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'01 SLS w/ 64,000 mi. randomly gets hot then cooler then o-heats

3K views 32 replies 10 participants last post by  97EldoCoupe 
#1 · (Edited)
just got a 0'1 Seville with 64,000 miles. The car is second owner car, well serviced. I checked the car out, let it idle about 20 mins., and the temp was fine. Took it for a good ride and still ok. Of coarse soon as I got it and got on the rode home, the gauge would rise and fall randomly. It didn't seem to matter if I was on a grade, level or down hill. At a traffic signal, going 25 or 70 mph. Really random. Tested relays, checked fuses.
Temp. sensor? Thermostat? I kind of know the cars history and it had been maintained regularly.
also it's not popping codes.
Thanks,
Scott
 
#3 ·
Re: '01 SLS w/ 64,000 mi. randomly gets hot then cooler then o-heats, then cools, hot

sorry, I forgot. The fans aren't coming on right. I thought they'd come on when hot, but one side did come on (weak) when it cooled down. now it's not coming on again

----------

Thanks, I'll check them tomorrow!
 
#5 · (Edited)
Here's your fan circuit. 3 relays and fuses in the underhood fuse box - locations on the sticker in the box top. Those 3 relays are TIGHT - and the pins sometimes oxidize. Hope it's a relay or a fuse - the actual fan/motor/wiring replacement is not fun.

Pictures and diagrams of the cooling system and parts in my albums - click my username, open the profile. Left column - 2 albums, 6 pages of stuff for your car.

The 12 o'clock mark on your temp gauge is highly damped - it covers (within a needles' width) a range from 190 to 215. God forbid a Cadillac owner should ever see a "gauge" actually move ! Read the sticky posts in Engines; Northstar for background on your cooling system, fan, and temp gauge operation. The thermostat starts at 188 and is fully open at 206 - and they are most reliable.

Both fans run at the same time - relay-set to series for low speed, parallel for high speed. MC's temp setpoints are correct.
 
#7 ·
So I pulled the purge line and fitting. It didn't seem 100% blocked. I also noticed the hose and clamp @ the thermostat housing have a lot of corrosion around it. Would bad thermostat cause fluctuation in temp? Where is the coolant temp sensor? Should I test it? Should I jump the fans to check operation?
Thanks for everyone's help! Go 9ers!!! Oops! maybe I should wait til the cars on the road before I say that! Don't want to alienate anyone!!!
 
#19 ·
You're an exception - most CF members go paranoid if the gauge even MOVES during a pit stop at KFC.

Engine condition, ambient temperature, coolant condition, HVAC (A/C compressor) settings, plus a skrillion other variables dictate coolant temp at any given instant.

I occasionally run my STS to over 140 mph. During a forced (transmission in 1) deceleration from that speed, the injectors turn off and coolant temp drops by as much as 10 degrees before touching the gas pedal at ~35 mph - believe it or not, a LOT of air flows over and around that engine at speeds above ~35 mph - that's why cooling fans are not needed at speed.



EDIT: If you would like to watch your engine and systems functions in real time and value, take a look at a ScanGauge-II - either online or at many parts stores. I monitor MAP, IAT, ECT, and IGN. (Acronyms ^^^)
 
#21 ·
Posted many, many times - You drop the stick to 1 and do WOT acceleration. The 4T80E will upshift at redline/load rpm and will NOT let you break anything. Downshifts occur when load and lower gear rpm will damage nothing...... all with the stick in 1.

Try it. That gear number says "This is my preferred gear" and the transmission will stay there until it shifts at the correct load/rpm to protect itself.

WOT - Wide Open Throttle - absolute max acceleration possible. That pedal on the floor disables all emissions controls and allows the engine to do what it was designed to do: RUN.

Even though your car (VIN Y ?) is speed limited to 112 mph (VIN 9 is 130), you can easily exceed 90 in 2nd before a 2 - 3 upshift WOT.

Disclaimer:
Unless you are intimately familiar with your car and its characteristics and unless the car is in 100% excellent mechanical condition, DO NOT attempt high speed/high acceleration operation. One bad tire is disaster.
 
#24 ·
Then you have not done a "WOT". Go up to the Cadillac Technical Archive and read up on "Occasional full throttle operation is good ..........". Learn that procedure - a simple "punch it in the merge lane" is nowhere near a dedicated WOT run.
 
#23 · (Edited)
OK. I have never just left it in 1st.
I do do wot on a regular basis though.

that is only the first - "fun" half - of the WOT PROCEDURE -
that is recommended for the Northstar motor -

the deceleration portion of the WOT PROCEDURE is the most important part -

it sucks "extra" oil up onto the cylinder walls -
and that "extra" oil helps clean the piston rings -
 
#26 ·
SO... I do have water flowing to the purge tank from the purge line. The water gets warm going through the line.
A couple of things I should mention. I've only had the car a couple of days. I never really paid much attention to Cadillacs before. I traded a dirt bike for this one because my truck took a crap and I needed a daily driver.
The car was unbelievably clean in and out with low mileage. Now that I've got it, even though I only drove it 20 mins. before it started crapping out, I'm sold and want to keep it. The rides unbelievable, and the overall qualities amazing! My hope is it's something I can fix and save the car.
The other thing is that when I pulled the thermostat, it was covered in rust and the rubber was shredded. This leads me to believe there's been no coolant in the passages for some time.
So what is the way to flush the system? (which side is the petcock on too?)
How do I burp the air out? (is there a bleeder valve?)
Thanks in advance!
Scott
 
#27 ·
Get yourself a block test kit. Borrow one from AutoZone and just pay for the test fluid. That test will rule out or condemn the HG's as the problem. It is possible that it has a HG failure and the previous owner wanted to unload it.

The other thing is that when I pulled the thermostat, it was covered in rust
Are you sure it was rust and not the muddy rust colored sealant tab residue.

This leads me to believe there's been no coolant in the passages for some time.
Remember, the water jacket is aluminum and thus does not rust.

So what is the way to flush the system? (which side is the petcock on too?)
Just keep adding water until it runs clear. The drain plug (#10) is on the drivers side. Keep in mind, it's not the same petcock you grew up with.




How do I burp the air out? (is there a bleeder valve?)
Just run the engine as you fill it. Then rev it to about 3K and hold it for 30 seconds or so 2 or 3 times then cap it up before it gets warm and overflows. It is self purging so any remaining air will be purge when you drive it. Just check the level after the next 2-3 drives until it stabilizes.
 
#28 ·
So the verdict is in, blown head gasket. Damn. I really like the car and don't want to get rid of it. Anyone know who I could take it to in the Sacramento/ San Francisco bay area that wont rip me off? Since Ive got all of the money I had to buy a car into it, I can't afford to get rid of it. I could really use your help!
Scott
 
#31 ·
Sacramento native here. Theres a shop in the Roseville area thats pretty reputable, cant remember the name though. I wanna say its GM repair center of Roseville

424 clinton ave
Roseville CA 95678
916-773-3390.


They know how to install studs too
 
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#32 ·
I have used GM Repair Center for my 2001STS. For me my block cracked on an otherwise great running engine. They did an engine swap putting in a complete engine from Northstar Performance. I purchased the engine from Jake, it was one of the first (maybe the first) he built from the new blocks he had purchased from GM. This was about 2 years ago engine has about 100k on it now and runs great with no leaks...Thanks Jake great engine.

Back to GM repair center in Roseville. At the time they were doing several engines using Jake's studs. Did great work for me at a reasonable price and I have had no problem since with their work.

Worth a check out if you are in Sacramento area.

Richard
 
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