Jcu1287

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Jun 23, 2019
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1990 L98 C4 Coupe
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I drove the old 90 coupe to work this morning and said low coolant so after adding almost a gallon I finished my morning commute and then when I left this afternoon to head to the other office it said low coolant again after adding a total of 1.5 gallons since the day before. Also it sputters a little at idle when at a light. The temperature went up to red line almost 260 and when finally parked it was bubbling in the radiator as I could hear it. The oil on the dipstick looks slightly milky and is over full. No white smoke or visible leaks tho. Is this my head gasket? Has anyone else had this problem before? Thanks in advance for any advice or help. My 1st C4 so it's a learning curve for me but I will not get rid of this car.
 
Ya... milky oil is a pretty clear sign. Best get the engine properly diagnosed before it grenades and becomes hugely expensive to repair or has to be totally replaced.
If the coolant isn’t dripping out anywhere... it’s being consumed. Almost 100% some of its going out your exhaust pipes too. Sounds like you may have a warped head from high temps possibly.
Not the end of the world but it’s going to be a pretty big repair. I would pull the entire engine apart as milky oil doesn’t lube bearings and shells worth a damn.

Let us know what you end up doing.
 
Number 0ne cause is a failed head gasket, but also a bad intake manifold gasket can cause the problem too. Another possibility if the engine has a oil cooler that cracked then it is possible for oil to get into the coolant or vise versa. Since oil pressure is greater than coolant pressure when engine is running then oil will go into the water, but if engine is off and there is pressure in the water then coolant will flow into the oil. The sign of bubbles in the reservior and top rad hose hard as a rock when running is a sign of compression getting into the water. You mentioned a miss in the engine, that could be water leaking into a cyl, usually #7 on those engines from what I remember reading. I would not run it anymore as is. If sat long enough and water is leaking into a cyl, it is possible that later when you hit the starter the engine will lock up as water does not compress and you could bend a rod or crack the block. If you removed all the spark plugs and winged the motor over it might spit water out the bad cylinder(s).
 
Number 0ne cause is a failed head gasket, but also a bad intake manifold gasket can cause the problem too. Another possibility if the engine has a oil cooler that cracked then it is possible for oil to get into the coolant or vise versa. Since oil pressure is greater than coolant pressure when engine is running then oil will go into the water, but if engine is off and there is pressure in the water then coolant will flow into the oil. The sign of bubbles in the reservior and top rad hose hard as a rock when running is a sign of compression getting into the water. You mentioned a miss in the engine, that could be water leaking into a cyl, usually #7 on those engines from what I remember reading. I would not run it anymore as is. If sat long enough and water is leaking into a cyl, it is possible that later when you hit the starter the engine will lock up as water does not compress and you could bend a rod or crack the block. If you removed all the spark plugs and winged the motor over it might spit water out the bad cylinder(s).

For the amount of coolant he has added and it’s not in his oil pan and flooding the sump, it’s pretty clear it’s being burned up.
Yes must be a leak that diminishes as the engine cools as I agree with that much loss of coolant it would have hydraulically locked a cylinder or 2 if it was leaking substantially with the engine cold.

You definitely added some good points Michael.
 
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Thanks man I will be taking her into the shop this weekend or should I saw towing. I won't risk hurting her any more. I knew it would need some love and $$ like any sexy woman.

You’re totally right about the $$ comment 😂

Where are you taking you car for this work. Got a good corvette friendly shop near you?

Very helpful for other guys in your area to know.
 
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I am hoping it's just a head gasket and not anything more severe. Seems like a gasket from my experience working on cars. Just wanted some input from the Vette community. Any other suggestions would be appreciated. I do have a guy here in Vegas I trust and like I'm taking it to.
 
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Thanks man I will be taking her into the shop this weekend or should I saw towing. I won't risk hurting her any more. I knew it would need some love and $$ like any sexy woman.
Even so called good gaskets may not be up to snuff. This is from an intake that had the bolts torqued in the proper sequence and to proper torque specs with a torque wrench. No telling where the water would go with this mess.
Disintegrating Gasket-1.JPG
 
Even so called good gaskets may not be up to snuff. This is from an intake that had the bolts torqued in the proper sequence and to proper torque specs with a torque wrench. No telling where the water would go with this mess.View attachment 29145
Yeah it seems like this is the most possible issue. I'm going to let the shop diagnose it and throw on some extra goodies that I've been wanting to get done anyway. I'll let you know what the outcome is.
 
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I had the same issue this spring.Actually...last fall. I had a 180 thermostat in it, and I had JUST done the burp and had good steady coolant levels afterwards for a few weeks.
I parked it after seeing it go over 200 and the red line lit up.
I blocked it up for the winter, got my Mustang on the road, and came back to it this spring.
After checking all fluid levels and such after one stores a vehicle, and I see no coolant.... Gone..... WHT...I add some and hear it gurgle. It never did that before. I start it up and add more coolant, looking for a blown hose maybe.
Nothing. No milkshake either, and look at the tail pipe and shes got white smoke. Dam. Mosquito fogger.
Off to Canada Engines for a tear down and sure enough, blown head gasket.
.040 oversize and stage 2 cam and she is a new sound to her and nice little valve overlap giving it a nice brup brup at idle. Gas mileage went out the window tho, lol. 14mpg in the city now from 17mpg.
Now is the time if you plan on doing a supercharge or turbo application later down the road, and get some forged pistons. Hypers will shatter .
 
I had the same issue this spring.Actually...last fall. I had a 180 thermostat in it, and I had JUST done the burp and had good steady coolant levels afterwards for a few weeks.
I parked it after seeing it go over 200 and the red line lit up.
I blocked it up for the winter, got my Mustang on the road, and came back to it this spring.
After checking all fluid levels and such after one stores a vehicle, and I see no coolant.... Gone..... WHT...I add some and hear it gurgle. It never did that before. I start it up and add more coolant, looking for a blown hose maybe.
Nothing. No milkshake either, and look at the tail pipe and shes got white smoke. Dam. Mosquito fogger.
Off to Canada Engines for a tear down and sure enough, blown head gasket.
.040 oversize and stage 2 cam and she is a new sound to her and nice little valve overlap giving it a nice brup brup at idle. Gas mileage went out the window tho, lol. 14mpg in the city now from 17mpg.
Now is the time if you plan on doing a supercharge or turbo application later down the road, and get some forged pistons. Hypers will shatter .
Yeah that sounds about the same issue. I know once it's done I'll have better peice of mind driving it again. Gotta love them old C4s
 
Been through it. Blown head gasket, not much white smoke but bubbling in a/f pressure tank. Also leaking externally.
Needed heads machined, oil completely flushed to ensure no residue in block and.... all good except it still got hot running through town. New rad fixed that and its been fine ever since. Cost? not cheap, but its only money spent on your corvette.
Good Luck
 
Been through it. Blown head gasket, not much white smoke but bubbling in a/f pressure tank. Also leaking externally.
Needed heads machined, oil completely flushed to ensure no residue in block and.... all good except it still got hot running through town. New rad fixed that and its been fine ever since. Cost? not cheap, but its only money spent on your corvette.
Good Luck
Mine set me back 6K all in.
 
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Friends it's only the intake as I found out this morning. So less money and getting transmission service and nuew fuel pump cuz the fuel gage just stays at full. Anyone else have fuel their fuel level reading stop working? Just wondering if it's a fuel pump issue or something electric.

Good news on the coolant leak fix... Well. Compared to what it could have been that it... As for your fuel pump, it sounds more like the float is stuck or the sending unit is awry. I'm assuming the gauge needle moves when you turn the key on (thus not the gauge). I'd be tempted to try a bottle or two of Techron additive before I got too carried away. JMO
 
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Good news on the coolant leak fix... Well. Compared to what it could have been that it... As for your fuel pump, it sounds more like the float is stuck or the sending unit is awry. I'm assuming the gauge needle moves when you turn the key on (thus not the gauge). I'd be tempted to try a bottle or two of Techron additive before I got too carried away. JMO
It's a digital gauge so no movement just says full all the time.
 
hmmmm.... Certainly not a C4 expert here but my C7 is a digital and it moves up to the fuel level when I start my car. Maybe someone with a C4 could chime in here...
 
I concur with Eric, Jcu. Be it either a digital meter, or analog, the sending unit in the tank is what sends the voltage on a sort of a reostat pickup. Think if it as a flat snail. The higher the resistance I think it is, on the narrow end of the semi circle, would read as empty say. That would be the level indicator. If that pickup on the fuel pump arm is jammed or shorted out at the other end, the resistance value will be giving you a full tank reading. I had an old cop car that did the same thing. Paranoid it was always running out of gas. lol
 
I concur with Eric, Jcu. Be it either a digital meter, or analog, the sending unit in the tank is what sends the voltage on a sort of a reostat pickup. Think if it as a flat snail. The higher the resistance I think it is, on the narrow end of the semi circle, would read as empty say. That would be the level indicator. If that pickup on the fuel pump arm is jammed or shorted out at the other end, the resistance value will be giving you a full tank reading. I had an old cop car that did the same thing. Paranoid it was always running out of gas. lol
OK yeah that makes sense I was just wondering if it was the gauge itself but I'm having a new pump n sending unit installed anyway just to be safe. I plan to replace normal wear n tear items and possibly do some Hp additions. Possible supercharged or single turbo in the next 5 years which I know requires a lot and $$$$ but it's a sentimental car so I'm not seller her.
 
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