Boil over

Tiny
88
  • MEMBER
  • 1988 CHEVROLET CAPRICE
  • 5.0L
  • 3 CYL
  • RWD
  • AUTOMATIC
  • 120,000 MILES
Previous questions involved a starting problem cured by a distributor tune up, a fast idle problem remedied by allowing the engine to warm up fully before driving it, and a lack of acceleration with poor gas mileage which remains unsolved. Now, the last time I drove it was to do a quick shopping nearby and get gas. On the way home I heard it knock going up the first hill for a quick moment, it was very slow going up my rather steep driveway, then it boiled over when I turned it off. This was a first. Usually the temp never goes over half way on the gauge. Could this be related to the acceleration problem we discussed previously which we determined Keep in mind, I did hear a knock momentarily going up the hill. Could the timing chain have gotten so loose it skipped a tooth and jumped time? What else could it be?

Should I stop driving the car until this is sorted out? Is it likely to boil over again the next time I use it?

The only thing that changed prior to the boil over is that I had a mechanic check it out the day before to see if he could determine what the performance problem was. He drove it, took off the air filter, checked the carburetor and a few things on the top end, used a vacuum device to check out some kind of ports for clogging (carbon fouling) and then told me he did not know and the car would have to go through a full diagnostic to find out. Could not he have at least checked to see if there was a delay between the rotation of the crank pulley and the rotation of the distributor rotor to see if the chain might be stretched? I cannot do it because I have no one to help me look at the rotor while I turn the crank pulley.

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Sunday, May 28th, 2017 AT 9:08 AM

12 Replies

Tiny
HMAC300
  • EXPERT
First thing is it is a thirty year old car it will have some timing chain stretch just because of that. pressure check coolant system to see if any leaks like a head gasket . if not it may be a bad thermostat or radiator. as far as knock sensor not even sure your car has one as it's early obd 1 and may be a part time system. check your fuel pressure with a gauge auto parts rent it. start there first along with scanning for codes. See link.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Monday, May 29th, 2017 AT 6:23 AM
Tiny
88
  • MEMBER
I was watching the mechanic and some of the procedures described in the article (which was very precise and I thank you for it) were familiar. He put a pressure gauge on it and a vacuum device as well as check the externals on the carburetor.

As for a head gasket, would not that be accompanied by noticeable steam from the tailpipe as the heat from the combustion chamber super-heats the coolant as it is drawn into the chamber? There was no steam from the exhaust. Also, I started the engine when it began to boil over into the overflow tank to try to circulate the coolant through the radiator in hopes of cooling it down enough to stop the boil over. The temperature did come down some but boiled over again after I turned it off. There has been no evidence of coolant beneath the car.

Would this performance problem (possible timing chain) be related to this overheating? With the engine malfunctioning as it has been, could this have caused the overheating problem? Or, could I have not been paying attention to the temperature gauge and could an overheating problem have been occurring this whole time and causing the performance problem?

88
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Monday, May 29th, 2017 AT 10:24 AM
Tiny
HMAC300
  • EXPERT
The timing chain is normally not associated with loss of power from a head gasket. From your description I will still go with a head gasket. If it leaks outside the engine while driving would not throw steam if not going into cylinder.
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Monday, May 29th, 2017 AT 12:58 PM
Tiny
88
  • MEMBER
No, of course not. My question was whether the stress of driving the engine in this condition (whatever the reason for the lack of performance), especially up the rather steep hills in my neighborhood, could have contributed to the overheating problem. My second question was whether the same thing that could cause an overheating problem also cause the performance problem I described. My guess is that a head gasket breach would cause both with the electronics complicating things by trying to compensate for the shortcomings (in essence, covering up the problems). However, the performance problem came months before it overheated yesterday and I can find no indications of a blown head gasket.

88
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Monday, May 29th, 2017 AT 2:39 PM
Tiny
HMAC300
  • EXPERT
The low performance is from the head gasket period as well as overheat and if you put any strain on the engine about the only way you could put any strain on the engine is if you pulled a car with similar weight up the hill. I have sent the replies that I feel from your description is the problem with your car which is two fold. Re read my very first reply.
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Monday, May 29th, 2017 AT 3:10 PM
Tiny
KEN
  • ADMIN
Hello,

The first thing I would look at is a stuck thermostat causing the overheating.

https://www.2carpros.com/articles/replace-thermostat

Please let us know what happens.

Cheers, Ken

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Monday, May 29th, 2017 AT 3:40 PM
Tiny
88
  • MEMBER
Thank you both for your reply. If the thermostat was defective, would the temperature still go down when you start the engine again during the boil over (which occurs only after the engine is turned off after a run)?
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Monday, May 29th, 2017 AT 5:39 PM
Tiny
HMAC300
  • EXPERT
If a tstat is bad it will either overheat within a few minutes of starting or not reach temperature if stuck open.
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Tuesday, May 30th, 2017 AT 5:20 AM
Tiny
88
  • MEMBER
OK. Thanks to you both. Then it's not the thermostat. I looked into the troubleshooting section of my repair manual because I had a distant memory of something relating to timing and temperature. It said, under overheating (among other things) "Ignition timing incorrect." This would correspond to the lack of acceleration and the lack of power going up hill as the car tries to accelerate under a load while the computer retards the spark trying to prevent knocking, would it not? This may also account for why the car diesels when you turn off the ignition, wouldn't it?

The distributor has been serviced (except for the sending unit that can only be changed by removing the distributor), the wires are all plugged in properly, the engine seems to run smoothly and quietly. As HMAC said previously "the car is 30 years old" so it's likely the timing chain is stretched some. I've read and seen on video where loose chevy chains have actually jumped a tooth throwing the ignition out of time and as HMAC has said, a stretched chain will throw off the valve timing.

As much as I've tried to find ways to avoid it, it looks like I got a job ahead of me. What do you think? Could there be any small, easy thing(s) I've overlooked that could account for these deficits?

88

PS: If it is a head gasket, what external signs (if any) should I look for if there is no steam coming from the exhaust? Thanks.
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Tuesday, May 30th, 2017 AT 11:21 AM
Tiny
HMAC300
  • EXPERT
I didn't say it would throw off valve timing I said at car's age and mileage there is going to be some stretch. External leaks would be minimal and leak down side of block or at rear.
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Tuesday, May 30th, 2017 AT 12:02 PM
Tiny
KEN
  • ADMIN
Here is an easy way to see if the head gasket is blown run this test and get back to us.

https://www.2carpros.com/articles/head-gasket-blown-test

Please let us know what happens.

Cheers, Ken

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Tuesday, May 30th, 2017 AT 1:03 PM
Tiny
88
  • MEMBER
Thanks to you both. Link was very good. Will conduct tests as soon as I can and let you know.

88
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Tuesday, May 30th, 2017 AT 1:55 PM

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