i have an overheating issue

[relaxed]

ok heres the deal, this is my second 1st gen, my first was a 2.8, and i wont go there, so on to the question at hand. i picked up a 90 gmc s15 std cab short bed 2.5 5 speed. on the way home i noticed the exhaust leak, which turned out to be a hole in the muffler. but as i pulled out i noticed a lack of power. i know these arent the most powerful engine but its definitely lacking. 8 miles to the freeway everything good except the lack of power. as im on the freeway the temperature rose to damn near 265. never hit it but close so i get off the freeway. as im sitting at the light the temperature went down to normal no joke. start driving again and it rose. depending on my speed slower/lower or faster/hotter but it never overheated. what do you think might be causing this. its been sitting for a little over 8 months so my take is the tuneup and leaky muffler. and im gonna drain the tank and put in premium. all the hoses have been replaced, the water pump was installed a few months before parked. there are absolutely no leaks, oil, coolant, fuel nothing. other than the basics what do you think? also it has 70k miles original, owned by the original old man and never neglected. so i believe there is alot of life left in her. any suggestions? this is gonna be my last build of a mini so i want her to last, she will be in my family for as long as im alive so i want her done proper. im gonna start a thread on the total build after i get her runnin like "new" which is first on the priority list. also you think i got a deal, 90 std cab short bed 2.5 5 speed 70k original miles two very small dents everything intact with a/c already converted to r134a and all the maintainence records to boot for a mere grand. thanks ahead of time for all the help and input.

[lesterl]

Dont think you got hurt too bad, hows the coolant look? Does the upper hose get stiff and hot? Might be a water pump or a thermostat, I would change the TStat just for the heck of it, Eddie uses a 180* Stat and likes it better. I only gave $200 for my 89 with 60k, but I have to rebuild a motor (dont ask :-) Good luck man, maybe someone else has an idea?

[relaxed]

the coolant looks good, it was flushed when it was put up for sale last week. thats when he put in a new stat and hoses. to me the engine feels like its "loaded" up. meaning the power is there, but just cant seem to use it. im gonna try the tune up beings this is arizona and the weather here beats up on trucks and cars. i drove it around the block to get it to have the problem is there and it is. and what ive noticed now is it is difficult to get started again once its been extremely hot. thanks for the input its much appreciated.

[relaxed]

heres a couple pics of the newly acquired project.

[Steady Eddie]

relaxed---

265* is way too hot. Take the t-stat slam out of it, and try it again. If it runs somewhere "near" normal (or, way too cool, on the temp) then you've found your trouble. Your lack of power could be directly caused by the high heat. And, if it is very lean it'll run hot, too. From previous posts, here on the Forum, if it were me, I would put in a new AC Delco/Delphi
O2 sensor. Some Forum Members have reported a lean-out condition with NO trouble codes or SES light.
So you don't "know" that the thing is way lean. The replacing of the O2 sensor is a CYA thing with the Iron Duke.

I still believe that the Duke controls spark knock and pinging by monitoring the temperature, and the ignition module (with the the "help" of the ECU) has the ability to pull engine timing out of the advance tables, because the engine is too hot. I wanted to make sure that I never got close to a 212* F. coolant temperature, so I went with the 180* t-stat mod...which is, I think, a real good idea for Arizona, or most anywhere, if you want to run at full timing advance.

Also, a new t-stat CAN stick shut. If you decide to change it out, be sure to check it in a pan of water on the kitchen range, using a thermometer. You want it to open and close smoothly, with about a ten degree span, between open and shut...my 180* t-stat began to open at 176* and was fully open by 186*...a 10* span...

[relaxed]

thanks for the help brother, its much obliged. i started the tune up earlier today and so far have new plugs in it, and presto, already noticed a change in the running condition. a lil later im putting on the new wires cap and rotor. ill swing by autozone and grab a new stat and gasket. the thing that bothered me the most about it was it still got decent gas mileage. i drove damn near 40 miles and it hardly used anything, maybe and i mean maybe an 1/8 of a tank. so i think the tune up is a good start. the stat is next on the list. i need to get it roadworthy so i can take it in for emissions to get my tags and start driving her daily. keep the input coming in though i can use all the help i can get. i was a painter not a mechanic so i can unbolt and bolt, but nothing to extensive. thanks again.

[Steady Eddie]

relaxed--

You did not mention this:

If I were going to go through the terrible struggle that "could be" a distributor cap change, I'd damn sure put a new rotor in there......and, if you once got excellent mileage, what, besides the excess heat, changed?? I am thinking you may have a flaky O2 sensor...

[relaxed]

well you see i just acquired this truck and these are the problems on the trip home. it sat for i was told 6 months but more like 8. so who really knows when she was parked. the only issues really are, it can be a pain to start cold or hot. worse when hot. the temp being to high which is my major concern, and the lack of power. ive already noticed a difference with just the plugs like i said before. so the cap, rotor, and wires are a lil later tonight. along with a new 180 stat. i already put in some gas treatment and will top off my tank with premium after i get the new wires and etc on. i just need her road worthy to pass emissions, after that im gonna start replacing everything, egr, pcv, and so on. along with ignition coil, control module and so on. i want her to run perfect, which she is pretty close to already. and again thanks for the input i do appreciate it. im lost on these 4 bangers. my last dime had the boat anchor in it so im use to its "issues". i had to get away from it so i acquired a new project. thanks again.

[Steady Eddie]

relaxed---

One thing for sure, if you want your new-to-you 2.5L Iron Duke to pass a smog check, a new O2 sensor will REALLY help out with that.

And, like you said, once it passes smog, you can go on from there. Know this: You have come to the right place.

It is all about smooth running. EVERYTHING goes from there...your rig, compared to my rig, is brand new, as mine has over 192K miles....

[lesterl]

I wouldnt spend extra on premium, if nothing else drain the fuel and refill with good 87 octane.

[Steady Eddie]

Quote: Originally Posted by lesterl

I wouldnt spend extra on premium, if nothing else drain the fuel and refill with good 87 octane.

Yes, other than octane rating, as I understand it, for example, 87 octane Chevron Regular Unleaded, has the same amount of Techron as the Premium Chevron 92 octane...

[relaxed]

well i just finished up with the "tune up". so she now has new plugs, wires cap and rotor. she seems to be running alot better now. still need to change out the fuel which i think is the culprit of the hesistation and slight under power that im feeling. now update for the overheating issue. my brother walks out in the garage and looks down and says, "if your upper radiator hose is running over your a/c lines here, whats keeping it from getting pinch between them and the hood?" my response, "holy shit". i put a few lines of nail polish on the upper hose, closed the hood, and opened it, and sure as hell the nail polish transferred to the underside of the hood. so what im looking for is a couple good pics of the upper radiator hose routing. id like to see how you all have it ran. ill fix it when i put in my 180 stat. but i need some pics to see if its right or wrong in the first place. id take a pic of mine but the ol lady has it in her car. thanks for everything guys. im glad i came back to the forum. you all have always been a big help in the problems i encounter. ive been on here for a few years but took a hiatus when i got my new car. now she is gone and im back. thanks again guys its very appreciated.

[kamesama980]

for the overheating, I suggest backflushing the system or getting a new radiator. usually overheating on the highway then cooling off when stopped/slower is lack of radiator flow (either air over it or coolant in it)

[relaxed]

ok the overheating issue is solved, the previous mechanic or whatever you wanna call him had the hose on backwards. i flipped it around and presto no more getting pinched, no more overheating. so this is also a dead thread so if a mod can delete it thanks. and thanks for all the help. its appreciated.