Engine temp rises quickly (intermittent) to overheat. Yet, when you open the hood it is not hot under the hood and fans are not running. Shut down for 5 seconds and restart and you get engine temp at about 217 and will cool to 199-205 depending on outside temp. You can keep driving until this happens again.
Bad temp sensor or wiring harness issue.
SOURCE: 1998 Cadillac Deville overheating
The most common overheating problem with the Northstar engine is a blocked purge line. It's job is to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.The hose goes in to the engine to a crossover and comes out the other side to near the thermostat housing,the blockage may be there.
SOURCE: 98 deville 32 valve North Star OVERHEATS after 33
The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.
Also note that the cooling fans don't come on until the coolant temperature hits around 225 degrees.
During normal highway driving the fans will very rarely come on(if at all) due to constant air flow through the radiator.They will only usually come on in heavy traffic conditions on a hot day.
But......if you have the Air Con switched on, the fans will run all of the time.
SOURCE: 99 cadillac deville engine overheating an loosing
Check to see if you have flow through the entire radiator.If part of the radiator core is cool to the touch when the engine is at operating temp, this indicates restricted radiator flow. If the entire radiator core is not allowing water to flow through, cooling will not be at all efficient. Also a good idea would be to purchase a block tester. available at napa and other reputable parts houses for around thirty dollars. You remove a small amount of coolant, and put the tool in the radiator, or pressure tank opening. If there are any combustable gasses present, i'e' exhaust, this would indicate a head gasket breech, (or maybe worse) and would indicate that it's time to stop looking for a simple problems, and get proffessional help. Good luck to you!
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