: Overheating --- Still!!!!!!!!

07-09-04, 10:33 AM
OK guys, I'm about ready to trade the damn thing in and never buy another Caddy!!! I've done everything you guys have said: 120psi within 15 degrees of TDC per cylinder for 5+ minutes, no leaks. Changed the thermostat, put the new coolant in, put the bars leak in, the vapor vent hose "pees", the hose from the surge tank to the thermostat housing is open, the tensioner is fine, the WP belt is brand new. WHAT THE HELL AM I MISSING????
I took it out this morning, ran fine with the gage a little over halfway for about 25 miles on regular roads. Decided to do the same test as before: passed a truck uphill in the passing lane, took it up to 100 mph, backed off and all hell broke loose. Gage climbed right up to the red marker, bells and whistles went off, coolant came out overflow and coated right side of car on the bottom.
Why only when I jump on it???? The only other option I have is the radiator, but I would think that it would act up regardless of engine load. I desparately need some answers, and I'm out of ideas. Could the mechanic been right - could the extra heat and load cause enough thermal expansion to open up a head gasket, but not show up on a cold engine under 120psi.

07-09-04, 06:11 PM
I hate to tell you this... but..... that is exactly what mine did. Not overheat but puke the coolant out whenever I jumped on it. If I didn't jump on it, it wouldn't puke the coolant out. The coolant came out of the coolant tank overflow tube. I put the the overflow tube out the edge of the hood and drive the car... something I wouldn't recommend by the way since the coolant blasts back all over the windshield :bonkers: not a pretty sight when you have look out of it... and when you turn the wipers on it just smears :suspect:. I have since replaced that motor with another that I have redone.. Headgaskets, timeserted... and a few other things. Now I beat the snot out of it every chance I get.

Just before I changed the engine and it was cold out I had a coolant between the front cylinder head and the block at before the engine got up to temperature. Now that I have the engine on an engine stand I checked the head bolts on the front head, the end ones, both ends were pulled or loose. I didn't check any further since I found the smoking gun as it were. I would be willing to bet I have a number of pulled head bolt threads on the back head as well which is no big deal since I was going to pull the heads and timesert this motor anyways.

My thought is that when you jump on it you are lifting the head enough to allow some combustion pressure from one of more cylinders to flow into one or more of the coolant passages over pressurizing the coolant system which in turn pukes the coolant out through the overflow tube.

Get under the car and see if you can see any weeping of coolant from between the cylinder head and block. I could see the bars leak on the side of the block. Also take a flash light and look in the valley by the power steering pump to see if it is full of oil or coolant. Mine had a mixture of both.

Good luck.

07-09-04, 10:05 PM
I thinks it your radiator. After the car gets hot, disconnect the battery and place your hand lightly on the radiator side facing the electric fans. If it is cool on the lower end and hot to the touch on the top, then it's definitely your radiator. We have had this prob with a couple of our cars.

07-09-04, 11:31 PM
changing the radiator will no help, head gaskets are your problem, do not waste more time and money and repair your head gaskets

07-10-04, 01:07 AM
If the head gaskets are sealing OK for the pressure test then I would think that they are OK. I have never seen a head gasket that is failed like some are theorizing that would still hold the air pressure when pressurizing the cylinders.

Since aluminum expands....the clamp load on the gasket is greater when the engine is hot...not less. So if it leaks hot then it should leak worse cold.

I would certainly investigate the radiator for now. If you have the time and patience remove it and take the tanks off for inspection. The tanks are plastic and are simply crimped to the rad core by tabes. Unbend the taps with pliers and the tank can be taken off to inspect the rad tubes for blockage. The tanks are then reinstalled by re-crimping the tabs by squeezing with pliers.

Just the opposite of what you are suppossing....a deficient radiator will definitely cause overheating when there is more load on the engine...not all the time.

The more load you put on the engine the more heat that is being rejected to the coolant so the more work the radiator must do. If the rad is compromised for some reason then it could still have adequate capacity for normal load operation but then when the load increases it would be insufficient.

07-11-04, 08:24 PM
OK Bbob, here's the latest. Took the rad out today, but didn't bother to take the tanks off. Figured if I did and the rad was plugged, I couldn't do anything about it anyhow. I'm taking it to a local rad shop to have it cleaned out - I remember an ex-girlfriend that had a 95 S-10 Blazer that had Dexcool, and the rad was so plugged from lack of maintenance that we just replaced it: then I replaced her!!

Anyhow, I have two questions: 1) is what Dloch said theoretically possible?? Even though the coeffecient of thermal expansion is different for the block/heads and the bolts, could a loose bolt allow the head to lift. Not having the bore/stroke/comp ratio, I can't calculate cylinder pressure but I would think it wouldn't be over 150 psi prior to ignition - if the head bolt were loose, the 120 psi in the chamber should lift the head. Basically, all we're doing is reversing the process: lock the piston and pressurize the cylinder, rather than the other way around. The only thing missing is the heat. Your thoughts??

2) I'm not familiar with the intricacies (?) of the Northstar water pump, and I never got a service manual yet. I know from reading the posts that the pump impeller screws on counter-clockwise: is the impeller then locked on the shaft? What I'm asking is that is it possible for the impeller shaft to spin inside the impeller under load. i.e. not pump fast enough??

By the way, who put that screw in the side of the plastic tank that holds the A/C lines to the condenser?? Can't get to the damn thing unless you take the computer out!!

As always, thanks for everyone's help. I want to keep this car, but I also want to trust it!!

07-11-04, 11:50 PM
Yes, the combustion pressure is much higher...around 1000 to 1400 PSI...but it is very very brief. The relatively constant 120 PSI airpressure in the cylinder will find any head gasket compression leak in my experience....

If bolts are loose or pulled then it would leak cold. Since the bolts are steel and expand less than the aluminum clamped in between in the block and head the tension in the bolt and/or load on the head gaskets increases with increasing engine temp. It doesn't go down. So, if the head gasket is leaking compression then it should leak even worse cold.

Some misunderstanding on the water pump. The cover of the water pump clocks into the water crossover casting in a counterclockwise manner....not the impeller onto the shaft. The impeller is welded onto the shaft. I have personally never seen an impeller come loose from the shaft and not turn. Just not a failure mode that is possible in my mind....but...I do keep an open mind. I would not suspect this as a problem, though. The impeller certainly does not screw onto the shaft as you imply. Unless there is some sort of aftermarket replacement pump that someone installed on your engine that has a "removeable" impeller I wouldn't suspect this as a failure mode.

The 4.1/4.5/4.9 engine was also this way...but there are aftermarket pumps for those engines that have pressed on impellers and I have heard of two of those falling off inside the water pump so the impeller wasn't turning with the shaft/pulley. Totally different water pump and geometry and such but the idea is the same.

07-12-04, 02:28 AM
We had a hard time diagnosing the first N* with bad head gakets, but I have an idea. It seems every one that needs gaskets needs timeserting. I would check the torque on the head bolts and see what happens.

The head bolts are torque to yield so there is no published torque spec. I would think it is more than 80 ft-lbs though. Try torqueing all the bolts to 80 and see how they act. If some move noticeably I'd suspect the bolts/gasket scenario.

You need a male allen socket. I think my set is from Lisle. I don't remember the size.