enygma64

hey people

did a search but really new to hondas and this site...

tried to be as thorough as possible in desciption

1986 civic hb Si started idling wierd lately. last spring changed out radiator, fan switch, wp -seems to be related to a temp sensor is why i say this.
used to run great at just under 1/2 on temp gauge all summer
...now
starts fine; idles high while cold 1800 +/-; warms up reasonably fast;
gets to about 1/ 2 on temp gauge and then slowly the idle speed increases;
when it gets to 1800 or so it drops then cycles (like a vacuum leak) from 1800 to 800 and back in a couple seconds;
car then heats up quickly while doing this cycling; (i usually turn in interior fan to cool it down)
if/ when it gets to the line just under hot/ red area, it smooths out at normal! also fan does not start?
as it cools down a bit it will start cycling again?!

while driving i can slow down with brake and not depress clutch till almost stopped and engine slows to 200-300 rpm, then put the clutch in while stopped and it will idle about correct (800+/-) for a minute or two.

read in manual it might be TAS, coolant temp sensor, or air intake temp sensor,

leaning toward temp sensors but cant find good/ easy tests to determine which

OR am i completely wrong?

any help appreciated

E-AT_me

re-bleed your coolant. you may have a bubble somewhere of air.. either that or replace your thermostat.. the fan should be kicking on. are you sure the fan switch is good?

enygma64

thank you sooo much that makes sense.

so upon trying to bleed it at first i get nothing!!! (when i bleed is rad cap on or off?)
then it pulses a bit but never flows evenly. so air is obviously present.
greater flow when i increase rpm but still inconsistent...
the coolant is still up to rad neck
thinkin the t-stat is not opening? where/how does the air get in? from boiling of coolant?

hopin its not water pump- it seemed pretty bulletproof when i redid the system last spring.

also the lower hose (from t-stat housing) seems pretty cool and soft like no coolant? even when upper is pretty hot?

flow is definitely restricted somewhere seems...

also fan runs at very hottest temps - is it 2 supposed to be 2 stage?

E-AT_me

get a new t-stat. bottom hose should be just as hot as top. water will boil and add air to the system.

if the water pump was bad, it has a weep hole that usually will weep coolant.

enygma64

ok cool thanks!

the old weep hole clue- that helps point the finger at the t-stat for sure!

the hose thing had me pretty sure but i replaced the t-stat last spring, oh well.

really appreciate your help!