98 Lumina Blown Head Gasket?

[sting8282bird]

If you replaced the front head gasket, there is not a lot more to replace the back. When I replaced mine, I knew that there was a leak at the lower intake manifold. I decided to do both head gaskets because I was already there. I'm glad I did that because the passages were caked shut with dexcool sludge and maybe some stop leak. When I asked how much it would cost, I was told ~$1000. If I ever have the problem again, I will probably end up paying someone to do it so I can get my car back quickly... (it took me 4 weekends in 35 degree raining weather conditions partially under a carport).

[w_nter]

@sting8282bird

I was having a lot of the same issue that you fixed. Disappearing coolant (no puddles), over heating after long stops, wild over heating while driving (inconsistent figured out it was air pockets reentering system). I also saw the price tag of a LIM gasket fix and had the response of "Nope, I'll do it myself." P0401 code was also popping up before hand. Cleaned out plenum and passage when I did T-stat a few weeks ago - now gone.

Actually just wrapped up the LIM last night, and verifying today that I got all the air out of the coolant shystem. Like you though, I don't believe my fans are coming on during the long stop lights or 5 o'clock traffic. ECT Sensor is new, t-stat is new, checked fuses, checked all three relays - haven't flat out replaced them - all checked out fine (audible click when car started). What else were you checking when you found your fan problem? I've possibly missed something I know.

Also did new spark plugs and wires - first time troubleshooting new plugs - never had an issue pop up afterwards, but getting a little bit of a rough idle. Feels like that "misfire lope" and noticed the front plugs were more challenging to get the right installation depth - I mention this bc wondering if overheating could have caused any warpage or seizing. I've seen other threads mention that before.


Thanks in advance.

[sting8282bird]

w_nter,

I found the fan problem when I was trouble-shooting the overheating. I checked all the items you noted below, fuses, relays, temp sensor and found no problems.

The three projects I had were 1)head gasket/LIM gasket, 2)P0401 code and 3)Fan operation.

I decided to fix #1 and #2 and then try and figure out #3 when the car was drivable. After the fix, the temps have not gotten above ~halfway on the temperature gauge, so until now, I forgot about it. I will say that from recollection that the temp gauge only gets to halfway while idling for a period of time (fast food drivethrough). Either the fan is now operating, or I'm getting enough cooling by radiation. I might check into this this weekend. If I find something, I'll let you know.

[kevinb70]

the fan wont cut on until 230 degrees with OEM coolant temp switch. for me, thats way too high. if the fan cut on at an earlier temp, or when speed < 15mph to be more proactive, rather than reactive to an already high temp. i am still using the 195 degree tstat and want to go 185/190 when i flush my coolant next time. coolant temp switch is a 3/8" x 18 thread

[w_nter]

Originally Posted by sting8282bird

w_nter,

I found the fan problem when I was trouble-shooting the overheating. I checked all the items you noted below, fuses, relays, temp sensor and found no problems.

The three projects I had were 1)head gasket/LIM gasket, 2)P0401 code and 3)Fan operation.

I decided to fix #1 and #2 and then try and figure out #3 when the car was drivable. After the fix, the temps have not gotten above ~halfway on the temperature gauge, so until now, I forgot about it. I will say that from recollection that the temp gauge only gets to halfway while idling for a period of time (fast food drivethrough). Either the fan is now operating, or I'm getting enough cooling by radiation. I might check into this this weekend. If I find something, I'll let you know.

That's basically exactly what I had. We had 5 o'clock traffic yesterday and after being stuck in that, the temp got past the 3/4 mark - I may just have more air in the system to get out. I'm going to mess with that tonight. I've seen that this model can be a pain with air from time to time.

Ya, let me know what you do with the rad fans - nothing is checking out wrong, but long stop lights or stop and go traffic are seem to be the only effector right now. Thank god! That LIMG took care of a lot.

Originally Posted by kevinb70

the fan wont cut on until 230 degrees with OEM coolant temp switch. for me, thats way too high. if the fan cut on at an earlier temp, or when speed < 15mph to be more proactive, rather than reactive to an already high temp. i am still using the 195 degree tstat and want to go 185/190 when i flush my coolant next time. coolant temp switch is a 3/8" x 18 thread

I still haven't noticed a particular temperature causing my fans to come on or not. That's why I've been looking into all this. The fans run fun on AC but don't seem to run during long idle periods. I've already seen posts advising to stay away from the lower temp T-Stats. Can't remember their exact explanation but it was a point made a couple of times. SO the Switch is located where? are you referring to the ECT? I've replaced the ECT Sensor right behind the T-stat. Which/location SWITCH are you talking about?

[kevinb70]

we are talking the same temp switch/sensor. there are 2 circuits in the sensor, one drives the dash temp gauge, the other feeds into the PCM where the computer decides when to turn on the electric fans.

The fans never turn on - that's exactly the problem. Chevy engineered it to where the fans come on at 230 degrees.... that's way too high for my comfort. My fans to my knowledge have never come on due to the temp getting to high. Only by turning on the A/C. The tstat is 195, the PCM turns on the fans when the ECT reads 230, that's 35 degrees above normal operating temperature. I think that is just bad design. I would rather have some wear an tear on the fans than my engine running that hot.

wouldnt rely on the dash gauge, hopefully you have an infrared temp gauge like I do and can measure the temp at the t-stat more accurately than the gauge. I think the gauge would pretty much have to be pegged out to the right before the dam fans come on. Or an ODBII scantool to pull the temp from the computer which is more accurate.

If you are overly concerned, I'd tap into the a/c signal that turns on the fan relays and have a manual switch to turn on the fans in rush hour if you didnt run the a/c. In rush hour, i have turned on the a/c just to keep the fans running and keep the temp down. I wouldn't do this unless you used a diode because your switch could trigger the A/C clutch accidently... just a bad idea.


a better way is to break the signal wire between the PCM and fan relay coil:

in my diagram, I assume the PCM delivers +V and the other end of the relay coil is grounded... of course this may be backwards, with one coil contact is always +V and the PCM delivers a ground signal to the other end of the coil.

you can add your own switch and SPDT relay. your switch can power the relay coil on the new relay.



Note: you are tapping into the fan relay COIL, not the Common/Normally open contacts

i dont know if the PCM supplies +12V +5V or ground to trigger the stock fan relay, if you want to do this then youll need to see what the signal is. you match this signal to the NormallyOpen contact on your new relay.

when you turn on the switch your new relay activates, bypassing the PCM signal (which NEVER operates when you want it to) and you send +12V/+5V ground signal from the normally open contact to the common contact and this signal turns on the fan relay. you gotta cut the wire from the PCM to the fan relay in the fuse block and wire the PCM signal to the Normally Closed contact on your new relay and the other end of the cut wire to the Common contact on your relay. The Normally Open contact has a constant +12V/+5V/ground (to duplicate the same signal the PCM delivers)

the effect is, when your switch is off, the fan relay is controlled by the PCM. when the switch is on, YOU control the fan relay.