreciated thanks

 

No.

 

You probably have bad intake manifold gaskets (where they mate to the heads).

It does sound like your head gasket is blown at #7. Pull out the spark plugs and compare them. Usually a blown head gasket will "steam clean" the plug and the end will be very clean instead of carboned up.

You might also get interesting results from pulling all the plugs and cranking the engine. In my case water came out of the spark plug hole for #7.

 

hello hello rather b driving.

yes u have a leaking head gasket 7. usually on the block side of 7.

i am about to get my heads decked at the shop. im just a but further into the journey.

its possible you coolant getting tinto the intake as well.

many pics on my thread on this if you want to see what a "blown" head gasket looks like here u go. The 1990 and 1985 will be a little bit different, example you have aluminum heads whereas I have iron heads but for both, its number 7.

https://www.corvetteforum.com/forums/c4-tech-performance/3735399-seeping-intake-bolts-1985-affect-idle.html

 

from what I've read on this forum, aluminum head L98's are hard on head gaskets, especially at the #7 and #8 cylinders. some speculate it has something to do with the coolant restrictors in the intake manifold gaskets. it doesn't seem to be as much of a problem on it's iron head brothers. I recently replaced the intake gaskets on my 90, and went with the open port design of the iron heads (used 1985 manifold gaskets). I also kept the steam tube configuration. it's been about a year now, and even with the hot florida summers, my coolant temps seem normal. I can say that I don't fully understand the coolant flow through aluminum head L98's, and the effects of using and not using restrictors. if the OP is adding that much coolant, it sure sounds like a head gaskets.

 

I'd recommend a cooling system pressure test. If you're losing that much coolant - the pressure test should point you in the right direction.

If you do the pressure test at a point (engine rotation point) where the #7 cylinder intake valve is closed - there should be no way that coolant gets into the combustion chamber unless the head gasket has failed or a cylinder head has cracked.

You could also try a leakdown test - it's done at TDC of the compression stroke, and if you see bubbles in the coolant or hear noise in the radiator - you're going to be pulling the cylinder head or heads.

IMHO - a LOT of people seem to think long life coolant is lifetime coolant. It seems that a number of owners - particularly people who don't plan to keep a car past 5 - 6 years - don't bother to change coolant. Modern coolant contains a lot of additives (an additive package if you will), some of those additives are designed to protect against corrosion, and while not super accurate - you can look at those additives as sacrificial, so if you don't replace coolant you will see a loss in corrosion protection. It seems that the head gaskets are one of the areas that are impacted when this happens. Not saying the OP was lax on maintenance, but there does seem to be some kind of increased probability of a head gasket failure with a lack of coolant changing.

Oh - one other thing - coolant is poison to Oxygen sensors. If you are burning that much coolant - you have hurt the oxygen sensors on that bank - you might get a little more life out of them - but plan on changing them real soon.

 

for a leakdown,,,, all u need to do is get a spark plug thread to air hose hose ( some 50-ish$ compression testors also can be used as this, u dont need to be at tdc. just put 80lbs ish psi into the cyl 8 and u will bear normal hissing + probably hear bubbles in the overflow reservoir. need to have coolant in the resrvoir for this to work. by far the fastest easiest wat to pinpoint headgasket failure.

my compression was great but still i burned coolant in 7, burned oil in all ofthem through a blown head intake gasket. i did fail the coolant pressure test as well. but it doesnt tell u much other than what u know already.

 

Ok i was in denial about the head gskts. I have faced the fact that the heads have to come off. I was removing various parts off the engine and I decided to pull the engine and go with a rebuild. It is a stock 90 with a larger injector in it by PO. I have heard u can go with 10-1 compression and a pretty fat cam and not affect the computer. I have not pulled the engine yet ,, but will do shortly. Can anyone give me a good combo of a budget build on this 90 c-4 ? I was thinking of 10-1 pistons , how far will stock heads go as far as camshaft lift ? i am planning on using the stock heads (if they are not cracked) stock crank n rods, stock intake.... thanks

 

Before you start buying parts you had better find out who can do a tune for your car (computer) that is close to you. Or if no one is close, you had better be prepared to go with a mail order chip and be able to do data logging to feed information to the chip maker.

Anytime you change the cam that is enough different from stock you will need a new chip.

You might consider a short block 383 from someone like Summit or Jeg's as a base for your build. If your going with new heads, cam etc....better figure about $4000 - $5000.
\

 

The rebuild will be more than the car is worth. Sad but true.

Vic

 

A larger injector as in 1 or all? If all, do you have the specs?

Why do you think you can screw with getting a fat cam and not affect the thing enough that you need a retune? Tom400CFI, I think mad that sort of thing work by crafting everything around the ECM. IOW, figure out how much more air and increase the fuel pressure to match. IDK if you can do that easily but I would think, in the end, it might be less aggravating to simply get it tuned.

So what exactly is your resistance to getting a tune?

 

It always will be when you are dealing with an older car. So if you are not prepared to pay, don't play. Everyone wants fast, reliable and cheap. Why not toss in some fries and a few hookers and blow? Not happening in this life.

 

what, no fires, hookers and... damn - and I really like fries . I've been following another thread by the OP on this subject - on the fast, reliable, and cheap thing. in reality, one can only achieve two out of three....

 

"seem okay" and being okay are two different things; one, if you have "good compression" the head gasket is probably okay; if you have a bad head gasket you can expect lower (or no compression) compared to other cylinders, and even if the leak is minimal and compression hasn't been affected (yet) the "products of combustion" will work there way past the head gasket and (typically) you can expect an over pressured cooling system with the radiator cap lifting;

if you need further analysis, a simple chemical test for the presence of combustion gases in the coolant will tell all.

More likely, and the presence of coolant in the runners could be a clue, is a leak from the coolant passage (at 15 psi positive pressure) past the intake gasket into the intake manifold (at 15 inches hg vacumn).

I have misdiagnosed a leaking intake manifold gasket for a leaking head gasket.

I'd try the $50 solution first (replace the intake manifold gasket) before I tried the $500 solution (pull heads, do valve job, replace the head gaskets) or the $5,000 solution (replace engine).

 

One would think but Viking Trader had gone through compression testing and it was fine but the head gasket was apparently toast.