Climbing cruise temperature

[EliRush]

Hi all,
I am new here, and I did several searches without finding an answer...for a pretty silly question...

Where is the fuel mixture screw on a 1986 3AC stock carb? Once I find it, is it clockwise for rich, counter-clockwise for lean?

I am running hot at cruise, and everything is tight with the cooling system. I think the mixture was adjusted without me present, and just want to see if it is running too lean. I know about pulling plugs and whatnot...I am just not up on the mix screws...and where it is on this carb!

Thanks!

[dlb]

carb adjustment in the factory service manual starts at FU-19, or page 169. the link to the FSM is found at the top of every page on the forum.

i believe the fuel mixture can only be adjusted for idle, not for cruising. that is determined by the size of the jets. i could be wrong though, as i'm a carb newb. anyway, the idle fuel mixture screw is hidden/protected by a cap. check out the FSM, FU-28 or page 178.

[EliRush]

Thanks! I will check that location on the carb and see if it has been drilled out before. I didn't see that link...right in front of me the whole time. Derp.

If it hasn't been drilled out (adjusted from spec), and the cooling system is working good...why would it run hot at cruise? New radiator, and the air has 'burped' out. It doesn't consume coolant, and runs like a top otherwise. It fluctuates up and down a little while driving surface streets (still in middle), but take it for a highway cruise and it climbs up until it is about 3/4 up on the gauge. I did some research here, and I think the other guy hadn't burped the air out of his.

Would any of the vacuum lines have anything to do with that? I capped the large line going from the side of the carb to the air cleaner, per instructions on another post. It really improved the smoothness and cold starts...but this weird running hot issue has come up....are they related?

[arbskynxnex]

There are a few things you could look at. You might check the thermostat and water pump, or maybe the catalytic converter or muffler are plugged and its backing up the exhaust. I think off timing could cause those symptoms too. You should also check to make sure the Hot air intake shuts once the car is warmed up, that would be the large pipe from the exhaust manifold to the air cleaner.

[Petros]

There a few things that can cause that kind of reaction. If the radiator is internally coated of paralytically plugged it will run hot when put under loads, it will be noticeable when climbing a long hill: temp climbs as it the load goes up, down as you reach the top of the hill and load goes down. Solution is to flush the rad out with chemicals, or replace it. A radiator shop can test the cooling capacity of the radiator with a heat gun to verify it is a bad radiator or not.

A collapsed lower radiator hose can cut off coolant supply, it should be stiff enough to prevent it collapsed when the engine is reved up (pumps suction can collapse it). Replace the hoses if it gets sucked flat.

A marginal thermostat can also act that way, best to replace them about every two years. Do not buy the cheap ones ($7-8), some of those are junk right out of the box. Get the premium thermostat, but $15-18, or a Toytota factory t-stat.

Bad timing setting, too far retarded, will also make it run hot. Set it at 10 deg BTDC, except when going to get pass emissions, than set it at the factory 5 deg.

One other thing can make it act like that, running too lean. That will not be caused by an adjustment since only idle mixture can be adjusted. It means either the carb needs to be cleaned out (or rebuilt), or you have a vac leak in one of the many vac lines or vac operated devices. inspect them all for a leak, if you cant find one try carb cleaner spary with the engine running, spary it all over everything and see if the engine speed changes when you do.

Good luck

[EliRush]

Thanks for the advice, I have been looking at it today. The solutions with the highest probability are the collapsed hose (it felt squishy), the thermostat, and the vacuum leaks. I have been looking for leaks since I got it, and capping them or fixing them. One thing I have noticed is that there is a small vac port on the front of the carb that keeps losing caps. I guess it is putting pressure on the cap, not sucking on it. The small cylinder on the very front top of the carb is the one popping off the caps.

I also took the air cleaner heater hose and snorkel off of the cleaner, since the vac hot air door wasn't operational anyway. What about an open element air cleaner? Can't seem to find one easily.

Something I should mention is that the wire to the top coolant temp sensor (on front/top of engine) had a broken wire, so I replaced it with a wire of the same gauge. I made good contacts, and I didn't see it as an issue before...but now...?

I'll let you know what happens with the hose and stat. Or I'll come back and ask more questions when I find something else I don't know.

EDIT: I am looking for a performance t-stat, and see a few brands. Can you recommend one that will open colder than stock? Less than 180 degrees (from what I read), and reliable?

[EliRush]

Wow...replaced the radiator cap because I noticed it was leaking. Problem is gone. wth?



I'll take it.

[Petros]

The cap is actually a pressure relief valve, it is supposed to maintain the system pressure for it to cool properly. If the gasket is shot, or the spring weak, it will allow the coolant to boil and not cool properly. So yes, a properly working cap is important, but it may not be your only issue, so keep an eye on it.

[EliRush]

Ok, the problem is fixed, if I don't go above 55 mph. I can drive it for about 30-40 minutes, then when I get onto the 4 laner I go about 60-65 and it starts moving up. It seems to be worse at night? Here's the kicker...as soon as I hit a flat stretch and zoom up to 75-80 the temp goes WAY DOWN to a little under halfway and will stay there until I back off. I don't want to stress it out by going that fast, but I did it twice for science.

So, it only overheats at 60-65. And it really doesn't overheat, it just reaches about 3/4 up and stays there. I have thought about airflow...but what if the revs of the engine are just pushing coolant quickly past a half-open thermostat? I got a tstat to put in it, just because...so we will see.

[EliRush]

Thermostat.