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Neal, Cadillac Mechanic
Category: Cadillac
Satisfied Customers: 8351
Experience:  Shop Owner and Mechanic on multiple makes.
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Northstar engine still running hot, could it be the water pump??!!

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Northstar engine still running hot, could it be the water pump??!!

I'm Neal and I am here to assist you. Only accept when you are happy with my assistance. If I can't help I will open your Question to other experts.


Were the GM coolant tablets used? It would be unusual for the pump to be the problem.




This question will remain open and I will continue to work with you even after you accept. The question will remain active for 7 days after our last communication.

Customer: replied 5 years ago.
No, I did not use GM coolant tablets. Are tablets supposed to be used? My problem begin after I changed my cooloant tank a couple of months ago. My sensor in the tank was bad, so I bought a new coolant tank since they don't sell the sensor separate.
I noticed right after that, I started having problems.
And the reason why I thinks it might be the water pump is because the car has 236K miles and I can't feel any coolant flowing thru my top hose. The hose is very hot and has expanded.

I f you feel there is no, or reduced flow then I would change the pump to be safe.


If the system was flushed the tablets should be used. They go in the lower radiator hose and dissolve and seal imperfections in the castings of the heads and block. But in your case you might try a product called Blue Devil, I have had tremendous success in cases even worse than yours. It is a high end block and head gasket sealer. Most parts stores carry it. Make sure you follow the instructions and chances are extremely good it will fix your issue permanently or at least for a very long time. They advertise a 85% success rate in Northstar engines. Here is a link to the manufacturer if you want to read more about it.

Customer: replied 5 years ago.
So you believe based upon the info I have given you, that I might have a fracture in the head that is causing combustion gas to leak into my coolant? And you don't believe its a water pump issue?

I believe the pump is a possible cause, but it is unusual and head gasket and casting flaws are more common. These issues are common on these engines and it is rarely the water pump.


When it was flushed, did the radiator seem to flow well?

Customer: replied 5 years ago.
Yes it did, also I noticed the heater blowed hot air while I flushed it, but now I get not hot air thru the heater, it blows only cool air.
The lack of heat would indicate either a lack of flow or air in the system. But if it pressure tests good and has no leaks there should not be air in it. So you might be right in your suspicion that the pump is the problem.
Customer: replied 5 years ago.
How do I get the air out of the cooling system? I am remembering that this problem actually started after I changed the coolant tank. Could I have allowed air to get into the cooling system, even after I flushed it?
If the cooling system is sealed it will purge the air itself as it cools down as long as pressure is not released. Usually 2-4 hot to cold cycles will do it.
Customer: replied 5 years ago.
Ok, I just had it confirmed by the shop after running a test of the cooling system, they believe I have a leak in the head gasket. Pressure is building up in the radiator. Now my next question is do think Blue Devil treatment can fix this?
Blue Devil is supposed to work 85% of the time in Northstar engines. I would sure give it a try.
Customer: replied 5 years ago.
Ok, thats my route next, one more thing, do I put the Blue Devil treatment thru the coolant or thru the lower radaitor hose? It says to remove.the thermostat. It has to free flow.

Follow the instructions exactly for the best results, add it just like adding coolant, make very sure you leave enough room for it after adding some coolant first.

Customer: replied 5 years ago.
Well I hope I got the right one because it saysd take all the coolant out, remove the thermostate and add the solution, then fill with "water". That stays in there while the engine runs for a number of minutes, then flush and fill with coolant.
Yes that is the right one, I was being generic when I said "coolant"
Neal and 4 other Cadillac Specialists are ready to help you
Customer: replied 5 years ago.
I was just waiting to see what the Blue Devile treatment would do, well it seem to work for about 45 minutes, then it began to run hot again. I followed the instructions to the "T".
The end result, find another motor, this one is gone!!!!!!!!!!!!!!!.
Thanks for all your help, I really appreciated it.
Customer: replied 5 years ago.
How difficult is to swap out a NS engine and labor and time factor?

It is a fairly difficult job and the book calls for 16.4 hours of labor.


It is not something you want to do without a lift.

Customer: replied 5 years ago.
Wow!, Well thanks I need to get on the job.
You're welcome!!
Customer: replied 5 years ago.
Good morning Neal, if you have a minute please help me out. I'm anout to get another engine when I was asked by the seller exactly what is my engine doing. Absent of "white smoke" coming out the tail pipe, no water mixed with oil, and mot running hot while idling, that I may have a clogged up coolant system, coolant not flowing thru the radiator properly. The top hose get rock hard.
Do you think he might be right. He said that the Blue Devil sealant woild have fixed the leak. So it may not be a leak, but a blockage. Is that possible?

I think we discussed that early on or I at least mentioned it might be a blockage.



One possibility is reduced radiator capacity. Over time the radiator can collect sediment that cannot be flushed out. To check this get the engine up to normal temp and turn it off and then being careful of the fans which can still turn on, compare the temp at the bottom of the radiator to the temp at the top of the radiator, if it is much colder at the bottom than the top, or there are any areas that are cold, that is a sign it is partially plugged and the capacity is reduced.

If available you can use a non-contact thermometer.