New to me 1997 Deville w/Northstar 4.6. 128K miles. The car is fine around town at speeds of 25-45 mph. On the highway, the temperature rises fast and the car overheats. The car looses 1 - 1,5 gallons of coolant when this happens. I don't know whether the overheating is caused by a sudden loss of coolant or I am loosing coolant as a result of overheating.
I really fell like this car could go from New York to California at 30 mph but not 10 miles at 70 mph.
Temperature will rise to 230+ if idle is held at 3000 or above while stationary but will not reach the 260 the car hits when overheating on the highway.
I have tried replacing the thermostat and radiator cap. I used bar's leak when refilling.
Have you checked the water pump drive belt and the small tensioner on it to make sure the belt is good and the tensioner is keeping the belt taut...??
The water pump is driven by a separate small belt on the back of the intake cam on the left bank......
Did you put the sealant into the radiator hose?? If you put it into the surge tank when refilling then it may have clogged the hose from the surge tank to the water pump inlet. The sealant needs to be put into the rad hose directly so that it is exposed to the bulk flow of the cooling system so as to disperse correctly. If it was put into the surge tank then you might need to disconnect the 1 inch heater return hose at the thermostat housing and flush the hose out from the surge tank .
Wow. That is insightful. Yes, I checked the waterpump tensioner and belt and both seem ok to me. Though, the water pump does turn much slower than the crank driven accessories.
Also, yes, someone (not me) broke up the bar's leak pellets and dumped them into the surge tank. Yesterday, I cleaned out the surge tank by disconnecting the lower hose at the tank and flushing the tank with a hose. I got out a LOT of brown mud which I believe to be the bar's leak which had just stayed in the surge tank.
Is the 1" hose you are talking about the hose which runs from the top of the surge tank across the intake? I did not flush that? Should the whole system be flushed?
I taped a 20oz diet coke bottle to the end of the pressure tank escape hose and took it out on the highway. It overheated as usual, filled the bottle and blew it off the hose. At least I know all that coolant is going out the hose and not through the motor. Next step is a thorough flush of the whole cooling system.
Wow. That is insightful. Yes, I checked the waterpump tensioner and belt and both seem ok to me. Though, the water pump does turn much slower than the crank driven accessories.
Also, yes, someone (not me) broke up the bar's leak pellets and dumped them into the surge tank. Yesterday, I cleaned out the surge tank by disconnecting the lower hose at the tank and flushing the tank with a hose. I got out a LOT of brown mud which I believe to be the bar's leak which had just stayed in the surge tank.
Is the 1" hose you are talking about the hose which runs from the top of the surge tank across the intake? I did not flush that? Should the whole system be flushed?
The hose you are describing is about a 3/8 hose I think..... That is the vapor vent hose. Disconnect it at the surge tank when the engine is cold and start the engine. You should observe a steady stream of coolant peeing out the hose towards the surge tank fitting. If not, the vapor vent system is not flowing and the plug needs to be found and corrected. If you look at the upper radiator hose at the engine end you will find the other end of the vapor vent line where it exits from the engine. Take the hose off there and see if the fitting (which is really a hollow bolt) lets coolant escape from it with the engine idling. The vapor vent line must be flowing coolant to allow the water pump to vent any vapor that gets trapped in it. Otherwise the water pump will vapor lock....if the vent line is flowing coolant then it will automatically purge any vapor from it.
The 1 inch (ID) line is the hose at the bottom of the surge tank that goes to the water pump inlet fitting. I would disconnect the 1 inch hose at the water pump inlet and flush thru from the surge tank to make sure that that line is clear. Otherwise the pump can cavitate if it cannot "see" the pressure from the surge tank.
The water pump itself should never be able to cause overheating. It can leak and the bearing can start to fail and make noise but as long as the pulley is turning the pump impeller will turn and pump coolant.
Double check the water pump belt and tensioner to make sure that the tensioner still moves freely and tensions the belt correctly. Sometimes the tensioner can corrode at the pivot and stick causing it to not put any tension on the belt.
It looked to me like that 1" hose goes right into the block on the right (passenger) side. Does it run around to the other side of the engine where the waterpump is, or is the waterpump inlet on the right side of the engine?
Could it be a leaking head gasket causing exhaust gas to pressurize the cooling system and force coolant out through the surge tank escape hose? Why wouldn't that happen at 3,000 rpms in the driveway as well as on the highway?
Yes, that 1 inch hose from the bottom of the surge tank runs around the right bank of the engine where it tees into the heater return and then goes to the water pump. The water pump is at the rear of the engine and the cover on the water pump is the pump inlet. You will see a large hose from the rad on the cover and a 1 inch hose....that is the other end of the hose from the surge tank.
Have you checked the thermostat to see that it is opening completely. If it is getting lazy then it could not be opening enough to allow the engine to cool.
The other thing to do is to check the radiator for flow. You can usually feel across the rad for "cold spots" to see if there is any plugging of the core but taking the tanks off and inspecting is the only sure test.
Yes, it could be a head gasket......
Often the engine has to be under some load to develop sufficient cylinder pressure to force past a leaking head gasket if the combustion seal is failing. Just revving to 3000 in neutral does not generate much cylinder pressure at all due to the fact that the engine is so heavily throttled just free revving it.
If you suspect a head gasket there are a couple of tests to run to confirm.
Fill the cooling system and idle the engine. Watch the surge tank for signs of bubbling from combustion gases. Since you are not seeing problems except under load this is not conclusive at all.
Pressurize the cooling system with a coolant system pressure checker. Leave the system pressurized for several hours. Keep pumping it up if the pressure drops. Meanwhile, pull the spark plugs. After a few hours of cooling system pressure crank the engine over with the starter with the plugs out. Watch the spark plug ports for coolant spewing out. If a head gasket is leaking coolant into a cylinder you should see coolant come out a spark plug port.
Make an adapter out of an old spark plug shell and use it to hook shop air at 120 PSI to the spark plug port. With the valves closed watch the coolant in the surge tank while the cylinder holds 120 PSI for several minutes. Do this to each cylinder. This is the best test by far for determining if you have a head gasket leak and which cylinders are the problem. This is really the only conclusive test in my opinion.
Ready for the bad news....BLOWN HEAD GASKET.
I just got done repairing my '97 Seville. I had the same problem you're describing. I have 134K on my car. The #7 cyl. is usually the one that gives way. It's right above the front exhaust pipe that comes up between the engine and the trans. The pipe overheats that cyl. and weakens the alum. block. The aluminum block weakens and the head bolts pull the threads out of the block. You have to Threadsert the block (insert oversize threaded sleeves) into the head bolt holes. Email me and I'll help you with where to get all the parts.
Easiest way to test is to heat the motor up, rev. to 3000 rpms, does the upper radiator hose get real hard? Shut it off... is the water in the hose boiling? Remove the rad. cap, can you smell exhaust fumes in the overflow tank? If yes to all....it's a blown head gasket.
can you tell me why my car over heats some time and then when I turn it off and let the motor cool down when I turn it on again it woks fine
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Cadillac Owners Forum
4.8M posts
369.7K members
Since 2002
Cadillac Forums is the perfect place to go to talk about your favorite Caddys including the ATS, CTS, SRX, Escalade, LYRIQ, Vistiq, concept and future Cadillac models.