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Steve
Steve, Auto Service Technician
Category: Car
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Experience:  25+ yrs experience as a professional working technician; ASE L1 master technician
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1993 Olds: me the head gasket was blown..swapped..started right

Customer Question

1993 Olds royale 88. Previous owner told me the head gasket was blown. I swapped a 3800 engine fron a 93 bonneville It started right up but quickly overheated. Thought fans had failed but by passing the switch made them work fine. Dashboard gauge stays pegged at 280. so engine will not start. have traced circuit for short but find none. Does this circuit pass through the ECM? any other suggestions would be appreciated.
Submitted: 11 years ago.
Category: Car
Expert:  Steve replied 11 years ago.

The cooling fans on this vehicle are controlled by the PCM; the component you are jumpering is not a fan switch (it does not have one); it is likely a coolant temperature sensor. The PCM uses the coolant temp sensor to adjust fuel mixture and sprk advance, so by disconnecting or jumping it you may be creating the no-start condition.


If the engine is truly reaching 280 degrees as the gauge says, tehn it is indeed overheating and you will need to determine why. If it reaches 280 degrees when the fans are running, then the fans are not the problem. Have you checked for a stuck thermostat? ALso, this engine has t have a 50/50 mix of antifreeze and water. It WILL overheat if it is run with straight water in the cooling system, as the primary fan on most GM engines does not turn on untill around 220 degrees, which is past the boiling point of water.


Here is a schematic of the fan wiring so you can see how it all works:


Expert:  Steve replied 11 years ago.

If the previous engine blew a head gasket, then tehre is a possibility that the radiator may be defective in this car also. The usual reasons for head gasket failure are: (1) failure to change coolant, which can result in deposit formation and/ or acidic coolant damage to the radiator and (2) overheating due to a stuck thermostat, coolant loss, or other engine problem.


(1) You will need to use a scan tool to see what the computer is reading engine coolant temperature as. If it is above 220 degrees, then the computer should be commanding the fan relay on (this will be shown on the scan tool as fan status, or something similiar). Take a thermometer and directly measure the coolant temp in the radiator neck; if it is not close to what the computer is seeing, try replacing the coolant temp sensor.


If the coolant temp is over 220, and the computer is commanding the fans on, tehn you will ened to start troubleshooting the fan circuits to find the problem.


(2) Assuming teh coolant is reaching operating temperature (over 195F), you should tehn see the coolant begin to circulate in teh radiator when teh thermostat opens. If you do not, then you either have a thermostat stuck closed, or a faulty water pump. Also, make sure you ahve installed the belt correctly; a pump being turned backwards by incorrect belt routing will make a car overheat (yes, it is possible; we've all done it at one time or another!)


(3) If coolant is circulating, then check for a restricted radiator: using either a temp gun or your hand, check the tubes in teh core for sections that are cooler than others, which might indicate restricted flow.


(4) make sure that youa re not using pure water in the system, for reasons previously described.


Expert:  Steve replied 11 years ago.

Note: Turning the AC on should make the fans operate; they should run whenever the compressor is engaged. This will tell you whether the PCM has control over the hi speed fan circuit or not...


Following is some diagnostic information from teh service manual which may be helpful to you:



Expert:  Steve replied 11 years ago.
Expert:  Steve replied 11 years ago.
Expert:  Steve replied 11 years ago.
I hope this information is helpful; if I have answered your question, then please click on my accept button! If not, please let me know what other information I can provide for you, to make my answer acceptable. Thanks!

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