windycivic

i have a 96 honda civic ex (vtec, manual) that has a very wierd overheating issue

i recently did a motor swap after my last engine seized up from overheating & have done everything to correct the problem of overheating with the new motor .
list of parts replaced include:

new head gasket kit(machined shopped)
new radiator
new water pump
jumped power to fan
bypassed the heating core
gutted the thermostat
new motor mounts when i did the swap

S.N my ac does not turn for whatever reason i can figure out, i do not have ac this was before i bypassed the heating core & gutted the thermostat

any advice helps.

Chance EG

Are you losing any coolant? When you say "gutted" the thermostat, you mean you have it 100% open now so coolant is always flowing? Check the coolant, see if there's any oil residue or smell/color to it (would indicate headgasket leak).

Could even be the radiator cap, did you replace the cap when you got the new rad?

rfmerrill

Did you bleed the air out of your coolant system?

windycivic

No coolant leaks, checked thru the whole cooling system pretty much every time I'm under the hood & can't find one. I have replaced the rad cap & yes there is coolant always running thru the motor 100 percent of the time(no thermostat at all). I had the head gasket job done to remedy the over heating problem originally & since have not found the oil mixing with coolant or coolant mixing in oil. The car says it over heats but I dont have coolant boiling over into the reservoir either so I have since changed the "ect sending unit" that sends info to the guage & checked that the guage is also working & it all checks out fine, also replaced the sensor on the thermostat housing.

Does anyone know if the car requires both fans to run at the same time regardless of the ac being used or not? since I only have the rad fan that works at the moment but I can always jump power to both fans if necessary

windycivic

my mechanic that helps me has done it each time we changed a part that correlates with the cooling system but I wouldn't mind advice on how to properly bleed the system myself

Ericjergs

AC fan is not needed to cool the car, and only turns on when the AC is on.

There are plenty of detailed writeups out there for bleeding the cooling system, but basically you just check the car up from the front, open the radiator cap, and let it run. Radiator opening needs to be highest part of the cooling system. You typically let it run for a couple cycles of the radiator fan, but since you don't have one I'd say 30 min to an hour depending on the how hot it is outside. Also squeeze the hoses to release trapped air when you're doing this. They say to run the heat, but you don't have that either haha.

Be sure to watch your temp gauge, don't want it overheating while sitting there.

fonkernuckle

iTrader: (5)

Sounds like you don't trust the gauge. any scanner will tell you the car's temp under live data. Give that a try and see how it compares to the gauge, normal temp is around 180

windycivic

We ran thru all of the above again (cooling flush. Bleed the system, etc) test drive the car & it was fine. Few days later i was driving on the highway 65-70mph for about 30min & than it started to overheat. At this point I think the car is possessed

windycivic

Could I just buy one of those bluetooth odb2 scanners & drive around with it to see what the temp is when the guage starts to show the car over heats?

BATmoREX

jonsey1886

In our civics there are THREE (3) sensors related to engine temp:

1.) The fan switch by the thermostat housing
2.) A ONE (1) wire sensor usually called "Thermo Unit" in the OEM parts diagrams-Yellow wire with Green stripe
3.) A TWO (2) wire sensor called "Sensor assembly-water temp"

Src: Majestic Honda parts diagram Under "Water Pump-Thermostat"

1.) Controls fan on/off with a variable resistor-when the hot coolant hits the sensor after t-stat opening electrical resistance drops, circuit is complete and fans cut on. Simple circuit NOTHING to do with PCM
2.) Simple Negative temp coefficient (NTC) sensor controls the CLUSTER temp display, again straight(ish) wire from sensor to cluster nothing to do with PCM
3.) Sends coolant temp info to the PCM

Src: MitchellOnDemand/ProDemand wire diagrams

So which one did you replace? Number 2 or number 3? Honda set this up as a bit of a fail safe, to provide an exacting accurate value to the PCM while also giving an inexact value to the gauge cluster to prevent needle jump and inadvertent driver overreaction. As far as bleeding a cooling system-check this out:

https://www.ericthecarguy.com/faq/wh...ystem-problems

StayKrafty

With car cool and off, remove radiator cap and start the the car without the cap. Did coolant shoot out?

fonkernuckle

iTrader: (5)

Yes I have one of the blue tooth scanner bluedriver and it does show actual temp under live data

windycivic

I will try to bleed the system again. I replaced thermostat & bypass the heater hoses because the mechanic said the heater core was clogged(we live in Florida anyway)

windycivic

if I'm correct we replace 2 & 3. We never replaced the fan switch because we jumped power to fan anyway

mk378

Why is the heater core clogged? Did someone put stop-leak in it? In that case you likely need a new radiator.

Overheating from a prolonged highway run is very often due to a slow leak in the head gasket. The test to run the engine cold with the radiator cap off is one of the ways to check. Head gasket denial runs deep in DIY car forums.

GiantDad

A leakdown test will tell you whether or not your headgasket is blown. If you see bubbles or hear activity, your gasket is blown.

tony_2018

So, is your replacement motor overheating too?

windycivic

I had an OEM rad installed brand new before we bypassed the heating core & it still over heated we also just did the head gasket because that was the original overheating issue & even went as far as putting another all new aluminum radiator to be on the safe side . I've vigorously checked all the fluids after each drive & my coolant & oil check out fine so I'd be highly upset if I just forked out all the money to have the same issue with the head gasket

windycivic

what is the leakdown test? Simply pour water over the motor?

are the fan for the radiator a multispeed clutch fan for different operating temps I also read somewhere that the thermoswitch for the fan will turn on both fans when a certain temp is reached(200 ir something I think) I only have one

GiantDad

lol no.

I'll just copy paste what I said earlier.
A leakdown test is easy on a gasoline engine, try it out.
Calibrate the leakdown tester, remove spark and insert correct fitting with hose and balloon attached.

Rotate engine BY HAND clockwise and wait for the balloon to fill and enlarge, then remove hose and insert a brass rod or plastic rod into the cylinder.
Keep cranking until it the rod reaches maximum hight, this means you are on TDC of the compression stroke.

If you miss TDC, DO NOT rotate engine backwards, you could jump the timing belt.
Anyways, once at TDC on the compression stroke, install leakdown and pump the cylinder full of air.

Noise from intake manifold/air filter housing = bad intake valve or valve components.
Noise from exhaust pipe = bad intake valve or valve components.
Noise from oil filler cap = piston rings

In you're case, you're worried about noise and activity in your radiator and coolant reservoir.

You don't want to hook it up, pump it with air and start cranking away, because you risk blowing the cylinder walls bonedry of oil, which is not good.
Do you own an air compressor?

mk378

Leakdown test is to remove the spark plug and inject air into a cylinder (from a regular air compressor at about 100 psi) with the engine not turning. If there is a leaky head gasket, or a crack in the head or the block, the air will appear in the radiator.

Most compression gauges can be used for a simple leakdown test by detaching the gauge head and removing the check valve from the spark plug end of the hose. The gauge end fitting fits on a standard shop air line.

windycivic

Sounds easy enough. I dont have a compressor but I have access to one

rfmerrill

Edit: wrong thread

Relic1

when does it overheat? moving, sitting still, both?

**edit**
summary of my thoughts: (yes you have eliminated some of these all ready, just making a check list)

general causes of overheating:
air trapped in coolant system
water pump
clogged radiator
radiator cap
lower radiator hose bad (constricting when flow occurs)
thermostat not opening
radiator undersized
engine issue (coolant passages restricting or blockage inside engine)
head gasket issue
bad temperature sensor (either the gauge sensor, ECU sensor or fan switch)

Standing still overheating problem:
fan not working or undersized

Moving overheating issues
fan working all the time (restricts air flow)