Proper Radiator Cap Pressure Rating for 1994 Honda Accord EX?

1994 Honda Accord EX, 4 door
4 cylinder, Automatic Transmission

I just recently replaced the Radiator fan motor, and now both my AC fan
and Radiator fan seem to be capable of turning on and off. However,
I don't think that they are turning on soon enough. With the recent hot
weather here in PA, if I idle the car with the AC off, I've noticed that
the temperature gauge needle will rise to just under the red zone (hot),
and then both fans (AC and Radiator) will come on, cool things a
little, turn off and then cycle on and off as they should, but at a
generally
higher temperature than I remember in the past. The radiator cap is rated at
13 psi. Is this the correct rating for the above vehicle? I am wondering if
it
may have been accidentally replaced last summer.

Thanks,

Gary

 

before worrying about the cap pressure, consider the following:

when was the thermostat last replaced?

in what condition is the radiator? is it clogged/sludged? filled with
bugs?

what level is the coolant? are you losing any? any bubbles in it?
[check inside the radiator, not just look at the expansion bottle.]

 

The thermostat was replaced last summer. When I looked into the
radiator recently I did not see anything particulary unsightly, but I
suspect that it may have been six years and 50K since the antifreeze
has been changed. I keep the coolant level between Cold and Hot, and
I don't appear to be losing any. I thought that I saw bubbles once in the
expansion bottle, so I fiddled with the radiator cap, and they seemed
to go away. I imagine that I could be due for some kind of radiator
flush and antifreeze replacement. The antifreeze doesn't look too bad,
but I suspect I've seen cleaner.

I called an auto parts place just to see what pressure rating was listed for
my Honda Accord's radiator cap and they said 16 psi. Since the one that
I have is 13 psi I wonder if it is the wrong radiator cap, and if it would
make a
significant difference in the ECT sensor's ability to turn the fans on at
the correct
temperature.

Or, is six year old antifreeze more likely to be a factor?


Thanks,
Gary

 

The temperature level should not go above the 1/4 mark on he 94-97
models. On my 95 Accord in the 9 years that I have owned it never went
past that mark. You could have some air in the system. I would suggest
that you purge that air out first and go from there. I'm not certain
if the cap could be a problem but just to rule out any possibilities,
I'd get one from your local Honda dealer. They shouldn't be that
expensive to get and it's one thing to rule out of the checklist.

Good Luck,
Nick

 

hard to change the thermostat without changing the coolant.

hmm, that's suspect.

can't hurt.

no, it won't affect that at all. a higher pressure cap just elevates
the boiling point a little.

not unless it's really dirty. check the thermal switch and the fan
relays for operation. if the switch checks out ok, to eliminate the
head gasket as a suspect, have a chemical test done on the coolant to
see if there's exhaust gas in there. then look at the radiator again.
they fill up with bugs and all kinds of other debris that impairs
airflow significantly. if replacement is in order, i've had good
experience with these folks:

http://catalog.eautopartscatalog.com/ipb/wizard.jsp?partner=ipb&clientid=alleurasianautoparts&baseurl=http://www.alleurasianautoparts.com/&cookieid=1TU0Y4A0K1US16U12G&year=1994&make=HO&model=ACC-EX2-002&category=G&part=Radiator&appTransmissionType=Automatic

i'd go plastic tank.

 

Only if you do the job with the car upside down.

 

ok, let's be pedantic because you know i'm like that. the elevation of
the thermostat relative to the engine block is about 2/3rds the height
of the whole. and of that, the head carries a significant quantity of
the coolant. for the engine, i therefore estimate you'll lose roughly
1/2 its fill of coolant. for the radiator, i estimate roughly 1/3rd.
hoses, maybe another 1/3rd. that makes roughly 40% of the coolant
changes with a thermostat. that's a higher percentage than you can
change on the automatic transmission.

 

This car is mostly driven on short trips over country roads. It is only
recently that we are
having really hot weather here in PA, so I suspect that this problem may
have existed
for awhile, possibly since last summer. Yesterday was particularly hot, and
I drove the
car for about an hour before I noticed that the fans were cycling at a
higher than
expected temperature (around the 3/4 mark). Overnight things cooled off, and
when
I checked the antifreeze reservoir, it looked like the radiator may have
sipped about
a pint out of it. I removed the radiator cap, started up the engine and
added antifreeze
whenever I could. I would say that it may have taken another pint . Now the
fans are back
to cycling on and off at about the 1/4 mark as Nick indicated. So I think
that might be back
in business. I did notice some things when I purged the radiator:

1) I would sometimes see bubbles coming from the coolant at the radiator
fill.
2) The level of coolant would go up and sometimes overflow
the radiator when I revved the engine up to about 2000 RPM.

Do either of these things imply a bad head gasket? If so, maybe that is the
reason that I needed to
add coolant. If not, maybe the radiator was never properly purged last
summer when the thermostat
was changed.

How can you tell when the thermostat opens? Does the big hose on top of the
radiator become
pressurized?

Thanks everyone for all the help.

Gary

 

excellent. you'll see gas mileage improve now too!

that's normal when refilling. fill it as much as you can, then put the
cap back on and crack open the bleed nipple. let some air out, close,
rev the engine, and crack open the nipple one more time. bubbles you
see after a few minutes and at full working temperature are suspect.
keep the heater full on while doing this too.

that's normal - don't worry about it. the fluid expands as it gets warm
and will surge as the pump increases pressure.

let's say the system was never purged. replenish accordingly, but stay
on top of this situation by checking daily. the early stages of a
gasket failure have very minor symptoms and may persist for a
considerable period before they get bad enough to warrant surgery.

there will be pressure, but that's not a result of the thermostat
function - pressure is equal throughout the system. the thermostat's
open when the /bottom/ hose gets hot.

 

I don't know what I'd call you, except it's not "pedantic."
Let's just be honest.

One does not have to change the coolant on all Hondas after
a thermostat change.

Have a gallon of coolant (OEM or whatever is used in the
car) on hand, because one certainly will lose some.

That's the ball park.

 

Where is the bleed nipple on the radiator. Is it possible that some
radiators don't have one. Or are some radiator caps equipped with a bleed
nipple?

Thanks,
Gary

 

it's not on the radiator - it's on the aluminum engine casting where one
of the big radiator hoses connect.

 

Check the thermostat rating. You should be using a DEALER thermostat, with
a rating of 78C. A 90C (190F) thermostat will cause overheating.

Also, your rad cap should be stamped "1.1" bar, or about 16lbs. A 13lb cap
is stamped "0.9".

 

The thermostat was replaced last summer. Hopefully, the mechanic used the
correct one.
Recent purging of the system seems to have helped, but I suspect that
something is still
wrong, and that I should change the radiator cap. The actual installed
radiator cap is
stamped "13lb" and "0.9", so it appears to be the wrong one. Does this mean
that the coolant
would be inclined to boil prematurely, and if so, what effect would that
have? Would boiling
coolant impair the ability of the temperature gauge sensor and ECT sensor to
sense the proper
temperature and respond properly? Would boiling coolant effect the tarnsfer
of heat from the
block to the coolant?

Is there any reason why one would intentionally install a radiator cap with
a 13lb rating instead
of 16lb? A car with 300K is certainly a candidate for a blown head gasket.
Would installing a
lower pressure rated 13lb radiator cap instead of a 16lb cap be a good way
to keep coolant from
being blown out the exhaust pipe?

Thanks,

Gary

 

It's possible. Change the cap with new OEM, top up the rad and see what
happens. The critical thing is that the reservoir level should rise with a
hot engine, but then go back down to its usual cold level when cold again.
If it does not, the water is being displaced with air. By the way, this can
also happen if the fluid connection between reservoir and rad filler neck
is compromised. If there is a leak in that circuit, the engine will be
unable to suck coolant back into the rad as it cools.

At this point, reading this thread through, I'm suspecting a failed head
gasket. Your low coolant level, bubbles in the reservoir, overheating at
idle...bad signs. You need to investigate that possibility if s new OEM rad
cap doesn't help.

Mistake. But their operating ranges overlap, so this should not be a
disaster. A blown head gasket will cause more problems than the wrong cap.

You bet. Get a"pressure test" (NOT a "compression test") done. Some garages
can do a chemical test for combustion gases in the coolant, which is
probably better.

In your case, probably not. I'd replace the cap and top up the coolant in
the rad. If that doesn't work, get the head gasket checked as above.

 

I installed a cap. It was not a dealer cap, but it looks just like one. My
radiator is probably an
aftermarket one. I know the radiator fan is NipponDenzo, and I think the
radiator is also. There
is no writing on the radiator to identify it. I've seen the Toyo radiator
cap, and I don't think it
would work on my radiator, so I think that the "NipponDenzo type" cap is the
correct cap.

At this time, the reservoir level increases when the engine heats up, but
still stays at that
elevated level when the engine cools down. The radiator and AC fans cycle on
and off properly,
and the temperature gauge stays steady about 1/4 of the way up from C
(Cold). If I open up the
radiator cap in the morning when it is cool, I usually have to add about 2
or 3 cups of
coolant. There are no more bubbles in the coolant, and there are no coolant
leaks
anywhere on the ground under the car or on the engine or radiator. No
unusual exhaust,
and the oil looks normal.

Either I am still purging the system of air or I am in the early stages of a
head gasket problem.
The thermostat was replaced last summer. If it was mistakenly replaced with
the 90C instead of the
78C, then my engine block could be 12C higher than it should be. Would this
put undo strain on
the head gasket? If it turns out to be a headgasket problem, would it be
wise to use the 13lb
radiator cap instead of the 16lb?

Thanks

 

Bad, bad, bad sign. Very bad.

Check this though: The line running from rad filler neck to the bottom of
the expansion reservoir tube. If it has been breached in *any* way, the
engine will not be able to suck in fluid as it cools, but will suck air
instead. The connection must be *absolutely* airtight.

I vote for the second one (if the expansion hose is OK). Better get it
looked at. Failure to quickly address a possible failed head gasket will
result in a greatly increased chance of making the engine uneconomic to
repair.

Make haste to a garage. Don't fool around with rad caps any more.

 

I checked this line throughly and, unfortunately, it has no problems. I
guess
I have some kind of gasket problem.

I did find out from my mechanic that he installed the 90C thermostat, and
not the
OEM 78C one. I wonder if that might have some effect on this condition. When
I shut the engine off and it cools down, the thermostat closes at 90C
instead of
78C. If I changed the thermostat to the OEM 78C one, would the engine
somehow
have an improved opportunity to draw coolant from the reservoir? Would the
thermostat being open for that additional 12C differential create more
suction from the
reservoir as opposed to through the head gasket? Does that make any sense or
is it just
"wishful thinking"?

Thanks again

 

Oh, that changes everything!

I did mention to check that, a few posts ago.

You have it sort of backwards. It *begins to open* at 90C, which is WELL
above the proper temperature for that motor.

A 90C thermostat will cause the car to overheat. Your mechanic has
committed a serious mistake here.

Replacing the thermostat is certainly worth a try.

If the fluid boils so as to cause the top of the rad to be filled with gas
and not fluid, the engine will be unable to pull fluid from the reservoir
back into the rad.

Put the proper **DEALER** thermostat in and see what happens.

 

what tegger said.

wrong thermostat is not good. consider a different mechanic in the future.