Coolant Boiling Over On 1996 Oldsmobile Aurora

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1996 Oldsmobile Aurora. Check engine light VSS, and EGR valve. Bought car in this condition. Doesn't overheat per say, but was running hot to me at 250 degrees. Replaced radiator.

Question: I pressure checked system at 15psi for 15 min. held steady. I drove for a couple of days, and was loosing coolant. Found the radiator tank cracked on left side. (funny pressure test didn't find this. Replaced radiator and still runs at 250 and pukes a little coolant out of the overflow.

Though when I get done driving 20 miles home from work, and check fluid it is just low, not blowing out like when the radiator was leaking. I checked fan relays and they are good but when the fans do come on which takes forever, they both turn on , but slow. If I pull out relay and jumper I can get it to go fast. So I'm guessing a high speed fan relay or temperature sensor is bad? I would think at 250 degrees the fan would spin faster.

Also another problem I have is the Instrument cluster stops working intermediately. Would this be the Body Control Mod? I pulled it apart and it is getting hot a large resistor looks like its kind of burnt. Thanks for any help you can give me!

ANSWER:

Hello and welcome. OK. Allot to look at on this one. First, these engines are know for have head gasket problems. Does not always show up with pressure tester, just as radiator cracked did not. Letting idle long till gets hot, looking for bibles in surge tank, then revving up motor and looking for coolant to come rushing out is a sure sign of headgasket blown.

Fans electrically. The three relays work together to work the fans. Be sure all fuses are good. Low speed relay is on the firewall, left or the wiper motor.I will attach a diagram and circuit description in another e-mail in a few moments. Yes, sounds like you got the problem with that burned bcm.

Engine runs hot at idle. Fans only comes on when air conditioner is on.

Check your coolant temperature sensor. It may not be giving the correct temperature to the computer. The fans will come on with the A/C no matter what the coolant temp.
Both fans run at the same time and the same speed. Fan relay #1 on gives you low speed. All 3 relays on gives you high speed. Relay #2 puts the fans in series (low speed) or parallel (high speed). Low speed is triggered by engine coolant temp greater than 229F or transmission oil temp greater than 302F or AC on. Fans turn off when temp drops below 216F High speed is triggered when engine coolant temp exceeds 234F or transmission oil exceeds 304F. Switches back to low when engine coolant temp drops be low 229F.