Engine over-heating; runs rough; back fires

ALETA SONNENBERG

MEMBER
BUICK SKYLARK

1991 Buick Skylark 2.5 sedan 89,000 miles. When I bought it, it had a cracked manifold. I had that repaired. It ran very smoothly and obtained 28 miles per gallon fuel economy. Then last winter the radiator sprang a leak. I had that repaired. When we picked the car up from the radiator repairman, he commented that he thought we should get a "tune up" on it because it was running so rough he could barely test drive it after the repair. Indeed, it ran and idled incredibly rough and now the heater was not giving heat. I talked to an auto mechanic who said he thought that the radiator repairman, when he flushed the radiator, had plugged some of the conduits (tubes or whatever) that allow the engine heat to transfer to the heater. (I may not be reporting this accurately, as I did not quite understand what he was describing to me). I talked to the radiator repairman who denied any responsibility and asked if I was accusing him of careless work. The weather by now has warmed up. I took it to an auto repair shop for the "tune up" suggested by the radiator repairman. There the mechanic put in new spark plugs, distributor cap and rotors, replaced the air filter and a pinched air hose. It still ran rough and was now overheating. He suggested that we replace the thermostat, which we did. It runs rougher than ever. I cannot drive more than about thirty miles without the coolant boiling or sometimes blowing the reservoir. It runs so rough now that it is losing power going up the steep hills in our town, barely making it to the top even with the accelerator fully depressed. When I press down on the accelerator to gain more speed or power, I get less. At one intersection, whenI pressed the accelerator to merge into traffic I was nearly broad sided because of sudden loss of power. Besides the loss of power there was lots of backfiring in the exhaust system just like there is when going up hill. Putter putter putter POW POW putter putter putter POW POW and then (sometimes) a little more power. I am at my wits end to know what the problem is or to whom to take it for repair. I am only getting about 12 miles per gallon now and can still only drive about thirty miles before stopping to let it cool completely. What now? What do I do?

3 Replies

MIKEYBDMAN

MECHANIC
623 POSTS

A couple of questions.
Do you have to keep adding water?
Have you had the compression checked?
Have you had the intake Manifold inspected for cracks?
It almost sounds like you have a cracked intake of Cylinder Head. Hopefully a compression check will show where it is cracked.

Here is my take. If it was just a overheating problem, then I would look at the coolant components. But since you have running issues also, that makes me believe you have problems in the engine. Rough running like you describe does sound like a intake manifold leak.
Not sure how mechanically inclinded you are, but to replace the intake is not that hard of a job. Probably take you around 4 hours, or longer if you havent done it before.
If this were my car, I would probebly remove the intake and cylinder head. Have them both checked for cracks and warping. Repair if possible, or replace if bad.
NOTE: before sinking time and money in this car, you might want to check the compression and see if you might have major problems. If the compression checked good, I might be tempted to just stop with the intake. But definantly stop when you find a problem. If the intake is cracked, dont pull the head unless you have low compression or obvious signs of problems with it.