: It Happened,the dreaded overheat!

04-03-05, 11:35 PM
I thought I would be able to drive it('99 Deville) for a while even though I was losing coolant. I filled it every three days and all was fine. Until last night in the pouring rain on the Palisades Parkway, message came on that said engine overheat. Stuck, dead in the right hand lane. What happened to my limp home mode?? First it said idle engine, which I did. The temp went down slightly so I put her in gear and drove off. A few seconds later the overheat message came on and I shut it down. God I love GM cars!!

04-04-05, 12:57 PM

If you'd gone just a few more miles you'd have gotten the "disposal mode" warning on your dash! This is calculated to go off at the point where the trade-in value of your vehicle reaches the cost of having to pull the body away from the car to replace $50 worth of head gaskets...

Had I known the actual cost of keeping these cars running I'd have gone about the purchse much differently. Buy it at about 20K and trade it in just before 50K, or 2 years. My cost over time would have been less than the $$$ spent over the same time with an older car - my 14K used vehicle has cost me about 20K - I should've put the 6K in on the front end and gotten rid of the car at two years... my bad!

Hope springs eternal - my '79 deVille did the same thing to me... I'm waiting for my dash to show, "fooled you twice..."

04-04-05, 01:04 PM
You never got it hot enough to reach the limp home mode of operation. If you had just kept driving it would have gotten hotter and would have reverted to the limp home mode and it would/could have limped home.....

Stopping like you did certainly put the least overheat stress on the engine but, given it's past history, stopping was kind of pointless. I would have kept driving it until the limp home mode engaged and then kept on limping it to a safe/convenient place.

04-04-05, 04:21 PM
I must Say the Limp Home Mode got me off ther Hywy 2 times on my Headgasket problem.. Good design the limp home mode is.. BBob, it seems like the injectors go twice the duty cycle, err run very rich to help cool down the heads and engine, correct? I'm sure it also retards the timing, wont allow it to go over 2000 rpms or so. All these conditions help keep the motor as cool as possible...


04-04-05, 05:58 PM
I would be a little hesitant to "limp home" on a headgasket overheat. Isn't it possible for coolant to get into the oil and start wreaking havoc on the bearings?

Limp home did save me a tow when my wife's aurora's water pump belt broke. Its a nice feature, but I would not care to drive too far like that.

04-05-05, 11:53 AM
No, I'm not suggesting "driving" it anywhere of any distance in limp home but getting off the freeway or to a safe spot is what it is designed for.

The Northstar is not likely to put coolant into the oil even if a head gasket fails competely due to the design of the engine. There are no adjacent coolant/oil passages for crossleaks to occur.

The limp home mode does several things. It activates when it sees temperatures in the cylinder head that are indicative of a dry cooling system that is boiling and exceding the threshold of a "wetted" engine. The system shuts down 4 the injectors on 4 cylinders allowing them to cool themselves by pumping air while the other 4 motivate the car. Then the cycle alternates and the other 4 cylinders pump air and cool while the resting cylinders run the car. The power is SIGNIFICANTLY reduced so the car will barely maintain 55 MPH even in the best of circumstances...but...it beats walking and/or destroying the engine. The 4 cylinders that are running are ruch to help reduct temps as much as possible and the spark is retarded significantly to prevent detonation. The idle speed control/idle air control automatically bumps the idle speed way up to prevent stallling and the cooling fans are help on max high to push as much air thru the engine compartment as possible. The oil assumes much of the cooling duties in the limp home mode so the oil should be changed immediately after a limp home mode event.

04-05-05, 01:59 PM
Just my curiousity, is the N* very expensive to replace the head gasket? When will it tend to blow/how to I prevent such a thing from happening?

04-06-05, 11:29 AM
About the only thing you can do to help prevent it is change the coolant every 4-5 years (Dex-Cool) and 2-3 years (green). Other than that, if it's gonna go, it's gonna go. I've heard $3000-$4000 to change them as the drive train has to be dropped and the block Timeserted.

04-06-05, 01:54 PM

Good question, really... I've got 114K on my '96. The car is basically worth nothing at this point, even for trade-in value.

So, if your car is in perfect shape, no dents, interior still looks new, you may find the value built back into the car if you drive it another 100K after a set of new head gaskets. But, while you have the body pulled away from the engine to get to the $100 worth of head gaskets, you have a rare opportunity to get to ALL of the problematic parts.

I'd rebuild the A/C while you have access. $500, or so for parts. I'd replace the alternator at this point as well. Another $150, or so. Now'd be the time check the radiator and electric fans and replace as necessary. I'd do the blower motor at this point, as well, another $300, or so. Cabin filter could be done, too. You get the point...

The tranny, well, your choice, but at 100K it is probably due for some work. The cost of that depends on what is needed to bring it back to a like new condition.

I'm guessing I'd be spending around 2K on parts alone if I did ALL the work. If it is done for you, 6 to 7K. But, the drivetrain is ready for another 100K.

My car has too many nagging electrical problems to make this all worth while - the jobs mentioned above would take quite awhile if you did them in your garage... and then when you factor in your time to do all of these things, well, there's the real cost...

I made a very basic mistake when I bought my car. I should've put the 6K on the front end and driven the car for two years and traded back at about 50K. The best part of 100K on these cars is the first 50, not the last 50!

My bad, I won't make this error again!

Much sucess!

04-08-05, 02:41 AM
Just my curiousity, is the N* very expensive to replace the head gasket? When will it tend to blow/how to I prevent such a thing from happening?

A dealership will charge about $4,000 to repair both headgaskets.

The parts and usually replaced items, including the Timesert kit, will cost about $900. Labor is the big expense for this job.

See the attached PDF for a look at the costs I put out for my 93' STS, yours would be very similar.


04-08-05, 08:23 AM
I was quoted $2200, to do both headgaskets from a reputable Caddy dealership.

04-08-05, 08:32 AM
I was quoted $2200, to do both headgaskets from a reputable Caddy dealership.

$2,200 is a very good price, if it includes Timeserting ALL twenty head bolt holes and the other common worn out items, including the usual oil pan seepage.

At that price I may have elected to have mine done by a dealer, as it was no one even came close to that price; so I did both of my cars myself.


04-08-05, 09:54 AM
I had mine done on a 95' Eldo for $4,000 with new time-serts at a reputable Caddy dealership. 3500 miles later a rear bolt pulled out. And I paid $7000 for a new Northstar. Get a warranty in writing. I think I am headed to small claims court.

04-08-05, 09:03 PM
The $2200 was only a quote, but I called an independent shop and they quoted me $2300 for the same job. The book time on headgasket repair is 20 hours, so I figure 20 hours at $100 dollars an hour and $200 dollars in parts could be close.

They may not have included the timserting in the quote? Timeserting may bring the total closer to $3000.

I found a cheaper option, a salvage yard engine for $1500 and a local wrench to install for $300 - we will see how that goes

Multi Caddi
04-11-05, 11:20 AM
Over Heat ? but not headgasket ??
Calling BBobynski + Other experts Can you assist ...99 STS 67K miles runs fine around town, temp guage is at "12oclock" normal but run it down the motorway at 80+ and the temperature suddenly goes up round to the red slow down to 60 and it cools down back to normal doesnt happen every time some times a motorway trip will be fine.

When it did boil I pulled of the motorway stopped the engine and very slowly released the expansion cap at first not much happened then there was gurgling then hot water found its way to the expansion tank and bubbled up, i tightend the capslightly to prevent water loss but allowed steam to escape, after retightening the cap went back on the motorway, engine temp perfect, this currentl happens about every 2/3 journeys

Starts and runs good, no oil in water, its clean , Oil is perfect, water pump an dthermostat replaced,radiator removed, endcaps removed passages cleaned, fans all operating, at the correctspeeds relay all ok !

The exp cap is often leaking steam after a run, I supect that exhaust pressure is getting into the water jacket and over pressuring the system at high speed!
Any Ideas ??
I see the egr valve is located in the water crospipe have we ever had leaks in this area
Thanks for all inputs

04-11-05, 12:05 PM
Some possibilities that come to mind:
The hollow bolt above the water pump needs to be clear so that the water pump can vent air back to the surge tank.

Remove the 3/8" hose and use the largest drill bit that will twist thru the hollow bolt BY HAND, to make sure it is not blocked.

The hose that leads back to the surge tank must also be clear. With the surge tank cap off and a couple of rags placed over the opening, blow thru the small hose with compressed air, from where it connects at hollow bolt.

Verify that the water pump belt is in good condition and that the tensioner can use its full travel to tension the belt. Sometime the tensioner sticks and will not apply full pressure; and then the belt will slip.

The water pump tensioner is relaxed with a 1/4" drive extension placed in the square hole. After slipping off the belt verify that the tensioner can freely travel its full range.

Sometimes engine detailers get carried away and get various protectants get on the belts and it makes them slippery. It might be worth removing the water pump belt, and washing it in hot water with dishwashing soap to be sure. Also wash both pulleys to make sure they are clean and oil free.

Top off the coolant to about 2" below the surge tank opening.