I just got my '98 Bonneville SSE back from the shop.

Last week it stumbled while driving, I drove one more block and parked at my destination. Six hours later it would not crank over, hydrolocked.

The shop diagnosed manifold/gasket failure, installed a new after-marker UIM kit and new lower gaskets, also a set of plugs and new thermostat/gasket. They flushed the oil twice, and flushed out the coolant, and refilled with "gold" type coolant. They said the car seemed to run fine at that point, smooth running, no unusual noises, etc. They say they road-tested the car. I drove the car about 5 miles the day I got it back.

Yesterday I took the car out again. I drove it about 2 miles, and when I pulled into the parking lot I noticed a slight wisp of steam from under the hood. It was after dark, but from what I could see with a flashlight, the steam seemed to be coming from the engine side of the radiator fins. No other noticeable symptoms. Gauges looked fine. I turned off the engine, and let the car sit for about an hour.

When I came back to the car, I checked again with a flashlight. No visible sign of leaks. The oil level, if anything, was a bit high. I couldn't clearly see the oil color since I was working with a flashlight. I forgot to check the coolant reservoir (doh!).

At this point, it started fine, and I drove it back home (another 2 miles or so). Idling in the carport, I saw more wisps of steam from the engine side of the radiator. At this point the coolant reservoir was empty, but warm to the touch. The exhaust may have been excessive and white, but perhaps that'* a judgement call, as the outdoor temp was mid-30'* and the car was barely warmed up. Again the gauges read OK.

Any thoughts as to what'* going on here? Something else related, or unrelated, to the manifold job? What would be some intelligent things to test? Compression? Cooling pressure test? Explain in detail if you like.

THANKS!

Check your oil for signs of water after about a 5-minute drive. It shouldn't look milky at all. The low coolant could be from simply filling an air pocket that wasn't burped, but it could be mixing with the oil or being burned off in the exhaust, both bad things. Does the exhaust smell like coolant? After the miles you drove, any moisture left from the work should be gone.

So refill your reservior to the cold full mark, and keep a very sharp eye on it and your oil the next time you drive, then be prepared to take it back to them immediately. Also check the coolant elbow on the passenger end of the LIM for leaks.

Because your coolant overflow tank was empty, it would be a good idea to open the radiator cap when the engine is cold and make sure the coolant level is all the way to the top of the radiator filler neck. If not, fill it with the same kind of coolant mixed 50-50 with water. Replace the cap, then fill the overflow tank to the cold line and watch the coolant level carefully.

If you are lucky, like willwren suggested, it may be just that the cooling system has trapped some air. It is pretty easy to trap a lot of air in these engines. We recommend a specific fill procedure to avoid the problem:
http://www.bonnevilleclub.com/forum/...=article&k=100

you need to follow the above, making sure the radiator is completely filled and refill the overflow tank.

For now assume the wisps off the radiator is coolant burning off that they spilled onto the radiator while flushing.

You need to let the car get fully up to temps too. if you dont the thermostat wont open, allowing the coolant to flow through the block/radiator. Which could yield more air bubbles being purged.

Keep an eye on it. If you really are buring coolant then you should be able to smell it in the exhaust.

Thanks for the comments so far.

At this point, I have topped up the radiator (it was down 3 cores) and the reservoir. I've taken the car on a few longer spins, but I don't want to get too far in case there'* a failure lurking.

I read your fill/bleed procedure, but the mechanic who did the work didn't do that, although he says he followed the "normal factory procedure." Hope that'* better than the normal factory UIM.

So far the coolant level seems to be holding steady. I'll try to fit in a 10-mile round trip later this afternoon. I can't tell how the exhaust smells, I lost my sense of smell during a bad sinus infection last summer. :( There is some visible whitish exhaust, but no more than most other vehicles I see on the road. There does seem to be more when I first start the car cold, as soon as the car warms for a few minutes the exhaust seems to get back down to normal.

This is all so subjective... grrr.

Thing is, if there is a large air bubble trapped in the intake manifold, it can prevent coolant from contacting the thermostat. If the air bubble is really big, it can prevent coolant from contacting or continuously contacting the coolant temperature sender as well. This can result in erratic or incorrect temperature gauge readings. When trapped air prevents coolant contact, the only way the thermostat can open is through heat conduction of the hot metal around the thermostat and through the inefficient contact of the heated air on the thermostat pellet. Unfortunately, the thermostat is insulated with a rubber flange gasket. So, the engine will need to get much hotter than it should for the thermostat to crack open. A primary cause of this problem is the lack of an air bleed in the stock thermostat. An air bleed is provided above the thermostat in the upper hose fitting, but that is only effective as a bleed when the thermostat is open. That is why we recommend a small hole be drilled in the thermostat flange to allow a path for trapped air to escape the intake manifold into the upper radiator hose and radiator.

Fill procedure for my 98 motor in a leSabre
is to bring the system up to temperature so that the lower radiator hose is warm and then to race the motor to 2500 rpm 5 times to force the air out of the heater core.

There also is a bleed screw on top of the thermostat to let the air out there-carefully by loosening it slightly and slowly until the air comes out and coolant drops appear.

After you have driven the car for 10 miles or so, feel the top radiator hose. It gets hot when the thermostat opens allowing coolant to flow into the top of the radiator. Once that hose is hot, revving the engine and opening the bleeder will help to remove trapped air.

Kind of makes you wonder why there'* no bleeder on the UIM.

I'll print this out and share it with my mechanic, and see what he says. I don't want to pull the stat and drill it, and risk voiding any warranty on the manifold/gasket job he just did. If this is OK with him, it sounds like a good idea to me. Thanks for the clear and detailed explanation, I'm sure I couldn't begin to convince him without that.

You might want to print out the Techinfo article on filling the L36, too. Even if your mechanic says it is a lot of unnecessary work, he may try it on the next one, and find out, like we have, from experience, that it works.

http://www.bonnevilleclub.com/forum/...=article&k=100

When you follow those instructions, and fill the engine at the thermostat housing first, you will see and hear slug after slug of air pushed up through the coolant in the LIM as coolant is added at the radiator neck. As you watch the air bubble up and out at the thermostat opening, it becomes pretty clear that with an undrilled thermostat tightly in place, air would have been trapped in the LIM right under the thermostat.