Temp gauge fluctuates frequently at higher rpms

The truck is not overheating right now, it just seems like it's hotter than normal and like it's keeping the thermostat constantly opening and closing ( like no time in-between) ie- banging the thermostat!! Kinda makes me think the motor is getting hotter more often than before. Might just be that I'm nervous over nothing. But also the erratic idle mixed in the equation. And that might not have nothing to do with it. I could be a vac.leak I haven't found. As far as my oil. I replaced it every 3000 miles with redline syn. and it may be a waste but it don't have time to get dirty. So when I checked the stick and it was like it was when I put it in a couple weeks ago, I said it was good. I'll have more time tonight.

 

Ok. I made the trip back home and didn't have any problems. But I also kept the heat all the way hot with the fan low, just so it would hopefully help it not to overheat. And I did take it a little easier than normal. I ran it at about 2400rpms and normally I run it at 2800 rpms. And I also had a stiff headwind, most of the way home. Like a thirty miles an hour gust and 15 substained. So I had to keep it almost all the way down just to go 65. So needless to say it got pushed pretty good. So maybe it was the thermostat? But as I was driving into the wind I remembered it was kinda like that when it overheated. And so I was thinking that could my fan skirt that has been broken,( I taped it up a week ago) that is sitting back off the radiator at the top. Cause it not to get the air that it needed and maybe cause it to overheat? Like if I'm going 70 and the air coming through the grill end up pushing the skirt back even further. (See pic) . It never had hit the fan as far as I can tell. But I know it funnels air into the fan. And it was windy yesterday. Plus going 70. Could it have pushed it further back and disrupted the airflow? Would that cause it to overheat all the sudden? I've been running it like this for about three weeks but yesterday was the first day with alot of wind.I have all weekend to try to find out what happened. But I used a therm. from the parts store cause Toyota was closed , so I'm going to get a Toyota therm. and replace it and really clean my radiator. I'll either use a radiator flush or use some dishwasher detergent (Cascade). Hopefully if something else is wrong I'll find it this weekend before I have to go back to work. And guess I'll have to order a new IAC valve. Cause I was careful last time I put it all together and know I didn't miss anything. So I'm guessing I messed it up when I cleaned it out with carb cleaner. It was working fine before I took the throttle body off and cleaned everything. My worry with the high idle and the overheating that one time, is I'm just scared of a blown head gasket. Could a bad head gasket cause a high idle? If it can and a new IAC valve don't cure it, then I'll have an air test done.

 

Well, dag gumitt. It almost overheated again. It's been about a thousand miles since the last time. This time I caught it before it got to the red line. It was on the same 200 mile trip, on the way back and almost exactly in the same spot. My needle was about 3/4 of the way up when I noticed it so I slowed down to sixty mph and it didn't go any higher for a couple miles until I found a place to pull over. So I waited about five minutes and uesd rags and popped the rad.cap and let it shoot it all out. And apparently I didn't get it as clean as I thought I did from last time. Cause there was a bunch of rusty crud all over. I had plenty of water so I went ahead and took out the thermostat and filled it up and drove it home. Never overheated again. And hasn't since then. I did however flush it about ten times with radiator flush a few times and Cascade a few times. I've talked with several people and they all have different opinions. I do know that when I was flushing and driving it runs alot cooler with the thermostat out. Which makes me want to leave it out. But I've got to find the reason it overheated those two times a month apart. I'm hoping that it was just real dirty. I bypassed my heater core and replaced my fan clutch even though it had good resistance when it's cool. But a mechanic said he could see it slipping, so I had to start somewhere. I bought a Lisle combustion gas tester and the first time I used it , I believe I got water up in it and it turned yellow real fast, and the level in the tester came way up, so unless gases makes it exspand, I got water in the tester. So a buddy that works on farm equipment came out and said I probably got a false reading, so he tried it. This tester didn't come with a hand pump, it came with a hose to hook to a vac line. So when I hooked it up, it was bubbling like crazy and he said that was too much and unhooked it. So he just sucked on the line a little just to make a few stream of bubbles. He did it for about three minutes and it stayed blue. But my question is that should it be hooked up to a vac line to where it can really get alot of air going through there to where it's slawshing all around? Or just a steady stream of bubbles be enough? Cause I tested it a day later by sucking on the line and making sure I got more bubbles through it, and it stayed blue. It's been making me a nervous wreck thinking I might have a blown head gasket, as to why I brought that tester. But if it seems to y'all that I did it right then I'll feel alot better knowing that it's probably not that. And I just had alot of crap in my system.

 

Oh one more thing. I've been fighting an erratic idle every since I did a valve cover gasket job about two months ago. I had replaced the TPS sensor about six months ago, with a advance Auto (dormant) one. So I didn't think it was bad. And so I read some tread on here that said if you don't use a Toyota one that it would only last a few months. But I did everything to deal with the idle problem. So I found a Toyota TPS on line for a good price so I ordered it. I put it in a week ago and presto: idle is back to normal. About 700 rpm. I guess I got carb cleaner on the other one when I had the throttle body in my hand and I had it turned so I wouldn't get any cleaner on the IAC sensor. Even though I ended up taking it off and cleaning it. Doorman makes good parts and from what I learned from someone that worked for them , they do alot of testing to make sure their stuff is of good quality. But as far as the electrical sensors, I believe I'll stay with Toyota from now on. As with most of the other parts.