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I'm new here but saw an old post from Deadsled about overheating on the 500 motor.I have a 74 500 in a Corvair truck.It has been running for 9 years with no problems. Overheated really bad about month ago. This post is way beyond cooling systems 101 and have tried everything. I have tried 3 new waterpumps and there is no water flow at all. Some times I get a large discharge from the rapid heat input in the block, which is a input not output when I rev the engine. I was convinced that the pump was dead headed but I sent pressurized water through the wp holes in block, block drain holes and head water holes, both directions. With thermostat out and motor running there is NO water flow,no bubbles just steam after about 5 minutes. New head gaskets, good compression and no change in timming, Just no flow, even at 3000rpm
 

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New head gaskets??
When was this as compared to the first overheating episode?
Something has to be blocking the flow between the block and the heads, and for it to completely block this flow it has to be doing it on both sides of the engine at once.
So either the new head gaskets are made incorrectly, causing no flow, or there was/is a LOT of sealant used, to the point of blocking the openings in the gasket.
Maybe describe the exact sequence of events surrounding the first overheating episode, and we can get a better idea of what’s going on.
Also it’s not clearly stated whether the ‘garden hose’ to the block inlet actually flowed water out of the head.......

Bjc789
 

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New head gaskets??
When was this as compared to the first overheating episode?
Something has to be blocking the flow between the block and the heads, and for it to completely block this flow it has to be doing it on both sides of the engine at once.
So either the new head gaskets are made incorrectly, causing no flow, or there was/is a LOT of sealant used, to the point of blocking the openings in the gasket.
Maybe describe the exact sequence of events surrounding the first overheating episode, and we can get a better idea of what’s going on.
Also it’s not clearly stated whether the ‘garden hose’ to the block inlet actually flowed water out of the head.......

Bjc789
Motor overheated and had nothing but steam in the motor. Radiator water was still there. Pulled stat and it was bad. Refilled system and quickly heated up. Compression good but a lot of pressure in system. Left bank about 50-75 degrees hotter. Pulled heads, left head warped. New had gaskets matched old. Filled block around cylinders with CLR and installed, Good compression, same outcome. I tried 2 new water pumps (checked) and with stat housing off and stat out, no water flow, even at 3k rpm. Removed both block drains with no flow from left side. Applied air press to left drain and really black sludge came out of left water pump inlet, just rusty water on right. made adapter plates to replace wp and used a pressure washer to blast through block Same amount of clear water came out head and stat housing as was put in. Air in left drain again, still black water came out, rusty on right. Seems ther is flow but not in lower cylinder section. Filled system up and started, front of motor was 300, rear 175, still no flow, but got about 12 in. high stream from rapid heat inlet under stat. That seems to indicate backward flow. This is driving me nuts and seems to defi physics. I am on SS so can't afford vat and rebuild. 5 other fulltime mechanics are stumped. Thanks for the help
 

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Did you figure out what may have caused the original overheating episode?

If there is still gunk coming out when flushing with water or air I would keep flushing until the water is clear.

Steam pockets will block water flow, exacerbating the overheating issue. Steam pockets could be formed by a cracked cylinder wall or a head gasket not sealing properly. Or blocked head gasket coolant holes.

You said the head(s) were warped. Did you resurface them? Use different ones?

Did you check the rad independently for flow? Perhaps a shwack of goop left the block and plugged the rad tubes. Try reverse flushing the rad.

If it is overheating ‘fast’ as compared to gradually it is likely that combustion pressure and temperature is getting into the coolant passage.

I would pull that engine apart and clean/inspect it closely. It may not be serviceable without a rebuild, assuming the block isn’t cracked.
 

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My first thought was possible incorrect head gaskets are missing coolant holes but you checked that already.

Perhaps a good flush would help? This one is cheap and effective. Sounds like you have a decent pile of sludge buildup.


Are the heater lines open or closed? The water pumps you installed are not reverse flow pumps by chance? Just brainstorming with you here.....

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Discussion Starter #7
My first thought was possible incorrect head gaskets are missing coolant holes but you checked that already.

Perhaps a good flush would help? This one is cheap and effective. Sounds like you have a decent pile of sludge buildup.


Are the heater lines open or closed? The water pumps you installed are not reverse flow pumps by chance? Just brainstorming with you here.....

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Water passages are clear. Pump is sealed (no air), no stat and water all the way up to top of block.Two kinds of pumps, still no circulation, no pressure.Overheats in about 4 mins..
 

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Just thinking.... if i were you. Get that Prestone "T" I linked above and flush the ever living snot out of it with a garden hose. Especially since you already have the thermostat out. Heck throw some Cascade dishwashing detergent in it here and there (because it does not foam up). Do this once a day for a week between drives if possible.

Small Block GM LT1s have this problem because they are reverse flow cooling systems and get air bubbles easily.......maybe your baby just needs a good burp too.

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Just thinking.... if i were you. Get that Prestone "T" I linked above and flush the ever living snot out of it with a garden hose. Especially since you already have the thermostat out. Heck throw some Cascade dishwashing detergent in it here and there (because it does not foam up). Do this once a day for a week between drives if possible.

Small Block GM LT1s have this problem because they are reverse flow cooling systems and get air bubbles easily.......maybe your baby just needs a good burp too.

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Ive done CLR, Termo Cure, Cascade.None of this matters if he water wont flow. Thanks Ugly Mother
 

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"No thermostat" is half the problem. The Cadillac thermostat is "special", it covers/uncovers the coolant bypass port.

There's no "air" in the system if the thermostat is out. Any air would rise to the top, transfer to the radiator, and be seen as a "low coolant level".
 

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Discussion Starter #11
"No thermostat" is half the problem. The Cadillac thermostat is "special", it covers/uncovers the coolant bypass port.

There's no "air" in the system if the thermostat is out. Any air would rise to the top, transfer to the radiator, and be seen as a "low coolant level".
I think you missed something here.This setup is in a truck with no heater,adapted Chevy stat housing. The stat is out to monitor water flow. This setup has been running for 9 years. Average temp was 190, huge cooling system. I can run the motor with the top of stat housing off to monitor.The pump does not pull or push water in or out. No blockage found, just sits, at any rpm. 5 other engine builders/mechanics have never witnessed anything like this. I am not arguing, just defies physics.
572571
IMG_20190602_132043.jpg
 

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I think you missed something here.This setup is in a truck with no heater,adapted Chevy stat housing. The stat is out to monitor water flow. This setup has been running for 9 years. Average temp was 190, huge cooling system. I can run the motor with the top of stat housing off to monitor.The pump does not pull or push water in or out. No blockage found, just sits, at any rpm. 5 other engine builders/mechanics have never witnessed anything like this. I am not arguing, just defies physics.
View attachment 572571 View attachment 572571
the air I was speaking of will prevent a waterpump from pumping, that is not the problem. I believe there is something internal with a water passage but no water in oil. Im to the point of trying another motor.
 

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Of course not. you cant find this In a Chilton manual and guessing, ive tried. I even hooked the bottom hose up to the top hose, filled to top, compleating a loop, still no flow.
Sorry Scherkey im not getting short with you but I have already stated all this.Water from a hose flows both directions. All 3 new pumps will not circulate any. Tried 2 different brands, pulley not slipping.
 

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You dont suppose that a radiator hose is collapsing internally somehow? How new are they?

......brainstorming......

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You dont suppose that a radiator hose is collapsing internally somehow? How new are they?

......brainstorming......

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Good when this all started but replaced again. I stated before when I ran the bottom wp hose to the top stat hose to make a loop. I can leave the top of stat housing off to see whats going on and water was shooting out the quick heat input (backward flow).That has not happened again, water wont move at all now
 

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You said the head(s) were warped. Did you resurface them? Use different ones?

Did you check the rad independently for flow? Perhaps a shwack of goop left the block and plugged the rad tubes. Try reverse flushing the rad.
Since you didn’t answer the above questions I’m asking again.

A warped head cannot seal properly and combustion pressure will get into coolant area.

A cracked cylinder wall will do the same thing.

Physics isn’t being defied. It is manifesting in the symptoms shown. The trick is to comprehend it.

Distance diagnostics is difficult at best. However the simplest things are usually the fault.

Thus: major overheat = damaged head/block.

I think you SHOULD use a different engine. Two benefits. You will have a working vehicle again. You can tear down the first engine and find out the actual problem.

Bjc789
 

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Any luck on this?

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Sorry, been out of the loop. The only motors I can find around here are "ran when parked" and don't need another project. I took the heads off,again, poured water in the block around cylinders and it ran back out waterpump inlet, so no blockage. Thing just wont pump the other way
 
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