99 Deville Northstar Overheat

[llaramie]

I ask him if he can prove it is a head-gasket issue, as i see no water in the oil dip stick; I see no goop on the oil cap that would of indicated water contamination.

Neither of those conditions will be present on a Northstar when the HG fails.

Now the car seems to be running fine; but i see that it runs in normal easy traffic between 197F and 222F; generally around 203 to 208 in slower traffic. Is this okay?

Yes.

Will it run hotter in summer weather?

Probably. It will get worse.

If the issue was the purge line, that somehow is now clear, do the hydrocarbons that my last mechanic noticed necessarily mean it is head-gasket time?

Yes.

You can borrow a block test kit from Autozone and just pay for the test fluid and run the test for yourself if you want to.

I have been running cool, 196 to 203, since my last mechanic cleared purge line and found hydrocarbons in coolant--that was 10 days ago.

Also, every day as i get out to start the car for the first time in the morning, I go and check the coolant-cap releasing any pressure and checking the coolant level.

I have been driving about 20 miles a day, running my same errands (breakfast, gym, shopping, etc)

I did have some pressure buildup last week, but for the past three mornings I find no pressure build up at all.

I thought any hydrocarbons would have caused a buildup in the surge tank?

I have not driven this car on the expressway for the past 10 days -- I think I will do that tomorrow --70 mph to see if i build up any hydrocarbons.

[Ranger]

Low coolant temps and no pressure in the surge tank do no point to a bad HG. Might want to do that test again.

[KHE]

I have been running cool, 196 to 203, since my last mechanic cleared purge line and found hydrocarbons in coolant--that was 10 days ago.

Also, every day as i get out to start the car for the first time in the morning, I go and check the coolant-cap releasing any pressure and checking the coolant level.

I have been driving about 20 miles a day, running my same errands (breakfast, gym, shopping, etc)

I did have some pressure buildup last week, but for the past three mornings I find no pressure build up at all.

I thought any hydrocarbons would have caused a buildup in the surge tank?

I have not driven this car on the expressway for the past 10 days -- I think I will do that tomorrow --70 mph to see if i build up any hydrocarbons.

Your coolant temps sound normal. If it was heating up due to a blocked purge line and the line is now clear, I would not tear into the engine.