Odd overheating issue (and oil question)

'93 Civic Cdn CX with an original computer (P08) and a non-original
engine (D16Z6 - the D15 engine died a while ago) with a new radiator
(installed with the Z6 engine a little over a year ago) - this problem
showed up only in the past month.

Engine comes up to just-below-midpoint temperature reading normally.
After long drives (i.e. engine warmed up) when left idling (red
traffic light, stuck in traffic, etc) temperature reading starts
climbing. I've seen it go almost to the red line. If the engine RPMs
are brought up the temperature will come back to normal - either
through normal driving, or by putting the car in neutral (with brakes
on, of course) and gently touching the gas.

Any sort of engine load (RPMs up) and the temperature regulates
properly.

Coolant level looks OK - there's fluid in the overflow tank and the
inside rubber hose is 'wet'. Color is green, looks clear.

When the engine is warm, the 'low idle' seems to be quite low -
sometimes the engine seems to want to stall. I wonder if this very low
idle mode isn't conducive to proper coolant flow. Any other theories?
Water pump, maybe?

Second question: my mechanic is fairly insistent that older Honda
engines (> 200000 km) tend to start consuming oil, and that this isn't
a big concern. Agree/disagree, anyone?

I'm about 1500 km into an oil change and noticed that the dipstick
level has come down from 'full' to halfway between the dots. I also
see some oil under the engine on the driver's side where the plastic
of the bumper comes in under the engine compartment, so I suspect a
slow leak more than actual oil burning (tailpipe doesn't show any
signs of oil burning).

 

not the water pump. does the electric cooling fan come on? does the
thermostat operate properly? [best to replace because it's now old
anyway.] are the radiator fins clogged with leaves/mud/insect debris?

low idle is another issue. ensure the ignition system is healthy,
correctly adjusted and that the idle system works within spec.

some burn a little oil, yes. unless it's excessive, it's not a concern,
no. and some oils burn off more than others.

that's within spec.

it won't show signs on the tail pipe unless the catalyst is completely
shot. check the oil pan for bolt tightness, and try using a quality oil
with proper seal conditioners in it. also check the pcv valve.

 

i'll check the fan. the rad is definitely clean, as as for the
thermostat, it's probably original.

i replaced the pcv valve not long ago, the old one was most likely
original and was stuck open. i'll have a look at the oil pan.

thanks for the advice.

 

Hi,
Basic thing first. You know for sure fan comes on when it supposes to?

 

i verified that the fan is working - when the temperature gauge comes
up to around mid-point, the fan cuts in.

i decided to replace the thermostat - what i found in my engine is
best described by a picture.

http://www.flickr.com/photos/angstful_mfg_employee/2724998691/

needless to say, i *don't* think they're supposed to look like that!

(incidentally, the haynes manual underneath it says to pull off the
upper rad hose to get to the thermostat ... uh, no, that would be the
*lower* one - i'm very thankful that I have a PDF of the Honda shop
manual)

a quick test after purging shows improvement. i could feel flow
through the top radiator hose (it got warm) and the temperature gauge
was stable. i still have to take the car for a short tour before i
judge success or failure.

the rubber gasket and o-ring around the thermostat are showing signs
of deterioration. i can live with a slow leak until i can get to the
dealership and get those
replacement parts. it appears that the coolant needs replacement
anyway (looks a little cloudy).

 

that's not a honda oem thermostat. for a few dollars more, it's worth
getting the real deal - much better temperature control /and/ the
correct vent valve. it also comes with the rubber gasket.

you should replace that stuff periodically anyway. use distilled water
as the dilutant.

 

no overheats yesterday. yay!

i took the car in to get the coolant system flushed and refilled. the
mechanic told me that there's combustion gas coming out of the
radiator, he suspects a head gasket problem (or worse, maybe a crack).

i'm not convinced that this engine is going to last much longer.
considering the amount of $ involved to even find out what's going on,
i'm seriously consdering getting a new car and being done with it.

 

it's easy enough to check for yourself. and if this person couldn't
figure out the thermostat before, you absolutely cannot trust them on a
head gasket diagnosis.

simply look for bubbles in the expansion bottle. drive the car around
for about 20 minutes to get it to full working temperature, then
carefully unscrew the lid of the expansion bottle [NOT the radiator].
hold the lid to one side so that the tube inside is still below the
surface of the liquid, but so that you can see in. use a flashlight if
necessary, then observe for bubbles. if you see any, the head gasket is
indeed shot. if not, then it isn't!

replacement jdm engines are seriously cheap. if your body is unrusted,
it's more economic to replace the motor than to replace the car. and if
you do consider replacement, be sure you're going to be satisfied with
the handling of the new vehicle. one of the reasons i stick with the
old stuff is that every time i try a new one with macpherson front
suspension, i'm disappointed. gotta love the old honda wishbone civics.

 

it's easy enough to check for yourself.  and if this person couldn't

no diagnosis of the overheat problem had ever been made by this
particular mechanic. in fact, this wasn't my regular mechanic - my
regular guy isn't open on sundays, and since this should have been a
simple drain/flush/refill, i trusted it to a local mass-market shop
(cdn. tire)

the engine from which the incorrect thermostat was pulled was
installed in the car around a year ago by my regular mechanic. i
suspect that the engine had this particular thermostat in it when it
was delivered to him.

should this engine turn out to not be economically repairable, i'd
have a hard time coming to grips with a second replacement.

well worth checking. what concerns me is that if the head isn't shot,
how could combustion gases make their way to the radiator?

 

misdiagnosis.

bubbles are either improperly purged system, leaking head gasket, or
cracked cylinder/head. there are no other possibilities.

 

misdiagnosis.

i followed the 'haynes' procedure for purging the air out of the
system after replacing the thermostat:

- close all drains
- open air bleed valve on top radiator hose
- slowly fill rad until fluid runs clear through air bleed valve (no
bubbles)
- close air bleed valve, top up overfill reservoir
- keep rad cover open, operate engine until therostat opens up and top
hose gets hot
- shut down engine, top up radiator to fill lip
- top up rad to fill lip and close rad cover

the thermostat is keeping constant at slightly-below-half, so i don't
think there's an immediate cooling problem.