So Ive just bought a 91 Seville. I've been driving it around a bit with no issues (short drive to work, and about a 40 mile trip on the freeway). Today I'm sitting in line (idling for about 5 minutes) to get environmental inspection, and she starts spewing steam. After I get out of the line into the lot I track where the steams coming from. Drivers side of the radiator, not the top rubber hose but a metal fitting right underneath it that leads to the oil filter. I checked the overflow canister and my coolant wasn't boiling or overflowing. I also notice that my fan isn't turning on. Put the computer into diagnostic, and all i get is the ISC error (which I already knew about)

Im wondering also what the operating temp of the coolant is supposed to be, and at what temp are the fans supposed to come on.

Im waiting for my Chiltons to come in the mail, and Im hoping to get my hands on the FSM. Until then, does anyone have any feedback on what the issue might be? Is it all because my fan isnt turning on?

And sorry if this has been discussed before, I did a quick search and couldn't find anything like my prob.

So Ive just bought a 91 Seville. I've been driving it around a bit with no issues (short drive to work, and about a 40 mile trip on the freeway). Today I'm sitting in line (idling for about 5 minutes) to get environmental inspection, and she starts spewing steam. After I get out of the line into the lot I track where the steams coming from. Drivers side of the radiator, not the top rubber hose but a metal fitting right underneath it that leads to the oil filter. I checked the overflow canister and my coolant wasn't boiling or overflowing. I also notice that my fan isn't turning on. Put the computer into diagnostic, and all i get is the ISC error (which I already knew about)

Im wondering also what the operating temp of the coolant is supposed to be, and at what temp are the fans supposed to come on.

Im waiting for my Chiltons to come in the mail, and Im hoping to get my hands on the FSM. Until then, does anyone have any feedback on what the issue might be? Is it all because my fan isnt turning on?

And sorry if this has been discussed before, I did a quick search and couldn't find anything like my prob.

The operating temp is 195F. The engine can get much hotter when you stop. The fans turn on at 226F, bring it to 212 and stop. Depressing Eng Data on the climate control will show RPM, temp, battery voltage etc. Your problem does not seem to be serious. Probably all you need ias a new o-ring where the oil cooler is connected to the end tank. BTW, the end tanks are plastic and may develop cracks.

ISC motor is some $75 and is easy to replace. Does it make loud ratcheting noise when you shut down the engine?

Thanks for the info. Sounds like my fan isn't turning on when it should.

What is that plastic end-tank for? Oil cooler of sorts?

And for the ISC, the guy I bought it from told me that the one on there is shot (it does make the loud ratcheting noise, and I get the error code for it). He included a spare, he just didn't get around to switching it since he wasn't driving it anymore.

Thanks for the info. Sounds like my fan isn't turning on when it should.

What is that plastic end-tank for? Oil cooler of sorts?

And for the ISC, the guy I bought it from told me that the one on there is shot (it does make the loud ratcheting noise, and I get the error code for it). He included a spare, he just didn't get around to switching it since he wasn't driving it anymore.

The both end tanks of the radiator are plastic. One contains oil cooler and the other ATF cooler. Make sure the coolant does not get into the oil. If it happens change the oil ASAP and address radiator issue. Looks like the easiest way is replacing the radiator with an aftermarket one for some $150, or getting OEM end tanks from gmpartsdirest.com or dealer for some $70 and replace them if you are handy.

So the driver's side end tank of the radiator, with a metal hose coming out of the top and bottom, should be holding oil. The fact that coolant was most definately spewing from the top end of that metal hose, cannot be a good thing.

So first off is to replace the end tank/radiator. Then check/replace oil. (Will changing the oil suffice or should I do a flush?) And, of course, find out why the fan isn't coming on.

Are the aftermarket radiator products of a sturdier build? Or is OEM the way to go for longevity?

So the driver's side end tank of the radiator, with a metal hose coming out of the top and bottom, should be holding oil. The fact that coolant was most definately spewing from the top end of that metal hose, cannot be a good thing.

So first off is to replace the end tank/radiator. Then check/replace oil. (Will changing the oil suffice or should I do a flush?) And, of course, find out why the fan isn't coming on.

Are the aftermarket radiator products of a sturdier build? Or is OEM the way to go for longevity?

Change oil only if you see signes of coolant. You do not need to flush, just get rid of old oil and filter. BTW, the best oil for your engine is Rotella or Delvac 15W-40 . These oils provide greater antiwear protection for high mileadge engines. I personally replaced the end tanks and kept the original core of the radiator. The job is not that difficult, but took some four hours. The end tanks come with all the necessary gaskets.

Several people had good luck with aftermarket radiators. I believe they are all aluminum.

I couldn't find any part that fit that description on gmpartsdirect.

Does this sound like the part i need? (radiator outlet tank) (http://domestic.eautopartstore.com/item.wws?sku=52463746&mfr=ACDELCO%20US&weight=30&cookieID=1T519EXYQ1T519FVG9&clientid=domestic.eautopartstore)

Or, could i block off the inlet and outlet on that tank, and replace with an oil cooler thats seperate? if possible, i would prefer to seperate the oil cooler from the radiator, just to make sure that this doesnt come up again.

I couldn't find any part that fit that description on gmpartsdirect.

Does this sound like the part i need? (radiator outlet tank) (http://domestic.eautopartstore.com/item.wws?sku=52463746&mfr=ACDELCO%20US&weight=30&cookieID=1T519EXYQ1T519FVG9&clientid=domestic.eautopartstore)

Or, could i block off the inlet and outlet on that tank, and replace with an oil cooler thats seperate? if possible, i would prefer to seperate the oil cooler from the radiator, just to make sure that this doesnt come up again.

How would cooler work if you separate it from radiator???? Do not reinvent radiator! LOL I would replace the both inlet and outllet radiator tanks while you are at it. They are notorious for cracks.

Just any aftermarket oil cooler, working as its own lil radiator, such as this maybe (http://store.summitracing.com/partdetail.asp?autofilter=1&part=DER%2D15502B&N=%2D128262+115&autoview=sku)

If I have the chance, I'd replace the transmission side with a seperate unit as well. Just having those failure-prone plastic units jammed onto the side of the radiator doesn't sit easily with me.

Finding fittings would probably be the hardest part. Mounting these things is never all that difficult.

Side note, just purchased the FSM. Can't wait to dig into that. Chiltons might be in my mailbox right now.

New end tanks would probably serve for another 15 years, but it is of course up to you... Good luck!
BTW, looks like you are low on coolant. Check the level (when cold) in the radiator not in the surge tank.

While I would like to go with the seperate coolers, Ill probably just go with the ease of the side tanks.

Lets just hope I don't forget to find out whats wrong with my fan too....

Ok. I've finally gotten around to taking the caddy to the shop. Went ahead and replaced the whole radiator (end tank was very cracked, couldnt find end tanks for sale seperate) After that was replaced they found that the coolant wasn't moving (still overheated), so I had the water pump replaced.

So now, when Im driving around it'll stay between that 212 and 226. At stops though, it just climbs and climbs. It got to 235 just now before the light turned green. After we got moving again the temp was quick to drop back down to normal levels.

At the shop, the mechanic was talking about the fan having three speeds (true?) and that the fan wouldn't get up to the top speed. Could this be why its getting hot at stops? Something wrong with the fan, motor or relay perhaps?

Ok. I've finally gotten around to taking the caddy to the shop. Went ahead and replaced the whole radiator (end tank was very cracked, couldnt find end tanks for sale seperate) After that was replaced they found that the coolant wasn't moving (still overheated), so I had the water pump replaced.

So now, when Im driving around it'll stay between that 212 and 226. At stops though, it just climbs and climbs. It got to 235 just now before the light turned green. After we got moving again the temp was quick to drop back down to normal levels.

At the shop, the mechanic was talking about the fan having three speeds (true?) and that the fan wouldn't get up to the top speed. Could this be why its getting hot at stops? Something wrong with the fan, motor or relay perhaps?
Your temps are still higher than usual. Th efans should not allow the temp climb over 226. They will bring it down to some 212. There are two speeds, not three. Hav eyou replaced the thermostat? I would.

The thermostat was replaced after the radiator and before the water pump.

I'm thinking it HAS to be something fishy going on with the fan.

I don't think you understand that the end tanks on the radiator are designed to hold coolant. Inside the tank is another little heat exchanger that transfers heat from the oil routed to it to the coolant inside the tank so that it can be eliminated in the radiator. The radiator end tanks hold coolant just like on all radiators. The only difference in the one you are looking at has an oil cooler inside of the tank for the engine oil. Most all automatic transmission cars have a cooler like this in the end tank....just like yours does on the other end.

The fact that coolant is leaking indicates that the end tank has likely cracked and needs to be replaced. Eliminating the oil cooler will NOT address this issue in the least. There will always be coolant in the end tank and it will always leak until the end tank is replaced. You can remove the end tank by uncrimping the tangs that hold the tank in place (after you remove the radiator from the car which is the hardest part) and reinstall a new one. The oil cooler itself can be transferred to the new end tank as it is likely fine.


Trying to reroute coolers and lines and add coolers and such is a nightmare waiting to happen. It is FAR FAR easier to just replace your radiator or the radiator end tank than to try and recreate the oil cooler external to the radiator.....and even if you did it is not going to solve the coolant leaking problem.

You do not even know if you have a cooling or overheating problem. All you know is that the end tank leaks. It can leak and steam and cause problems even if the engine coolant temperature is fine. Since the radiator is pressurized it can easily go above the boiling point and then appear to "boil" if a leak develops. The temp is probably fine if you just address the leak. It will have to be addressed anyway so get with it before panicing.

I don't think you understand that the end tanks on the radiator are designed to hold coolant. Inside the tank is another little heat exchanger that transfers heat from the oil routed to it to the coolant inside the tank so that it can be eliminated in the radiator. The radiator end tanks hold coolant just like on all radiators. The only difference in the one you are looking at has an oil cooler inside of the tank for the engine oil. Most all automatic transmission cars have a cooler like this in the end tank....just like yours does on the other end.

The fact that coolant is leaking indicates that the end tank has likely cracked and needs to be replaced. Eliminating the oil cooler will NOT address this issue in the least. There will always be coolant in the end tank and it will always leak until the end tank is replaced. You can remove the end tank by uncrimping the tangs that hold the tank in place (after you remove the radiator from the car which is the hardest part) and reinstall a new one. The oil cooler itself can be transferred to the new end tank as it is likely fine.


Trying to reroute coolers and lines and add coolers and such is a nightmare waiting to happen. It is FAR FAR easier to just replace your radiator or the radiator end tank than to try and recreate the oil cooler external to the radiator.....and even if you did it is not going to solve the coolant leaking problem.

You do not even know if you have a cooling or overheating problem. All you know is that the end tank leaks. It can leak and steam and cause problems even if the engine coolant temperature is fine. Since the radiator is pressurized it can easily go above the boiling point and then appear to "boil" if a leak develops. The temp is probably fine if you just address the leak. It will have to be addressed anyway so get with it before panicing.

Maybe you didn't read page 2? I realized that adding a different cooler is kinda silly, so I did just replace the radiator (and water pump and thermostat)

The problem now is that my temp still climbs at stops, but drops quickly once i get going.

I was just reading in my FSM about fan tests i can do (and will do soon)

It also comes to mind, with my ISC being bad, and having a high idle, could that cause a rise in temps at stops? What should the idle be? I think I read in the FSM 550, that sounds low to me (but what do I know?)