: Northstar "check coolant level" -- trying to understand basics

06-29-07, 12:55 AM
Northstar engine from '97 Seville STS. Now at ~100K. "Check coolant level" message has appeared twice over the last six months. Both times I added coolant immediately: ~1 quart distilled water & 1 quart orange "dexcool" on both occassions to replenish the level. Had neither any overheating issues nor any hot temp indications on the temp gauge.

The manual for the car indicates that adding some coolant every now and then is normal. Is two quarts total fluid every three months a normal amount to add?

It may be important to note that the head gaskets were replaced by a Cadi dealership at 75K (before I owned the car).

What are the basic things to look for to try and find a coolant leak? (I've read some other threads, but they seem too detailed and specific -- I'm just looking for general guidelines to start).

Is it worthwhile to replace the water pump for example -- even if it's just preventative? (Isn't the pump a $40 part online?) I'd do it if it's worthwhile, because I've been frightened by all the coolant-problems-lead-to-head-gasket-failure themes I've seen on this forum, but on the other hand I don't want to risk messing something up for an unnecesary repair. Where else should I scan for coolant leaks?

06-29-07, 03:33 AM
Thats a very minimal leak but if your concerned get 3-5 bars leaks tabs and put them in thats the supplement your manual talks about you can also use the powder. but either way its a sealed system just like any other car it's not supposed to leak. the bars leaks should stop it, pull the upper hose and put in the sealing tabs to see if the leak stops.

06-29-07, 09:18 AM
A modern automotive cooling system is a (theoretically) sealed circuit which should never lose fluid under normal operating conditions. Actually, a half gallon of fluid over 2 or 3 months is quite a bit of loss. Do an extensive cold engine search for a small drip or wet spot. If no joy, try the GM/Bar's tablets. (....and only the tablets- nothing else). I have not added 1 drop of coolant to either my STS or F150 in a year and a half, and that's after 75% highway service.

06-29-07, 04:41 PM
I agree with Submariner. That is not normal. There is a leak somewhere. When the coolant level light illuminated on my '97, I could not find a leak. Finally I searched with the engine running and found a hairline crack at the base of the nipple on the surge tank that the purge line attaches to. It was so small it was not visible unless the coolant was flowing and seeping through it. Sometimes the surge tanks will develop a crack on the bottom where it is not visible or a side tank will develop a small that will evaporate before it becomes visible. Water pump cover gaskets are also a known leak spot. Use an inspection mirror to check the water pump shaft seal for a leak, but don't change it unless it is leaking. Dried Dex will leave a whitish residue as a telltale sign. If none of this helps, get the cooling system pressurized and let it set. Eventually the leak will show itself.

06-29-07, 09:58 PM
OK fellas thank you all for the info. I intend to start looking for leaks over the weekend.

07-12-07, 12:23 AM
I looked around and I hope I found the leak: there was orange sludge around both ends of the top radiator hose.

I replaced the hose and took the opportunity to flush the coolant.

Maybe this should be a new topic, but here's a brain teaser:

After the system is drained after the final flush, how much DEXCOOL vesus distilled needs to be added to get a 50/50 mix in this sytem?

I was surprised to learn during the flush that the cooling system cannot be fully drained. Thus adding 50/50 on the final fill does not yield 50/50 in the system.

On the final fill I added more DEXCOOL than distilled (~4 Q DEXCOOL & ~2.5-3 Q distilled) to account for remaining distilled in the system. If the system holds more than 8 quarts though then I'm lean on DEXCOOL. To be safe I intend to take the car to a garage to test the DEX/Water ratio (they said they can test the ratio for free).

Also, I crushed three tabs and put them in the upper radiator hose because the lower hose was hard to remove, so I figured the lower hose was well sealed and that I'd leave it alone. Are tabs in the upper radiator hose OK?

07-12-07, 08:46 PM
If there was a 50/50 mix in there and you added a 50/50 mix you would still have a 50/50 mix. That is why we always say, pre mix it before installing. The only way to tell what you have now is to use a refractometer.

Tabs in the upper hose are fine.

07-13-07, 10:09 PM

I was searching posts on transmission flush when I happened upon the "don't flush w/ distilled, can't drain everything" stuff for coolant. This weekend I'm going to partially drain and then refill with 60/40 in hopes of getting close to 50/50. Afterwards I'll test with a refractometer too.

Thanks for all the great info. This forum has been very helpful to me and I appreciate it.