AnotherOldJeepGuy

I'll go with a Fel-Pro! Got it! Rock Auto sells a Steel T-housing by Motorad (CH4802) and an Aluminum from FourSeasons (84802). Any benefit to one over the other? Is the original steel or aluminum? I didn't really take notice with I had it off last time. EDIT: Duh, all you need is a magnet to answer that last one, it appears what is there now is aluminum because my magnet doesn't stick! So I'll order the aluminum replacement.

So since I am going to put in a new tstat housing anyway, and as I look at Rock Auto for parts, I am wondering what the experts say about a few things. Thermostat: 1. 180 or 195 Degree Thermostat? The Rock Auto comments suggest 180 might be better for older/classic vehicles. 2. "High Flow" Thermostat? The Rock Auto comments suggests "a reduction in engine warm up times, allows trapped air in the cooling system to escape, and stabilizes the pressure of the cooling system overall". 3. "Fail-Safe" Thermostat? These have a lock-open feature in an overheat situation. I see less useful here, if I get an overheat I'm not planning to keep driving so other than an emergency that would demand it, I don't know that I am interested in this. I also note that I don't see both "Fail-Safe" and "High Flow", so if High Flow is a good thing, that's another reason I would not use the Fail-Safe one. Gasket: 4. On gasket, when I replaced my valve cover gasket it was Fel-Pro. The instructions specifically noted to not use sealant so I didn't and it is sealing fine. I tried to find the instructions that would come with the Fel-Pro thermostat housing gasket to see if they said the same thing but did not find that. I did ask my ai buddy and it said to install it dry unless there were lots of pits or imperfections. So, does the community agree with this, that is, if I get the Fel-Pro thermostat housing gasket, does it work without sealant?

I see one end at least in that posting. Not clear [to me at least] if that is the one Pentti was looking for, or the other end.

If you have the need to make it visible again, might go ahead and post that allusive pic for future reference.

I've watched while the temp came up from cold to around 190 and haven't been able to see it. But since the dye is showing, and that's the best clue I have, I'll work on what I can find and see what happens. When I have the thermostat housing off a few months back that housing wasn't in very good shape, and a new one isn't expensive so I guess I'll replace it and see what happens.

I used the REM to look at RPM with and without AC. There was about a 80 RPM increase or so with the AC on. So not a big change but in my case, some.

Data Collection #1 complete. I used 12oz. of fluid in 379 miles. I described my data collection and seep-only leak (no visible dripping or residue) to my favorite ai companion (duck.ai), and asked if the amount of coolant loss I measured could reasonable be expected for a seeping leak at the thermostat housing over the miles seen. The duck's math suggested it was. I don't really know if that's accurate or not, but, I still plan to try and eliminate the known leak, retest, and go from there....

I see why you are asking. I read your post and went out and looked, and to take the requested picture. No evidence of any ground at that described location I can find on my 4.0L 1990

Yeah I got the stepper motor (well 2 at the moment since I just put in a new one), but not the stepper motor exerciser . Just for fun I put in the number on the box from OHM's pic into an ebay search, the tester has turned into a fuel injuctor pump!!

Interesting stuff! No idea what that is either, but whatever it is, I don't have one! . It does answer the question of if the IAC is used in time other than IDLE, or at least I think it does and the answer seems to be yes as best I can tell. Doesn't say anything really of how it is used differently in different modes, but does say that it is used. It also mentions it does look at if the AC is on or not in IDLE Mode, although it doesn't really say anything about if the target IDLE RPM is intentionally being set differently with respect to the AC on/off or what that might be. So I decided I would ask my go-to ai (duck.ai) and the duck tells me a properly running 1990 4.0L Renix would see a 50-200 RPM increase if AC was turned on depending on various environmental conditions. That is probably a good enough answer to squelch my curiosity .

I went ahead and replaced the IAC just because the remaining thing here is idle is good with AC off but with AC on it's still a little less smooth. So the IAC is something fairly low cost and an easy minor hail mary, so I did it. The one I took out is from 1990 so I have got my money's worth out of it either way. It does seem a bit smoother, but that could be just me, or it could be real. Initial REM numbers are a bit lower, 118-122 where they were 129-130 on July 5. I don't know if that is "better" or not. Should the ECU maintain, or attempt to maintain the same idle RPM with AC on and AC off? The REM documentation says to expect RPM between 600-900 at idle, but also says it "should be around 750", but doesn't really say anything about if this is or is not with AC on. Does the IAC have any function other than at idle? I assume no, but I'll ask any since I don't really know and I'm sure the experts here do know!

As I understand it the ECU makes tweaks based on real time sensor input as well as historical inputs. I've been told here it can take as much as 40 startups for it to optimize. So if the IAC was a recent replacement to fix the problem, it could have actually fixed it but you might not be able to tell right away. This over time adjustment was what schooling the ECU was meaning. But since there is nothing you have just changed, that theory falls short. If you are really bored, you can read my recent conical that ended with this education being at the end and the step that finally got the issue from still failing to not failing, but bring some snacks, it's a long read

I recently had issues that I apparently fixed, but I had to give it about 25 miles running bad for the computer to realized it was fixed. If this started with the new IAC, or you just replaced the IAC attempting to fix it, there's a change you just need to school the ECU. The difference for me was night/day before and after the 25 miles of training. Also a common suggestion here is to make sure all your exhaust/intake bolts are tight, because they do tent to work loose. I know for a fact I improved things by finding a few a little loose and snugging them up.

Turns out I have quite a lot of specs that light up, and I expect a lot of them are not really something that can be cleaned away. But what I was able to determine was that the only glow that matched the expected glow was a small area at the thermostat housing. I was able to match this to the expected color by swabbing the inside of the dye bottle with a q-tip and comparing any glow I could find to the glow on the q-tip. This area at the housing is not an active leak, I can't see it leak. That housing was pretty ruff when I replaced the gasket a few months back when I put in a new water pump, and it did have to do it more than once to get (I though) installed with no leaks. This leak appears to be so small that I don't have a lot of confidence it is my only coolant loss, so the additional chemical analysis suggested will most likely still be done, but I'll try to eliminate this known leak first and see what happens. (note it's all wet because of some cleaning)

OK got my additive and flashlight, added the dye in today. I made one mistake I'll note here for the benefit of anyone referencing, I neglected to snoop around with the flashlight before putting in the dye. Why does that matter? It matters because the black-light flashlight doesn't only work on the dye! I can walk around my house and garage nowhere near my Jeep, and see things that will light up. So, while I do see some specs here and there in my engine compartment, I really don't know they were not already there. So for future reference, if you are doing this look around before you put the dye in and make note of any thing that already lights up! If you see anything, if you can, clean it off so that it doesn't shine, then later if you see a shine you will be sure it came from the dye! For me, this just means I need to clean up any specs I see, and drive around again. I learn something new every day on this "keep my Jeep running" journey!