Hi Guys,

I am having trouble determining if I have blown head gaskets or a leaking radiator on my 96' deville (120k miles). For the past two/three months I have been having to constantly refill my coolant. Whenever I drive for a while and bring my car to a rest (motor still running) I notice that the radiaor is leaking a bit. I just had my oil changed and tried to get a pressure test, but the tech said that it was impossible because it was an internal leak somewhere. I took my car to another service station and the guy mentioned that I only had a leaking radiator, w/o performing any kind of pressure tests. The only thing this guy did was removed my oil cap and fingered around to see if coolant was mixing with my oil. For the last couple of weeks, I have been putting in regular H20 in the radiator to see if the water was definitely mixing in with the oil, but it doesn't look so. As far as performance, the car drives with no noticeable problems and it doesn't make any knocking noises when I drive, even at accelerating speeds. I am thinking about replacing the radiator this weekend. Any advice before I do so??? Thanks in advance.

P/S: Any directions or where can I find how to clean/replace my EGR valves myself.

Hi Guys,

I am having trouble determining if I have blown head gaskets or a leaking radiator on my 96' deville (120k miles). For the past two/three months I have been having to constantly refill my coolant. Whenever I drive for a while and bring my car to a rest (motor still running) I notice that the radiaor is leaking a bit. I just had my oil changed and tried to get a pressure test, but the tech said that it was impossible because it was an internal leak somewhere. I took my car to another service station and the guy mentioned that I only had a leaking radiator, w/o performing any kind of pressure tests. The only thing this guy did was removed my oil cap and fingered around to see if coolant was mixing with my oil. For the last couple of weeks, I have been putting in regular H20 in the radiator to see if the water was definitely mixing in with the oil, but it doesn't look so. As far as performance, the car drives with no noticeable problems and it doesn't make any knocking noises when I drive, even at accelerating speeds. I am thinking about replacing the radiator this weekend. Any advice before I do so??? Thanks in advance.

P/S: Any directions or where can I find how to clean/replace my EGR valves myself.

Is it over heating under load. Climbing hills etc.

I am not a mechanic, but if the coolant is leaking into the heads, then the pistons will be compressing liquid instead of gas - and they don't like to do that. 10:1 gas compression is one thing, 10:1 liquid compression is a lot different. Based on that, I don't think it's leaking into the heads. I guess you can always pull the plugs and crank the engine - see if any coolant comes out.

Hi Guys,

I am having trouble determining if I have blown head gaskets or a leaking radiator on my 96' deville (120k miles). For the past two/three months I have been having to constantly refill my coolant. Whenever I drive for a while and bring my car to a rest (motor still running) I notice that the radiaor is leaking a bit.


P/S: Any directions or where can I find how to clean/replace my EGR valves myself.

I think you answered your own question. Probably a leaking side tank. They are plastic and known to crack. Also, if you are adding plain water, you are diluting the 50/50 mixture which can cause overheating.

Go to the Tech Tips section, There is a post on how to clean the EGR. It is easier if the fuel rail recall has not yet been done as there is a little flex in the plastic fuel lines. The stainless steel lines do not flex and need to be removed.

There are TONS of threads on this.

The radiator is fairly easy to pull and check. Once you pull the large decorative shield you can see a lot of it without even pulling it. Radiators are not too expensive on the internet.

Northstars do not put coolant in the oil until the head gasket is extremely bad. The guy who only checked under the oil cap is not much of a mechanic.

Check your radiator, water pump, and crossover areas for leaks. Refill with 50/50 coolant. Have a radiator shop do a combustion byproduct test after you drive it a few days if you did not find a leak. Since you said you see coolant you will probably find a leak though.

If it was HG you usually lose coolant without seeing any leakage. No coolant in the oil. Initially it would still run well and get good gas mileage. They can be tricky to diagnose.

Never overheated nor do I see any thick white smoke, except the usual fog from the early morning startups. No leak in the side tank either nor water pump. I am getting a "service emissions system" message though. I presume this is from using regular unleaded and maybe the EGR valve needs replacement or cleaning. I will pull codes this afternoon. Is it possible to perform pressure tests or a combustion byproduct test, with a radiator leak? Was told that it wasn't. BTW, what is a combustion byproduct test???

Using regular gas will not set the service emissions system message. Pulling the codes will tell you what did.

A bad head gasket will not cause billowing clouds of steam til it is really bad.

Combustion byproduct test is testing the coolant for the pressence of combustion gasses.

You can buy a pressure tester from an autoparts store for $100 or maybe even rent one from a tools rental place.

I had a leak problem with my cooling system on my 1985 Deville some time ago. I took it to a garage and they just pulled out this thing that replaces the radiator cap. It has a pump handle on it. They pumped it up to 14 psi and watched for leaks. Took all of 20 seconds to find the leak. Didn't even have to warm the engine up.

http://www.jcwhitney.com/autoparts/ItemBrowse/c-10101/s-10101/p-100000166905/mediaCode-ZX/appId-100000166905/Pr-p_CATENTRY_ID:100000166905

There has to be numerous benefits to installing a brand new radiator in a ten
year old car.

I purchased one off the internet/Ebay

Repairing one side tank at a radiator repair just doen't cost effective any more.

You automatically get a new tranny cooler in the new radiator albeit barely enough capacity. I think that is the case, could be wrong though.

Hope you drive that N* for many more miles.

Just pulled my Codes

AC1312 Current
TCO083 Current

I looked in the code listing but I can find out what these means, any ideas?

Found a radiator from Bumper to Bumper auto parts for ($175.00 w/ 1yr warranty), would it be necessary to add the BarSeal pellets even with a new radiator.

B1312 - High Side Temp Sensor Open Circuit (it's refering to the A/C system)

I can't find TC0083, but in the OBDI list T083 is low brake fluid. You might check that.

My 96 deville does the same thing. I can see the steam in the winter and smell the coolant. But there is none on the floor. I will do the pressure test this weekend and see what I come up with. Mine is on the driver side somewhere. (keep me updated).

Well I did the test last night and it looks like it is going to be a manifold intake gasket leak. I pumped the pump up to 15 pounds and there was not a drop to be found. I looked under the rocker cover cover and found residual coolant and that has to be the case. Everytime I start the car up and get the motor hot it evaporates off of the top of the head. I don't know how hard it is to change but if someone could chime in that would be wonderfull.
Thanks...

The Northstar intake manifold is a dry intake. There is no coolant running through it.

I'm no car expert but I have a 95 SLS that's been having the same problem. My mechanic did a pressure test and found no leaks present. Thus, his conclusion was:

1) Wrong cap (is this the radiator cap) on the coolant recovery tank (wherever you pour the coolant into). Not having the right cap screws up the pressure and causes overheating, which then bubbles the coolant to the top of the tank where it exits through a little hose. I have the wrong cap and need to replace it.

If the cap isn't the problem, then it's one of two things.

2) Radiator has problems and might need to be replaced. If the radiator gets fixed and the problem persists, then it's:

3) Head Gasket is blown.

Let's hope it's a cap issue.

Let me know if and how you rectify your situation. Best of luck.