GM 3100 head gasket questions

[harofreak00]

Well I finally started working on it today, for the few hours that I can. I ran a compression test expecting to see whether it was the front or rear head gasket. Here is what I came up with.

Cylinder Number:
1: 171
2: 165
3: 164
4: 179
5: 160
6: 161

Thats a 9% difference from highest to lowest. I was expecting to see 1 or 2 of the cylinders have a very low reading. I called my dad to ask for some advice. He said the compression test is not the only determining factor of a bad head gaskets. He said at the shop, they have a device they can screw onto the overflow tank (radiator cap) to see if there are any exhaust gases getting into the coolant. Obviously, I don't have this tester, and I don't plan on paying to have it done.

I then told him about the problems she was having with the car previously. This might be totally unrelated, but I figured I would explain. She called me to tell her her radiator hose blew up. The hose seperated right near the thermostat housing, at the top of the upper radiator hose. I replaced the hose and then did some test driving in the parking lot to get the car up to temp. I watch the gauge and I saw the temp rise all the way to 195*, and then it dropped down as the thermostat opened, and then slowly rose to 195* again. At that point, I considered the car fixed, just a bad hose.

The next day, she called me to say the car drove to work just fine (10 minutes in 40*F whether), but the car overheated on the same trip home (60*F weather). She drove the car until it actually died from being so hot.

Now entertain me with advice. Do you think this could be a thermostat problem? Do you think the fans aren't coming on, causing the overheating? Or do you think the head gaskets are really bad.

I am not sure what shop she brought the car to, to have them tell her the diagnosis. She said it only took them a couple minutes to tell her.

At this point, the only thing I have done to the car was remove the plugs. I would appreciate any and all advice.

*edit* Here are the plugs, if it matters. I was an idiot and forgot to mark what plugs to what cylinder. Whoops. Notice how one of them is completely white?


*edit2* I bench tested the fan, it IS working. That doesn't mean that the PCM is turning the fans on at the correct time though....

[Hans]

dumb question, but is the water pump working?

[harofreak00]

I would assume. I don't know of a way that a water pump can't work, providing the belt is on. They usually just leak when they go bad, and its not leaking.

[harofreak00]

bump? gearheads?

[Bonneville92V688]

Failed LIM gaskets? 3100 LIM gaskets are wafer thin, and fail very easily. I've done 4 3100s that have had the coolant ports of the gaskets completely eaten away. Generally the 3100 head gaskets don't fail unless the car is overheated due to a bad water pump/stuck thermostat, which is the cause of death of most 3100s. Please note that the 3100 water pump is notorious for failing without leaking, by means of the impeller not turning by breaking loose from the shaft. Some do it, some actually can't because some have the impeller as part of the shaft.

[harofreak00]

What should be my next plan of attack? Change out the thermostat, or check the water pump?

[repinS]

Driving at speed should rule out the fan thing? I find that when I'm above ~30-35mph the temp gauge doesn't creep up as it would in traffic since there's enough air passing through the radiator.

If there are exhaust gases getting into the coolant, the gauge should be doing some fluctuation due to the air pockets. How does the oil look? No chocolate milkshake underneath the oil cap? Does the exhaust smell kind of "sweet" as in burning coolant? Any other symptoms similar to an LIM gasket failure? HG / LIM gasket failure can often cause the same problems.

I've spent a lot of time on a Toyota RWD inline-six board where head gasket problems are the norm, and there doesn't seem to be too much evidence to support it here. Can't rule it out completely though.

[J Wikoff]

I know 3400 LIM gaskets can be a problem, and the top end looks the same as that 3100. But even if you get deep into it and find a bad LIM gasket, I suppose that doesn't rule out a head gasket by default.

Take the rad cap off while it's running... then you'll know if the water pump is pumping. Could be messy though.

[harofreak00]

I did notice the exhaust being a little white, but I haven't really looked at it up close, just seeing it in the rear view mirror. There was a very small amount of condensation under the oil cap.

[repinS]

There was a very small amount of condensation under the oil cap.

That could be the short (10 minute) trip thing that the previous owner did.

For the white plugs, I found this:
( http://www.classictruckshop.com/clubs/e ... /plugs.htm )

Incorrect Heat Range

APPEARANCE: The effects of high temperature on a spark plug are indicated by clean white, often blistered insulator. This can also be accompanied by excessive wear of the electrode, and the absence of deposits.

CAUSE: Check for the correct spark plug heat range. A plug which is too hot for the engine can result in overheating. A car operated mostly at high speeds can require a colder plug. Also check ignition timing, cooling system level, fuel mixture and leaking intake manifold.

RECOMMENDATION: If all ignition and engine adjustments are known to be correct, and no other malfunction exists, install spark plugs one heat range colder.

Are those Bosch Plats the right ones for that motor?

[harofreak00]

I'm not sure about the plugs. I'll put new ones in when I put them back in.

The WP looks like a very simple replacement. Maybe I'll try that before the thermostat. The exhaust crossover has to be removed to get at the thermostat housing.

[JBMark33]

I had a Lumina with the 3.1

I had a problem with it overheating back in the day.

It started out as a leaking heater core, and after I replaced that, it was fine for a short period of time, and then it started over heating again. I replaced all the hoses, the T-stat, waterpump, lower intake manifold gaskets, and it simply ended up being a radiator cap. The waterpump shouldn't take you much longer to do than the T-stat on a 3.8. Other than keeping the pulley from spinning while loosening/tightening the bolts on the water pump, it's real easy.

I guess try the cheap and easy things first.

[crash93ssei]

Intake gaskets.

That is what caused the problem anyways. Same thing happens to many of these engines around here. Intake gaskets go bad, run low on coolant, and cause the engine to overheat. When the owner drives the car untill it dies, it becomes a big problem. They have aluminum heads and they warp easily. Once they overheat to the point that they die, the heads are very likely warped and would cause leakage by the head gasket.

Save yourself the headache and suffering. Pull the heads off, have them checked for crackes and warpage. Have them milled down if they are warped.

You know what to do from there

Good news is that it really isn't a whole lot of money to have the heads checked and milled. We had my sisters done in her '01 Malibu 3100 and it was about $250 to have them checked and milled down.

I would, of course, try the easy things first ( radiator cap, thermostat ) but my money is on intake gaskets. I have seen lots of cars with that engine with intake gasket problems. Just as common as on the 3800s in my opinion.

I believe that all in all, gaskets, oil change, having the heads checked / milled, etc... basically getting the car running again, you will have yourself a very nice vehicle that you will still be able to sell for enough money to make it worth your time

[harofreak00]

If the gaskets were bad, wouldn't I see some weird compression numbers though?

IMO, if its going to cost $250, this car is not worth having the heads checked and milled. I'd rather just sell the car with a known "bad engine".

[crash93ssei]

You might see a little more difference in compression then that, but I can't say for 100% sure, it might depend on the severity of the warpage ( if they are warped ). I just know that I have seen quite a few of those engines around here with the same problem and the heads ended up being warped from the owner ignoring the original problem, intake gaskets.

[Jrs3800]

Your compression test is not a 100% factor for what I would call good head gaskets... But those numbers are quite good and it may not have a blown head gasket.. Hard to say..

On the Plugs, Any GM DIS system will not survive... Those should have never been used with the 3100..

Its possible that the Thermostat is not opening all of the way, it could be sticking.. Its worth replacing to see if it corrects the problem..

Do you have a Scan Tool? So you can see what the PCM is seeing as far as temps are concerned?