Engine overheating/cooling problem

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Hey all,

ok this a bit of a story so please bare with me, and I hope it is alright if I have a couple questions in the same post as some of it may be related.

1993 pontiac sunbird 4-cyl, 2.0L OHC, automatic transmission.

I will start my story on the drive home from the used car dealer. It is about a 45 minute drive from this place to my house and some of it is on the freeway (100km/h speedlimit), anyways, as I was driving the oil pressured dropped and I ended up blowing up the engine(saving the details as this has nothing to do with the problems I am having. Ok, so a few days later I have a used engine delivered to my house from an autowrecker (from 1992 pontiac sunbird) The engine is exactly the same except for two parts, the oil pan on the original engine has a sensor? of some sort wired to the front side of it, and the diptstick carrier from the replacement engine has a curve at the top where the original carrier is straight.

I went through and swapped engines with minimal problems, and here is where I really started to have problems. During the swap I put in new oil filter, air filter, thermostat, thermostat housing cap, and spark plugs. After test driving the car a few times I noticed some coolant leaking from what appeared to be between the cylinder head and the block. The Idle Air Control Valve also died at this time causing the engine to idle at very high speed, and I noticed the oil light was on even though the dip stick said there was sufficient oil. So I replaced the head gasket and the IAC and when I went to start the engine it was very difficult to start and died shortly after... this is where I thought uh oh, I really fouled things up this time :banghead: well after a very frustrating week of troubleshooting, I found that I must have got some impurities or moisture in the fuel line as my fuel filter was clogged. :banghead: After replacing the fuel filter, the engine started instantly. (oh i did have the car running long enough to heat it up so I could finish tightening the head bolts).

So everything is honky dorey right? wrong!!! Whenever I start the car cold the oil light comes on, but if I turn it off right away and start it back up, the oil light goes off (the oil light does not turn off until I turn the car off and start it up again, it does not matter how long I let it run, and the dipstick never lies, there is sufficient oil). So I heat the car up and check for leaks as should be done whenever doing some of the work I did, and after some time of running the car, the check engine light comes on, :banghead: and the car starts idling erratically. Well, I checked the engine troubleshooting codes and then replaced the O2 sensor, and voila no more engine light and erratic idling. Still have a problem with the oil light (you think it has something to do with the sensor on the original oil pan?).

Anyways, I took it on a test drive and discovered a coolant leak from one of the hoses and I tightened the clamp fixing that problem and here is where my new problem comes into effect, the first test drive after fixing the coolant leak the engine temperature went up fairly quickly to just before the red line (maybe took about one minute) and then dropped back down to just above the bottom of the guage, and then it went back up, and then back down... it continues to do this as long as the car is running, sometimes the temperature reaches the red line and the check guages light comes on for a second or two and then the temperature drops again. I tried turning on the heater (as I live in canada the heater can be an important part of the car) and all I got was cold air blowing through.
Coolant level is good, and I am not losing any more coolant.
Oil level is good, and I am not losing any oil.
So if someone could please let me know what the problem is I would be eternally gratefull?


P.S. I will ask about the brakes in a new thread.

posted by  cyberdeck

Not that it helps, but that part was funny. I knew what was coming next :laughing:

posted by  DodgeRida67

How is the ignition timing? (if not electronically controlled with I doubt it is)

posted by  DodgeRida67

Timing is distributorless and is controlled by the computer with input from various sensors including the crankshaft position sensor.

posted by  cyberdeck

Thought that for a second or so, but didn't think it had it but I now know it does.

Hows coolant level? Thermostat the right opening temp?

I'm thinking the thermostat is bad, or the wrong temp. I'm thinking this because of the way to temp goes up, then maybe the thermostat opens then the temp drops. Thermostat closes, repeats the process.

posted by  DodgeRida67

low coolant level will also cause the gage to act similar to the description - creates an air bubble. Remove the radiator cap fill the radiator to the top then close it. next make sure the coolant recovery bottle is to the full mark. Drive the car a couple of times and top off the bottle.

You probably have two different oil sending units an oil level light and an oil pressure light or gage.

The sending unit at the side of the oil pan is an oil level sending unit. Some cars have an idiot light on the dash which lights up if the oil level gets too low. This unit has nothing to do with oil pressure

Your oil pressure sending unit should be mounted in the block near the oil filter (passenger side rear of engine).

If the OIL PRESSURE light is flickering on, check the pressure with a gage. If the pressure is OK with a gage, make sure the wiring is OK then replace the sending unit. If you have an oil pressure gage, the above test will work as well

If the problem is the OIL LEVEL idiot light, check the oil - if oil is OK, then replace the sending unit or level switch.

posted by  tbaxleyjr

Ok so the coolant was not low but there was probably an air pocket somewhere in the system. I ran the engine for a few minutes without the thermostat and let the system cool down. After cooling the coolant in the bottle was low, so I replaced the thermostat and filled the bottle back. Everything is running great now, Thanx.

So if I understand you correctly, the computer thinks there is no oil in the system for two reasons until the car has started and then stopped. First the oil level sending unit is non-existant because the oil pan on the replacement engine does not have one (I will switch oil pans when I do my next oil change). And second is probably because the oil pressure guage was probably a dummy light on the original vehicle that the replacement engine came from and therefore the sending unit probably acts accordingly where as the original engine has a pressure guage sending unit and the computer is probably trying to interpret mixed signals (I will put in a new pressure guage sending unit when I do my next oil change). Thank you for your help, I would have been banging my head for a very long time before I would have figured this one out. :thumbs:


posted by  cyberdeck

Fortunately, the ECM has nothing to do with either sending unit.

If your car has gages and the sending unit in the replacement engine was for an idiot light, the sending unit will need to be swapped to one compatable with the gage wireing for your car. I think, the threads in the block are the same for either unit. If by some screwy, odd ball chance they are not, an adapter can be boght inexpensively.

If your car had an oil level light or an change oil light and the replacement engine did not have a port for the sensors, if you want those functions, you will need to use an oil pan with the right sensors such as the one from your 93 if it fits.

posted by  tbaxleyjr

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