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 Post subject: Cooling system problems
PostPosted: Tue Aug 07, 2018 10:54 am 
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Joined: Tue Aug 07, 2018 8:59 am
Posts: 2
Year and Trim: 1997 SE 3.8L
Hello everyone, I need some help with a problem I am having with my cooling system in my 1997 Bonneville SE w/a 3.8L non supercharged engine. The car sat for about 8 months because it took me that long to find somewhere to buy a set of pre-bent stainless steel brake lines, anyway, after installing the brake lines the car ran fine for about 2 months and then the problems began. First I had to replace the battery. Then the alternator quit. And now the cooling system trouble. 1st the temp gauge began fluctuating, high (220 deg.) and then back to about 180. Somehow that problem seemed to correct itself but started again in about 1 month. I have none of the tell tale signs of gasket problems, no water in oil, no oil in water, no visible leaks, and the car runs great but 2 times it built up pressure in the radiator bad enough to blow coolant out of the upper rad hose. I replaced the tstat and the cap, my temp holds steady at 195, no white smoke from the exhaust. Then the 2nd high pressure problem. Does anyone think if I replace the water pump, radiator, put aluminum hoses in the tensioner, and new upper and lower rad hoses this may solve this problem. Also, my cooling fans are working and I never had my temp over 220 deg, so I never overheated the engine. Thanks in advance for any help, Bill

PostPosted: Wed Aug 08, 2018 11:45 am 
Certified Bonneville Nut
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Joined: Wed May 13, 2009 10:45 pm
Posts: 5595
Location: CHICAGO
Year and Trim: 2006 STS-V, 2004 GTO, 2009 G8 GT
Probably just a flaky ECT sending unit or the stepper motor in the gauge if the car isn't actually physically overheating. 195* is right where it should be with a stock t-stat.

My inclination is the ECT sending unit being the culprit.


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
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2009 Chevrolet Impala SS: LS4 V8, Victory Red
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PostPosted: Wed Aug 08, 2018 12:20 pm 
Posts like a Northstar
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Joined: Sun Aug 22, 2010 11:11 pm
Posts: 1646
Location: Ontario, Canada
Year and Trim: 2000 Bonniville SSEi L67
hi, if the upper rad hose was original, it will swell with age and the spring clamp may cut into the hose - happened to my 2000.

yes, you cant really trust the gauge as above - if you get a scantool and pull the engine control/coolant temp, it pulls the reading from the PCM and will be accurate.

first rule out the funky gauge, then you can diagnose with confidence instead of blind assumptions.

poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

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