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1998 Deville
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76 Posts
Discussion Starter #1
Riddle me this, O Northstar wise people :confused::

Last week, my '98 Deville is running 217 consistently, up hill, down hill, highway and traffic. This week, she's running 222 (at least on the way to work) and peaking at 228 while waiting in traffic.

Now some background. I dropped the engine (don't know how to pull it out the top, but may have to learn...) and installed the Northstar Performance stud kit back in 2009. I've put 100K miles on her since then (she's up to 230K now) with some minor issues. I had to replace the water crossover gaskets, the surge tank, blower motor, heater core, and the radiator over the course of the last two years.

Consistently pulling 23-25 mpg combined. Instant mileage on the highway hits 30 mpg on level straightaways.

Did notice, last week, that after going down a mile long hill with the engine at idle (engine braking, if you will) when I applied the throttle to go up the other side, i got a puff of smoke out the tailpipes. Not positive, but believe it was white.

Do I perhaps have another head gasket issue? I haven't done a block test but may have to. How long should the studs last? Can I re-torque my head nuts?

Starts and runs fine first thing in the morning, even after having sat for the weekend, no stumbling or rough idle (at least that I can tell).

I'm debating replacing the thermostat (i haven't done that in the 110K miles i've owned the car). Fan belt seems alright, but can check again for slippage.

Any input would be appreciated.

Thanks,

Scott
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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For starters, 217 is NOT a constantly normal operating temperature. 190 - 205 is. Cooling fans go to SLOW at 224 with no HVAC A/C function set, so 217 is operating at the edge of the envelope.

What are you monitoring coolant temperature with ??

FWIW the thermostat (proper one) is set to begin opening at 188 and fully open at 206, so MOST Northstars run around all the time with the 'stat open about 75%.

Is the engine losing any coolant - frequent surge tanks checks and fill to proper level, cold ?
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,250 Posts
Riddle me this, O Northstar wise people :confused::

Last week, my '98 Deville is running 217 consistently, up hill, down hill, highway and traffic. This week, she's running 222 (at least on the way to work) and peaking at 228 while waiting in traffic.

Now some background. I dropped the engine (don't know how to pull it out the top, but may have to learn...) and installed the Northstar Performance stud kit back in 2009. I've put 100K miles on her since then (she's up to 230K now) with some minor issues. I had to replace the water crossover gaskets, the surge tank, blower motor, heater core, and the radiator over the course of the last two years.

Consistently pulling 23-25 mpg combined. Instant mileage on the highway hits 30 mpg on level straightaways.

Did notice, last week, that after going down a mile long hill with the engine at idle (engine braking, if you will) when I applied the throttle to go up the other side, i got a puff of smoke out the tailpipes. Not positive, but believe it was white.

Do I perhaps have another head gasket issue? I haven't done a block test but may have to. How long should the studs last? Can I re-torque my head nuts?

Starts and runs fine first thing in the morning, even after having sat for the weekend, no stumbling or rough idle (at least that I can tell).

I'm debating replacing the thermostat (i haven't done that in the 110K miles i've owned the car). Fan belt seems alright, but can check again for slippage.

Any input would be appreciated.

Thanks,

Scott
===================
I'm debating replacing the thermostat
(i haven't done that in the 110K miles i've owned the car).

I rarely blame the T-stat -
however -
because it is cheap and easy to do -
I'd say change it -

be sure to use a genuine ACDelco - or Stant -
Gates would also be OK in a pinch -

be sure to check the PURGE LINE for proper coolant flow -
 

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1998 Deville
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76 Posts
Discussion Starter #4
Submariner 409: I concur that 217 is not normal... but it was the "usual" temp showing up on the digital dash. Is there a better way to monitor engine temp? I've fought a number of coolant leaks since putting the engine back in, guess I didn't do as good a job as I thought... so I've become accustomed to periodically adding coolant, but it's actually settled down some since I replaced the radiator this past December.

Basscat: Agree the t-stat probably isn't the issue, but what the heck, they're relatively cheap, and I haven't changed mine yet... I'll check the purge line tonight when I get the car back in the garage.

Anybody hear of the Northstar Performance stud kit failing after 5+ years and >100K miles?
 

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White Diamond '03 DHS (with DTS floor shift)
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Studs don't fail. If anything fails, it will be the block. Have you read the "Root Cause" Sticky in the Northstar forum?

Hard to imaging it lasting 100K and failing again.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,250 Posts
should operating temperature ever get as high as 250 during the summer with the AC on?
\========================
no -
it is rare that the coolant temp runs hotter than 205 -

maybe briefly - if -
100+ ambient - AC on -
stuck in bumper-to-bumper traffic -
or going up a long/steep hill -
 

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1999 DeVille De Elegance
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106 Posts
ok, then its a high normal under those specific driving conditions. But temp should drop from there. Any danger to the engine if that temp is maintained for any period of time?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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If you weren't afraid of boilover you could change the thermostat and pressure cap and run the engine at 235 - 250 day in and day out - but the extra underhood heat would accelerate rubber and plastic deterioration, as well as absolutely dictate the need for an engine oil cooler. Oil is the only fluid that cools the internal reciprocating parts and valvetrain; it works best at 190 - 210 degrees, so it can then easily pass off collected heat to the block and head drains as well as the oil pan surfaces. Any chance of oil overheat and it oxidizes rapidly - thus the engine oil coolers in racing engines and HD vehicle towing packages.

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I concur that 217 is not normal... but it was the "usual" temp showing up on the digital dash. Is there a better way to monitor engine temp?
Your car uses the OBD-II diagnostic protocol. Look at a ScanGauge-II ( www.scangauge.com ) I monitor IAT, ECT, MAP, and IGN, but you can constantly monitor any 4 of 12 programmed "gauges" with the ability to program 4 more of your choice. No, we cannot monitor oil pressure from the existing on/off sending switch.

Deville main threads page - sticky post - Acronyms.
 

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2011 DTS Premium w/1SD | 1999 Deville Base (RIP @179K Miles)
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Just a heads up, I've had some problems with the scan gage OBD readers from eBay. When I plugged it in to my 1999 Deville, it triggered a lot of warning messages.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Hasn't happened to me in a dozen installs. They're OBD-II and CAN readers. Will NOT work pre-1996.

Better to buy directly from ScanGauge itself - eBay may just be the reason you have had problems. Several of us in The Kent Island Cruisers use the things in later model cars (the ones with phony gauges and idiot lights) and I occasionally plug one or two from behind the counter at Western Auto.

I run one in the STS and had two in two F-150s. Sold one truck, other is in the garage, ScanGauge in for 4 years. No troubles. Did you call ScanGauge ??? They're really good about questions and warranties.

EDIT: ---and follow the setup and install directions. When all else fails, read the instruction manual.

If you get antsy about a ScanGauge, look at UltraGauge.com.
 

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Fans not running correctly? Purge line clear? Belt tensioner giving its best tension?

Mine runs everywhere between 190-222 depending on the conditions. Although I agree that 228 is a bit on the high side. (The only time I see cars go above 224 is when it had some sort of trouble with their cooling systems.)
 

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1998 Deville
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Discussion Starter #13
Studs don't fail. If anything fails, it will be the block. Have you read the "Root Cause" Sticky in the Northstar forum?

Hard to imaging it lasting 100K and failing again.
I agree, but I have two concerns: 1, I did the studs myself, 2, see concern number 1 :yup:

I re-read the sticky on root cause failures and now believe I can rest easy that the head gasket shouldn't be failing again.

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If you weren't afraid of boilover you could change the thermostat and pressure cap and run the engine at 235 - 250 day in and day out - but the extra underhood heat would accelerate rubber and plastic deterioration, as well as absolutely dictate the need for an engine oil cooler. Oil is the only fluid that cools the internal reciprocating parts and valvetrain; it works best at 190 - 210 degrees, so it can then easily pass off collected heat to the block and head drains as well as the oil pan surfaces. Any chance of oil overheat and it oxidizes rapidly - thus the engine oil coolers in racing engines and HD vehicle towing packages.

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Your car uses the OBD-II diagnostic protocol. Look at a ScanGauge-II ( www.scangauge.com ) I monitor IAT, ECT, MAP, and IGN, but you can constantly monitor any 4 of 12 programmed "gauges" with the ability to program 4 more of your choice. No, we cannot monitor oil pressure from the existing on/off sending switch.

Deville main threads page - sticky post - Acronyms.
I'll look into additional gauges/sending units and see how accurate my digital dash is. I have noticed that when i first start the car, the coolant temperature shows 10-20 degrees higher than the outside temperature gauge. So, I really don't know what the temperature is doing...

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Fans not running correctly? Purge line clear? Belt tensioner giving its best tension?

Mine runs everywhere between 190-222 depending on the conditions. Although I agree that 228 is a bit on the high side. (The only time I see cars go above 224 is when it had some sort of trouble with their cooling systems.)
Fans are running, and appear to be running at a normal speed (at least they don't appear to be sluggish). If I was operating in a higher outside temperature area (I'm in south central Alaska where a high summer temperature is 70-75 degrees, and yes, the a/c works good :))

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Haven't had time to investigate further, but I believe I have a leak that only presents under pressure. Coming home the other day I got the "Check Coolant Level" notification on the dash for the first time in many months. When I looked under the car, I saw coolant dripping from the engine cradle... it appears the leak is coming from the passenger side, firewall side. Perhaps a heater hose or worse yet, one of the metal tubes that run along the back side of the engine that I don't believe can be replaced without dropping/pulling the engine...

I'm out of town for work for the next two and a half months so it will be a while until I can investigate and correct the issue.

I'll update when I can, and thanks to everybody's input to date.

Scott
 

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Inspect around the surge tank. It is known to get brittle over time and develop a crack. I had one that broke its purge line nipple.
 

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I have noticed that when i first start the car, the coolant temperature shows 10-20 degrees higher than the outside temperature gauge. So, I really don't know what the temperature is doing...

Change the ECT
. Nasty job, but do-able with hand tools and patience.

ECT sender from a NAPA, sender is down in the right side of the rear end of the block - to the right of and below the TB - in front of your gas pedal toes.
 

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