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Discussion Starter #1
Hi everybody, new guy here.

My neighbor has a caddy with a northstar engine. He was complaining that it would overheat and the computer would tell him to shut it down.

I took off the radiator cap and set the display to temperature and watched it slowly go up to 212 at which point we shut it down.

No steam in the overflow. I noticed the top pipe was hot and the bottom was cold. The overflow was FULL to the brim when I opened it and stayed full throughout
the test. Around the middle of the upper pipe in front of the radiator it was hot but not as hot as I would expect it to be.

The car is not consuming any coolant. not exhaust bubbles in the overflow and the overflow stayed cold.

Any ideas would be greatly appreciated.

Thanks
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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212 isn't overheating, not even close.

The fans don't even go to low speed operation until 224. High speed operation is at 236.

What year/model is the car? Under what conditions is it telling him to turn off the engine? Idle/low speed? Highway driving? Acceleration?

The coolant tank is not a reservoir, it's a pressurized part of the system with a small amount of flow, called a surge tank. Proper fill level is to the FULL COLD line in the tank, about where the two tank halves meet.
 

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No 212 is not overheating. But the drop the thermostat make didn't happen. He was concerned we would burn the engine so when I saw it reach 212 without lowering and kept on going up we shut it down.

He gets an engine shut down message driving 3-4 miles mostly in the city sometimes getting on the highway for 1 or 2 miles. It's a sedan deville. hes not home right now but the car says it's a 32V northstar. Yeah I know. That's all I have at the moment.

The surge tank must be overfilled because it's too the brim.
 

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White Diamond '03 DHS (with DTS floor shift)
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Find out what year it is.
If the surge tank is full, it will puke out the excess as soon as it get to operating temperature (212).
Check to see if the purge line is clear and flows coolant.
If so, and it still overheats, borrow a block test kit from AutoZone (just pay for the test fluid). Run the test and report back with the findings.
https://www.youtube.com/watch?v=vgkMC-5Mtz8&feature=player_detailpage
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Here's a quickie - if his temp gauge covers a sweep of 135 degrees instead of this 180 degrees (9 to 3 o'clock) the temp lines are the same. Read the notes on the picture, and study the 3 sticky posts on this forum main page - cooling system, fans, gauges.

A little knowledge goes a long way in this case.
 

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Discussion Starter #6
Thx guys.

Sumariner. This caddies has a digital output.

Its a 96.

what hoses need to be flushed? Im not too familliar with this model.

I think we have a blockage. As you said if the tank is full it will overflow and ot doesn't. This morning the car was cold and the tank was full. I took the cap off and let it idle until 212 and not a drop spilled.

In my experience the coolant expands a dif your expansion tank is full it spills.

Thanks again to everyone for their help...
 

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Oh yeah. The purge line is clear. I stuck my finger in the expansion tank and coolant dripped out of the hose
 

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The tank won't split, the excess coolant will be expelled through the overflow.

You want to find the purge line. It's the small hose that runs between the upper part of the surge tank, and the hollow bolt/nipple near the water pump. With the engine cool, remove the surge tank cap, disconnect the purge line, and stick it into the open tank. Start the engine. You should see a slow, steady stream of coolant from the hose. The line itself is usually not what's clogged. The hollow bolt nipple is usually the problem. It can be "fodder out" using a wire hanger or nail.

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ggenovez said:
Oh yeah. The purge line is clear. I stuck my finger in the expansion tank and coolant dripped out of the hose
Sounds like you're talking about the overflow hose. That hose is near the cap neck, and isn't connected to anything on the other end.
 

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From your description of the finger dip, the surge tank (it is NOT an expansion tank) is grossly overfilled. Proper level - cold - is half full; at the tank midseam.

The overflow hose sticks out the side of the filler neck. The purge line - pressurized constant bleed - runs from the water crossover hollow bolt/nipple to the top side of the surge tank.

Please read the first paragraph of Post 5 again. You need to understand this cooling system.
 

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Discussion Starter #11
Thanks Ranger.

Ok. Got that. Disconnected that line and the other end to it. Even though there is Green coolant, red cam out the other end. That's the thermostat housing right?

I took the end from the tank and blew on it and coolant came out the the thermostat housing side. Is it safe to assume that hose is clear? anything else to do while i'm at it?

Here is a video I found of the expansion tank/surge tank I'm referring to

https://www.youtube.com/watch?feature=player_detailpage&v=0sFFe4TnYks#t=175

Where is the blockage usually located?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The blockage most often occurs inside the hollow bolt/nipple at the water crossover, next to the water pump cover/thermostat housing. Use a straightened coat hanger and "rod out" the bolt/nipple thoroughly. About 2 1/2" deep.

The hollow bolt/nipple is in this diagram - it's a constant bleed that removes air and gases from the coolant. (The EGR and throttlebody are different for the 1996 - this is a 2000+ setup.)

Look at Post 10 again. The picture. See the FULL COLD legend molded into the surge tank top ? There's also an arrow there - follow it across the tank top and down the side - it points to the tank midseam.
 

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Discussion Starter #14
Thanks guys,

Ok, I disconnected the surge tank hose. No flow. I disconnected the purge line hollow bolt also no flow. I used a paper clip and pushed it in.

no resistance and still no flow.

I tried brining the car up to temp hoping the paper clip had done anything. nada. Still no flow to the surge tank.

Upper hose got hot. Lower stayed cool
 

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For cleaning the purge line bolt/nipple a paper clip is like using a .22 to shoot an elephant. Either get crazy with a straightened coat hanger to a depth of 2.5 inches or so or use a proper sized twist drill, hand-spun.

If the purge system is operating as designed it WILL pump coolant to the surge tank at all times.

I didn't look back through the thread, but have you verified that the water pump drive system is intact and working properly ?
 

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To inspect the water pump drive system you remove the steel safety shroud and push-pull-wiggle the belt, tensioner, and water pump pulley. Shredded belt, rattley tensioner pulley, water pump noise - all not good. The large drive pulley is tightly - tightly - pressed onto the left bank intake cam extension. If some other pump drive part fails and ruins that pulley you have a miserable replacement job ahead............ special removal and install tools, for starters.

Did you go back and thoroughly clean out the purge nipple ? Coolant should steadily run out of that line at idle.

Last resort - replace the water pump. One occasionally sheds the impeller shroud and that's the end of any pumping ability. Special removal/install socket and a few special procedures to follow. Cadillac Tech Tips.
 
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