2003 Blazer. Noticed a few months ago that I had lost a decent amount of coolant, plus had a noticeable coolant smell outside the vehicle. And white smoke from exhaust, especially at startup. So I was starting to think that I had a bad head gasket. A year ago the radiator ruptured and needed to be replaced. I wasn't driving it at the time so I have no idea how badly it overheated.

So I bought a coolant pressure tester to see what happens. After several minutes, pressure only dropped about 1 PSI, and with the truck running the pressure builds slowly. According to the tester instructions if the head gasket was bad the pressure would build quickly. Plus the fact that I have no milkshake on oil cap or dipstick and the oil seemed normal when I changed it last week. So now I'm not sure. Didn't see any leaks, but I didn't remove any components so it could've been hidden (will be doing a closer look this wknd)

And then the other day I get a SES light for a P1028 (coolant not getting hot enough) From what I've read air in the system could cause this code to set, and there's definitely air in there, the heater core is noisy as hell. I was actually wondering if the heater core could be the problem, because I've lost heat a couple times and it was noisy even before the radiator went out. Only problem is that there's no evidence the HC is leaking. No wet carpet. Don't want to tear into that dash for nothing.

So should I concentrate on finding the leak first before testing the sensor/thermostat?

LIM gaskets were replaced four years ago by a shop, could they have failed? Would I be getting the same symptoms for a LIM gasket leak/head gasket? Best way to confirm? Thanks

edit: the white smoke could be because I park the truck in my detached garage, and it gets very moist in there. Also very cold temperatures around here lately.

 

What is the condition of your hoses? Could you have a leak in them?

 

Been kind of busy, haven't had much time to work on this. I did try spraying brake clean around the intake manifold while the truck was running to see if there was a big leak there, but no change in engine speed. Been keeping an eye on the oil, so far it still looks normal. Definitely noticed a coolant smell tonight when I first started it, still a lot of noise coming from the heater core.

Upper and Lower hoses are new, as for the others I did a visual inspection while the system was under pressure and didn't notice any leaks.

 

Still dealing with this, hoping for some guidance. I definitely feel that my P0128 code and the coolant loss/smell are related, but not sure how/why. Just to rule it out I bought a new Stant 195 degree thermostat, also checked the ECT sensor. After putting in the new 'stat the truck still won't go above 182 degrees (maximum temp usually after a heat soak or stopped at a stop light, otherwise while cruising down the highway at 75 MPH the temp stays at 172-174. As for the sensor I checked the voltages at the connector and they were good, and with the truck sitting overnight the IAT sensor was 44, ECT was 46 and ambient air temp was 47, so that seems normal. Also when observing the ECT temp with a scan tool while driving there aren't any abnormal fluctuations.

So I think I need to concentrate on where the heck the coolant is leaking from. Hooked up the pressure tester again, this time after a half hour the pressure dropped maybe 1/2 PSI, if that. So the leak is very small.

What would be the quickest/easiest ways to rule out LIM gaskets? I am fairly confident that it's not the head gasket like I said in my previous post. I did have the LIM gaskets changed a few years ago by a shop but maybe they did a crappy job. Like I said earlier I did seem to have a lot of white smoke coming from the exhaust, but it goes away after awhile. Oil still seems normal, smells okay and looks okay. Engine noise seems to be lower in tone, but maybe that's my imagination.

Best way to rule out the heater core?

This is really frustrating me to say the least.

 

You don't say whether or not you burped the air out of the system. If not, this could be causing your P0128. Burp it by raising the front end of the truck (car ramps work well), remove the radiator cap (cool). Idle the truck, heater on full blast and add coolant as needed through a couple rotations of the thermostat opening (maybe a few).

As far as the leak and smell, I worked on a Blazer that had a tiny leak at the very back corner of the LIM gasket. You couldn't see it easily and it would weep coolant onto the back of the engine and dry almost instantly with only the smallest hint of a whisp smoke I couldn't see until I got a mirror back there. On the other hand that would probably not cause the white smoke out of the exhaust you're experiencing. I'd suggest after a overnight cold soak you stand at the exhaust and have someone else start the truck. You should be able to easily smell if it is coolant or not.

 

I did burp the system after replacing the thermostat, but after a while air seemed to get back in the system because I started hearing a lot of noise coming from the heater core again. The P0128 appeared after I noticed the coolant loss, and I hadn't opened the system yet. I had cleared the code after replacing the stat but after a few trips it popped back up.

I really hope I'm not damaging the engine by driving it (if the coolant is getting into the combustion chamber) but the oil seems okay so I'm taking the chance.

As for the smoke from the exhaust, I have put my nose right up to the tailpipe and it doesn't really smell like anything, but there IS a coolant smell coming from somewhere. I think I have an exhaust leak somewhere along the pipe under the truck, condensation immediately starts dripping around where the cat is and the smoke comes out from under the truck as well. Maybe this is causing more condensation to form? Like I said earlier the smoke goes away after the truck warms up.

I'm thinking of leaving the pressure tester on the truck overnight with a piece of white paperboard under there to see if anything shows up.

If it wasn't still cold here I'd bypass the heater core and see if the coolant loss stops.

 

I think I recall a situation in a recent thread where it was discovered that there was a pin-hole in one of the coolant hoses. I forget how it was found but it might have been by using a coolant system pressure tester with the engine cold (not running) so that no coolant would evaporate and the leak would be easier to find.

 

Yeah that's what I've been doing, so far no luck. Like I said above I'm going to leave it overnight with it pressurized, see if I can spot it. The upper/lower/bypass hoses are new, of course that doesn't mean they're good.

I'm waiting for the truck to cool down a bit an then I'm going to go back out to the garage and install the pressure tester.

edit: just checked on it, system lost about half the pressure in six hours. Is the system supposed to hold pressure indefinitely? If not then I think I have an internal leak, because there were no wet spots under the truck. I figure with that amount of pressure loss there would be some evidence on the ground. Wonder why it's not showing up in the oil.

 

I'm about to just say f-it and say there's an internal LIM leak. I just hate to go through the trouble of tearing apart the LIM when it was just done a few years ago without some type of confirmation.

What kind of test can I do to prove that there is an internal leak?

 

I totally feel for you. I'd much rather have a positive indication that a part or system is bad before replacing it rather than just going by a process of elimination, especially for a complex fix like the LIM gasket.

I would think that if there was an LIM gasket leak it might show up when the engine was cold if the coolant system was pressurized. I'd look for coolant in the oil.

However, you did have the LIM gaskets changed. Even if they were not the upgraded ones, you'd think they'd last for at least several years before failing. With that in mind, I'd expect your problems to not be the LIM gaskets.

My suggested test is the result of my brainstorming.

If you did have to replace the head gasket, you'd have to install new LIM gaskets anyway.