Hi !
Ive had several Cadillacs pre northstar, and been wonderful, i picked this 1998 Cadillac Seville SLS, knowing about the possible head gaskets issues, but could not say no, its in amazing , mint condition, super clean, it actually runs smooth, after 20 minutes or so of driving, coolant read hot on display and gauge, and displayed engine overheating, i also lost heat, so i changed the thermostat, heat seemed okay, back on the road, it did the same thing, my mechanic ran the compression test, no leaks, compression ok, also no white smoke from exhaust, no antifreeze in the oil, no leaks, tried driving it again last nite and again gauge went up to hot, display showed engine coolant hot and then eventually displayed showed engine hot..it was usually after 20 minutes, ohh and after i parked and idled i had no heat again.. i dont want to jump the gun and assume its the head gasket, 98k miles and considering the antifreeze level is the same and the compression test came up alright... What else should i do or try. Its a shame this car is so nice, comfortable and in pristine condition.. hate to lose it.. please help !

 

i have a similar problem on a 99 sls,,,i'm going through the coolant system,troubleshooting it,,,in my case this is my mother's car that we bought last year and it had a small coolant leak,,,but she wouldn't give up the car so i could troubleshoot it. long story short,her water pump finally went out,,,,so i replaced it,,,the thermostat looked good, so i held off on that,,i also had to replace the water pump pulley,belt and tensioner,because the pump had frozen,,,melted the plastic pulley,and broke the tensioner...we still have a problem,,,the vehicle runs hot but i won't let it overheat,,,i now know that the cooling fans don't come on,,these are controlled by relays actuated by the powertrain control module/engine control module,,,i'm now trying to determine if i need to replace the computer and if so how i can program it,,,,i already changed all the relays and the engine temperature sensor,,,,,,,


get a manual for your car dawg,,,this will help you troubleshoot your ride

on my vehicle here is a list of all the components involved

powertrain control module
engine temp sensor
thermostat
cooling fan relays
cooling fan fuses
water pump
engine coolant
radiator
reservoir tank
reservoir tank cap

any of these being defective will cause the car to overheat


i will try to remember to update your thread when i get my car fixed,,but you can hit my email if you need to,,,if anyone that reads this thread has any insight it would be appreciated

 

Hey thanks so much for the reply greatly appreciated, ya i have the list, u forgot the last possibility of the head gasket, in my case non of the symptoms of a head gasket issue are showing, its not leaking fluid or getting in the oil, no white smoke, etc.. Although the antifreeze reservoir smells like exhaust after a few minutes.
So a new thermostat, system flush, cleaned out hoses, fans work, radiator's good, heater core good, next may be looking into the water pump, temp sensor or faulty sending unit. It seems like many people jump the gun to the gasket issues...
or may just take a loss selling for 1500, OEM cadi chrome rims are probably worth that.. Cheers ! Thanks again, its enthusiast like you that make this such a great site and motivation to keep on cadilakin,

 

frank how does it run,,,mine doesn't over heat per sey,,,but i live 5 min. from my job and it gets to operating temp in that time,,,i know the cooling fans don't come on and the tank boils over,,,so i ride the bus to keep from driving to avoid blowing the engine,,,i just came from this site *

 

i will get what i need from these cats if i have too,,,later i will get an engine from them cause i want to,,,i will keep you posted as to what i find out about my ride,,,,tomorrow i take it to my mechanic so he can troubleshoot the things i have researched and suspect

 

Ya it runs and shifts great, smooth cadi ride, plus the power of a v8, the gauge will start to go into the red after 20 minutes or so of driving or idling then display will read "engine hot / overheating" and computer starts to turn off ac, then it will display "turn off engine" if u keep driving and will then struggle to drive.. and when i check coolant its boiling, once it cools down the radiator fluid in the tank is still in the same place, so its not loosing coolant.. strange !

 

Frank,,,i won't drive mine that long,to keep from blowing the head gaskets,,,so you have answered a question of mine about the limp mode,,,it sounds like your car goes into limp mode,,,my mechanic has my ride right now so i will get back after i talk to him

 

ok, Thank You, It might be sold today as is, dont want to deal with again, i may get back into the older cadis, easy to work on

 

Try burping the system