99 4.3 Rough Idle, Low Temp, Bad Gas Mileage

[ericn1300]

An air leak or coolant leak into #4 cylinder is most likely the problem of your mis-fire and the under temp condition. The mis-fire, and lack of combustion, combined with the cooler contaminant (air or coolant) will cause the engine to run cooler than normal.

I know a lot of people here are going to say NO but a tube of Aluma Seal radiator stop leak might just fix your problem.

[dr_lee29]

So do you think that air/coolant leak is a result of a blown head gasket or another seal?
Several years ago, I dealt with the Dex-cool demons and the truck overheated a few times. One time it got pretty hot (I wasn't driving it at this time). So I've wondered about the heads/head gaskets but I haven't had it hot in over 2 years and this is the first time I've had a problem with the truck that wasn't a quick fix.

[ericn1300]

iron to iron on the heads and block, an overtemp would more likely warp the intake. new gaskets won't overcome a warped componet, did you get everything machined?

Originally Posted by dr_lee29

this is the first time I've had a problem with the truck that wasn't a quick fix.

After 7 pages of posts and suggestions do you really think some one is going to come up with a quick fix now? MT-2500, you are nominated for sainthood.

[tempfixit]

IF you feel like using a sealant for possible head gasket leak BAR"S LEAK has a newer product you may want to check out called Block Seal Head Gasket Fix. Expensive. I am going to try it on a engine that I think has a blown head gasket, if it works great and not will be a lesson learned.

[dr_lee29]

No need to make me feel stupid over the thing. I don't expect any one to give me anything. I'm not looking for handouts, I just thought maybe someone else has had this problem before and might say it sounds like this. I really appreciate all the help, sorry if I'm being a pain to work with, the easy thing to do is just ignore me, no need to nominate folks for sainthood.
I'm also not looking for an easy fix, even before 7 pages of posts. I was trying to say that the truck has been pretty easy to care for and easy to diagnose up until this point. I also meant that if the overheat caused a problem, I expected that problem to show up soon after the overheat occurred (2 years ago). But maybe it takes a while for something like this to show up, I don't know thats why I asked.
The answer to your question is "no" I did not machine the intake or the block when I replaced the gaskets, looking back maybe I should have.
Look if I find the answer to the problem I'll be sure to post back here. Again, sorry about the mess. I don't want to be a pain. Thanks for the help.

[ericn1300]

Didn't mean to belittle you or your problems, and I do apologize for anything offensive I may have said. Please do keep us informed. The compression check is really important at this point since Your problem is deeper than you thought.

[coreweave]

dr_lee29,

I feel your pain. I had an older Mazda that had similar issues with the engine running "cool" along with no heat. I replaced a quite a few parts myself without success. I lost patience so I took it to a mechanic to have it looked at and they flushed out the entire system, which I have done several times. Surprisingly, they fixed it. Coolant temp was back up to 180deg (per Mazda) and I had heat!

A few weeks later, my water pump went out and so I had to drain the entire system. After filling it back up with coolant, the symptoms came back! I believe that there was air trapped in the system which caused problems. I "burped" the system by taking the radiator cap off, and holding the rpms to 2k rpms without any success. I don't know if there is a better way to burp the system but that's what I've been told. I never did get it fixed before I sold the car. Might be worth a shot to try to burp the system.

As for your fuel pressure issue, have you inspected the vacuum line leading to the fuel pressure regulator for cracks and make sure it's on securely?

If you think you may have a head gasket problem, have you popped the radiator cap off with the engine running (cold engine!) and looked for any bubbling? How about pulling the cyl #4 plug and inspecting the porcelain for a white color? If yes, it may buy you some time until you can get it fixed by re-torquing the head bolts.

[pageman1]

I have a 1996 blazer that has one of the same problems as yours ,in that it never comes up to full operating [165 degrees or so] temperature ,and also gets really crappy fuel mileage in the 10 mpg range.i also changed many things ,such as 2 thermastats , checked the egr valve ,and a million other things.the only thing that was suggested to me that i haven,t done yet was to get a new fan clutch.seems to be fine to me,but i am getting really frustrated with this pos.it used to get much better fuel mileage.i don,t know if you ever solved your problem ,but if you did ,i would be very interested to learn what was causing it to run so cool. Thanks

[j cAT]

Originally Posted by pageman1

I have a 1996 blazer that has one of the same problems as yours ,in that it never comes up to full operating [165 degrees or so] temperature ,and also gets really crappy fuel mileage in the 10 mpg range.i also changed many things ,such as 2 thermastats , checked the egr valve ,and a million other things.the only thing that was suggested to me that i haven,t done yet was to get a new fan clutch.seems to be fine to me,but i am getting really frustrated with this pos.it used to get much better fuel mileage.i don,t know if you ever solved your problem ,but if you did ,i would be very interested to learn what was causing it to run so cool. Thanks

wrong or not installed properly T stat...........