Bogs down when turning on heat
 

I think I have this figured out, I just wanted to comfirm this
So, I have the bad valve stem seals, smokes on start up, So I put 10w30 oil in there so its a bit thicker so it does not get past the seals as easy, since I put in the 10w30,
I noticed when the truck is cold, and I turn on the heat, it bogs down quite a bit for a second and the lights dim like crazy, but then it recovers.
Am I correct to assume this is because of the thicker oil in the cold air, in combination to turning on the heat, since it kicks on the AC compressor taking more torque from the engine?

When it does this, that is all that happens. No check engine light, nothing, So I am assuming that its from the thicker oil (I live in minnesota)

It does not do it when it is hot, Just cold.

mine dose the same thing when cold

and i got winter oil in there

Ok, just making sure it was not a bigger problem, It must be that AC compressor kicking on.
I did not notice it until I put in the 10w30, When I had the 5w30 it seemed to not do it, or if it did, it was not nearly as bad.
Maybe I will just start to wait for it to run a bit longer before throwing on the heat from now on.
I think I may be regretting the decision to put in the 10w30 however, Sofar we have been spoiled with the temps here in MN being suprisingly warm, and there being little to no snow. I feel like this "dream" will all come to an end soon and its going to get cold as heck. Oh how I need a garage!

Hope everyone's newyear was good and safe!

Your heat doesn't engage the AC compressor. Defrost does, but not heat. Also, it would help if you put your vehicle information in your signature or in your garage so we know what you're driving (outside of being a 1st Gen) without having to search for it.

What setting do you have your fan on when you start the heat? Dimming lights is usually a sign of a weak charging system when a load is placed on it. How's your battery? Cold (as well as extreme heat) really gives car batteries a rough time. Alternator good? All connections and grounds clean and dry with no corrosion or rust?

I just have a hard time contributing dimming lights with a heavier weight oil.

Battery is less than a year old, Alt I am not sure, I will have to go through the previous owners recipts to see when that was last replaced, Checked the positive and negative on the battery and they are corrosion free as well as the Alt.
It is defrost that I turn it on, I should have been more specific when stating that in my first post, since I am aware that the AC compressor only turns on with the def.
I have the fan on low when I turn on the heat and then switch it to high.

It Only does it when it is cold.
It bogs down enough to dim the headlights and the interior lights, but not enough for me to have to hit the gas to keep it running, it recovers within less than a second.
Truck is a 1993 GMC Jimmy S15 SLT with the 4.3L
I will add the info to my sig.

Ok that makes more sense now. Check all your pulleys for increased drag. Your compressor may be in the beginning stages of seizing as well if it's pulling that much power from the engine. Does the compressor make any noise when it's off, or when it's cycling?

You may also want to look into upgrading the "big 3" to decrease voltage drops with large draw accessories such as defrost. A quick search should give you several threads on what it is and how to do it if you're not familiar.

Another possibilty is a dirty IAC which will make it sluggish when cold. Reacts to ECM command to hold idle.. but slower, thus you see the effect as more pronounced.

Thanks, I will look up the big 3.
I just think its a little odd that it did not do this until I put in the 10w30, must just be a coincidence
Trippleblack, There is no noise coming from any of the pulleys under the hood.
Like I said, I will do a search on the big 3 and see what comes up and explore that option, I have only seen the truck do it once, my girlfriend has seen it do it 3-4 times at the most when cold, so I just assumed it had to do with turning the heat on and a little extra current/draw from the system.
Thanks for all the help. If it gets worse/consistent, I will be checking back.