Is 235 too hot for a N*star on hilly roads?
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Northstar Engines and System Technical Discussion Discussion, Is 235 too hot for a N*star on hilly roads? in Cadillac Engine Technical Discussion; I drive and monitor the cooling system in my 1999 base Deville as if it ALREADY has a blown headgasket ...
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    DanDeville99 is offline Cadillac Owners Member
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    Is 235 too hot for a N*star on hilly roads?

    I drive and monitor the cooling system in my 1999 base Deville as if it ALREADY has a blown headgasket from the stripped head bolt issue. The year and the mileage makes it a sitting duck for that issue at 110k.

    I run the green Peak any make and model antifreeze and just put 5 Delco seal tabs in the upper rad hose. It drives the normal operating temp 197-213 on the highway but if you really push it up mountains with the a/c on the temp will climb as high as 235 according to the digital readout on the base Deville cluster. This is driving it as if I WANT it to warm up and not taking any precautions like turning off the a/c or driving slow on STEEP inclines after driving the car at least 10 miles to know its fully warmed up.

    In the 1200 or so miles I have driven the car I monitored everything close. Sure enough, I was loosing coolant and achieved 255 degrees last week but was very relieved to find it was the lower coolant pipe leaking near the pulleys. I just assumed it was where the coolant tank boiled over and this issue went unnoticed a few weeks. A good friend of mine had the part in stock and the two of us changed it with the engine still mounted in the car. It wasnt fun, but possible.

    I plan to have the timsert job done WHEN the gaksets go but no sense in doing it any sooner than needed. I think I can even drive with the cap loose and get even more miles if needed.

    I dont take the car on long trips but go 30-40 miles from home with it and see no signs of a typical head gasket issue. Things like white smoke, hard starting, or oil and coolant mixing are not happening.

    I have found that filling the reservoir to the top will cause some to boil out and a few bubbles occur in the tank at idle with the cap off. These are the few things that lead me to believe I am in the early stages.

    Sorry that a lot of this was discussed in other posts but I wanted to get an idea on the 235 thing and driving this car with cap loose. It SEEMS like the exhaust in the coolant leak would help pressurize the system enough to keep it cool. I asked a guy at the Cadillac dealer and he agreed.

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    Re: Is 235 too hot for a N*star on hilly roads?

    DO NOT EVER drive it with the cap loose. That will lower the boiling point and will certainly cause a boil over. I can't believe anyone at the dealer would agree with that. Who did you talk to, the janitor?

    I agree, some of you symptoms sound like early stages. Others sound normal. If it is a head gasket, it will let you know soon enough.

    Might want to consider seeing Jake. http://www.northstarperformance.com

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    Re: Is 235 too hot for a N*star on hilly roads?

    Quote Originally Posted by Ranger View Post
    DO NOT E
    Might want to consider seeing Jake. http://www.northstarperformance.com
    Not too far from you at all and the best deal on saving the POS you have there.

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    DanDeville99 is offline Cadillac Owners Member
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    Re: Is 235 too hot for a N*star on hilly roads?

    Quote Originally Posted by Ranger View Post
    DO NOT EVER drive it with the cap loose. That will lower the boiling point and will certainly cause a boil over. I can't believe anyone at the dealer would agree with that. Who did you talk to, the janitor?

    I agree, some of you symptoms sound like early stages. Others sound normal. If it is a head gasket, it will let you know soon enough.

    Might want to consider seeing Jake. http://www.northstarperformance.com
    Hi Ranger,

    I agree with you, especially on a normal engine. I just assumed that the exhaust gasses getting into the coolant, IF that is the case, would help raise that boiling point back up. The car is driven in Upstate NY where it does not get too hot. I was standing at the parts counter at the Cadillac dealer and the parts guy asked a tech who walked in for a part. That is the best time to catch these guys when its informal.

    Thanks to the link to the site. I am going to try the test he mentioned. It may save miles of driving and a lot of gas.

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    DanDeville99 is offline Cadillac Owners Member
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    Re: Is 235 too hot for a N*star on hilly roads?

    Ok, I am a little more convinced that exhaust is getting into the coolant on this car. First thing cold this morning BEFORE STARTING I removed the cap and heard SOME pressure release. After 14 hours there should of been NONE? I had a feeling the car may still pass the test mentioned at northstarperformance so I took it to another level. I installed only a 7 lb cap on the car and hooked up a beverage bottle to the drain hose on the black tank. When I did the test about 3 times of getting up to 70 a few times, slowing down to 30 the car would not go past 228 degrees on an 82 degree day with the a/c on.

    Of course when I got home and opened the hood the beverage bottle was full of purged coolant but the car was not boiling. Before I leave again I will have to dump it back in and replace the 15 psi cap.

    I am thinking about making a minor modification that may allow even longer use of this car before the engine is torn down. Has anyone ever tried to connect the purge hose (the one that dumps on the ground when the cap lets off excess pressure) into a conventional NON-Pressurized overflow jug like older cars had? Then I could run the lower p.s.i cap, and increase my coolant capacity. Right now there is a fine line in the sand as to how high I can fill my black OEM tank. IF I exceed that, it just gets sprayed back out eventually. This way the excess goes into the extra jug, then when the car cools it MAY get drawn back in. IT all depends on the pressures but I think I could run the 7 psi stant lever lock cap if I had a place to recover the lost coolant.

    Again, if the HG's are blown, they are blown but I dont see the need to repair them yet if the car still gets me from point A to point B with a little bit of running on the warm side. The second I see white smoke or coolant in the oil, it gets parked to avoid bottom end destruction. I came into this car KNOWING it was a prime target for HG's. It sat around over the last few years and was driven very little with old Dex-cool still in it.

    By ANY freak chance has anyone ever discovered the cap to be bad? My other GM car that is also famous for HG trouble is a 3.4 venture van. I thought for sure it was done a year ago but it turned out to be just the cap. The system would build up extreme pressure and peg the gauge.

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    Re: Is 235 too hot for a N*star on hilly roads?

    If you are filling the surge tank over half full, COLD, it is way overfilled and will blow off coolant with every warmup. That airspace is there specifically to allow the entire coolant/system to expand and contract with temperature changes. Full to the top and it's no wonder the cap leaks. Coolant blows off, pressure drops and the coolant boils.

    A 50/50 mix of coolant/water boils at 218 at atmospheric pressure, 265 at 18 psi. A 70/30 mix (max concentration/GM approved BTW) boils at 218 and 276 respectively.

    Put the 18 pound cap back on and leave it there !!! It's no wonder you're having problems - the cooling system IS NOT designed to run at less than 16 psi. Yes there will be some pressure in the system after overnight, and if there is, the head gasket is not blown. Restore the cooling system to design normal and stop trying to outguess the engineers.

    The purge line is SUPPOSED to constantly bleed coolant back to the surge tank: That tank is also connected to the system at the bottom, and the purge line removes air and gasses from the coolant in order to prevent pump cavitation. Stick the purge line somewhere else and you pump all the coolant out !!!

    The coolant overflow line is dumping coolant because the system is grossly overfilled !!!

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    DanDeville99 is offline Cadillac Owners Member
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    Cool Re: Is 235 too hot for a N*star on hilly roads?

    Quote Originally Posted by submariner409 View Post
    If you are filling the surge tank over half full, COLD, it is way overfilled and will blow off coolant with every warmup. That airspace is there specifically to allow the entire coolant/system to expand and contract with temperature changes. Full to the top and it's no wonder the cap leaks. Coolant blows off, pressure drops and the coolant boils.

    A 50/50 mix of coolant/water boils at 218 at atmospheric, 265 at 18 psi. A 70/30 mix (max concentration/GM approved BTW) boils at 218 and 276 respectively.

    Put the 18 pound cap back on and leave it there !!! It's no wonder you're having problems - the cooling system IS NOT designed to run at less than 16 psi. Yes there will be some pressure in the system after overnight, and if there is, the head gasket is not blown. Restore the cooling system to design normal and stop trying to outguess the engineers.
    Thanks so much Sub. I think you just saved me hours of grief and a lot of money. The whole problem started with the coolant pipe leak. Then even after it was fixed I would check that black tank every few days and feel the need to have it 3/4 full instead of 1/2. From there the chain of events would compound just as you described.

    My OEM cap says 15psi "add dex-cool only" Therefore its obviously a GM cap. LOL. Should I buy a 16 or 18 and go with the stant lever lock type? I am sure there is a thread on caps if I search for it either way.

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    Re: Is 235 too hot for a N*star on hilly roads?

    "The purge line is SUPPOSED to constantly bleed coolant back to the surge tank: That tank is also connected to the system at the bottom, and the purge line removes air and gasses from the coolant in order to prevent pump cavitation. Stick the purge line somewhere else and you pump all the coolant out !!!"

    Just wanted to clarify that I may of been confusing when I was talking about lines at the black tank. I left the actual purge line that runs along the intake to the black tank (across engine) alone. I get some crazy ideas at times but messing with that would be asking for trouble, HA! The only line I tampered with was the one that would normally be aimed at the ground near the pulleys. Car was allowed to idle about 30 minutes with the 7 psi cap on and the correct amount of coolant. I wanted it to blow off any excess while still at home. Fans cycled in conjunction with A/c and car stayed around 203 tops. VERY HAPPY. Now everything is back to "normal" with the GM 15 psi cap and I am off for a 60 mile local trip! Thanks again Sub, you really saved me a lot of future headaches. Sometimes I OVER THINK and I will admit I never totally understood coolant pressure and boiling points. Wish I had posted on a forum back when I fought with a GM 5.7 Diesel HG a few years ago doing similar stupid things! HA!

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    Re: Is 235 too hot for a N*star on hilly roads?

    Leave the GM stock 15 psi cap on there. Whatever type it is: all these tanks are as different as fish in the sea - mine has a screw on cap set to 18 psi. Others are screw on at 15 or 16 psi. Others are twist-to-lock at 15 psi.

    Use your stock cap or replace it with an identical unit from NAPA.

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    Re: Is 235 too hot for a N*star on hilly roads?

    I will admit I never totally understood coolant pressure and boiling points.
    Very simply put, water boils at 212 at sea level pressure (29.92). Raise the pressure and the boiling temperature rises. Lower it, and it goes down. That is why you pull a vacuum (the opposite of pressure) on the A/C system before charging it. You can actually boil off any moisture in the system at 70 degrees.

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    Unhappy Re: Is 235 too hot for a N*star on hilly roads?

    What a day I had! I dont know what to think now. The car acted perfect for around 45 miles of city and highway driving today. Before seeing the post about leaving my 15 psi cap I stopped at Advance auto and asked them to look up the cap for my car. They came up with 16 and I opted for the Stant lever lock.

    When I opened the hood to change it I noted about 12 ounces of coolant was in my gatorade bottle I keep by the battery. Instead of going in the ground I like to catch the excess coolant plus monitor it. I just assumed I never had the correct level in the tank, I think it has to be actually COLD to know you have it at half based on much appreciated advice I received earlier today.

    ANyway, i installed that cap and 12 or so miles later of city, then highway, then a BIG hill I got all the warnings. A/c off, Idle engine...then STOP. I immediately did of course and let it cool awhile. I KNOW this is dangerous but I was able to get enough pressure released to get the cap off while it was still in the 230's. I started it back up and filled it again with mostly water. At this point I just wanted to get it home and deal with it the next day totally cold. Well, going back down that big hill it shot right back up to the 250's again. I stopped at some relatives house and let it cool at least half and hour and filled it again and it pegged in only minutes, once again.

    I began another cool down, fill up but this time it wasnt going to cool down. It went from 229 to IDLE ENGINE just like that. SOmething told me check the T*stat but when I got the bottom hose off (still hot while engine ran and I was spraying water on my hand) coolant did come out. Then with engine running I had a helper spraying water in tank while I undid top hose. After a pause water came out there and to make a long story short, the car dropped down immediately and ran home on mostly water at 197 as usual.

    My grandpa keeps saying take back the new T*stat for an exchange and then drive the rest of the summer without one at all. I just dont think this car would appreciate that. If I buy the stud bolt kit and tear this down I will be so mad at myself if I find there was no problem. Anyone who doesnt know N*star says noway that car has blown a HG but we all know better, hA!

    The car is worthless the way it is (black base 99 deville with 110k) and I know if it was fixed right it would be a great car with many more years left in it. So frustrated right now. Thinking about just yanking the plates before I make things any worse, LOL.

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    Re: Is 235 too hot for a N*star on hilly roads?

    That does not sound good. Get the block test kit from Napa and test the coolant for the presence of exhaust gases. And DO NOT heed gramp's advice, no mater how well intended. You NEVER drive a car without a radiator cap. You won't be any better off than you are now and won't get more than a few miles.

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    Re: Is 235 too hot for a N*star on hilly roads?

    Quote Originally Posted by DanDeville99 View Post
    If I buy the stud bolt kit and tear this down I will be so mad at myself if I find there was no problem.
    Unless you find a brand new set of head gaskets in there and perfect threads in the block, you won't be mad at yourself.

    Do a leakdown test on the cooling system. Pressurize the whole system to 15 PSI and see if the pressure drops off. If it holds it, you're good. If it loses it, well, time to find the leak. All it takes is a pinhole leak somewhere, enough to let some pressure escape, to lower the boiling point of the coolant mix.

    235 degrees is the highest you will ever want to see a Northstar go. Give it 240 for sensor variance. Any higher then something's screwed.

    I know everyone looks at the Northstar HG job like "holy crap this looks like a big messy job". The good news is, it's not as bad as you think. Change the head gaskets and install studs and your problems will get much smaller. Any cooling system problems after that are easy to take care of (rad, water pump, t-stat, hoses, heater core, etc.).

    I see it this way: If nothing small seems to be causing the trouble, before replacing what doesn't seem necessary, get the HG's done. At very worst, you have gotten some important preventative maintenance done and over with.

    I have a customer from Toronto who's stuck in Boston, MA right now with his Caddy. There's a shop in Boston who'll be installing the studs because he can't make it home- HG's blew on his vacation.

    Better and cheaper to get it done before you go on a long trip. This saves headaches, towing charges, and possibly not finding anyone on short notice to do the job.

    If you decide not to get them done right aways, I wish you the best, hopefully it's just a small issue that has been overlooked, but from what you're telling us, I'd be leaning toward the HGs. One good overheating on an old Northstar will pull the bolts that were holding by a thread.


    Need parts for your Northstar Engine? www.northstarperformance.com

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    Re: Is 235 too hot for a N*star on hilly roads?

    Ranger is absolutely right. Some of my customers have done this too- but running without the cap tight will cause boilover pre-maturely. You'll lose your coolant and there won't be anything left to cool the engine.


    Need parts for your Northstar Engine? www.northstarperformance.com

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    Re: Is 235 too hot for a N*star on hilly roads?

    Heres something a guy in my town did on his Deville when the HG started to go. He got a house hot water radiator vent can. Its a brass can about the size of a medicine bottle with a 1/8" NPT fitting on one end and a vent cap on the other, there is a float inside it that is designed to purge air from your baseboard radiators in your house He put that on a "T" fitting with two hose barbs and installed it in the purge line near the water pump fitting. You need to tie wrap it to something so it stays vertical, and it should also be mounted up high, about even with the top of you throttle body so its the high point in the system. It will collect all the "air" coming thru the purge line and vent it off without carrying any of the coolant with it. He figured it would get his car thru another couple of months so he could find a new car to drive, but after he did that he never had another problem with the car for another year. It won't cure a huge HG problem but might help in situation where the HG is just starting to go, and it only costs about 20 bucks for all the peice you need to make it work.

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