Jon Petersen

95 Civic EX coupe. D16Z6 engine. A few weeks back, I went on a short road trip, and I drove a total of 8 hours, give or take. She took it like a champ, but as soon as I got off the freeway at home, I noticed the temperature reading would go slightly above where it usually sat (still well below red) when I accelerated from a stop, then it would go back to normal. I got home and popped the hood, and the radiator cap was leaking pressure or at least that's what I assumed from the hissing sound coming out of it. Also, the coolant reservoir was way full.
More recently, I noticed the coolant was very low. I filled it, and within two days it's back to low again. No visible leaks, though I didn't get under the car so it's not impossible. When I squeeze the upper and lower hoses, they both seem fine, but the thermostat clicks when I squeeze the hose near it.
I'm thinking I need a new thermostat at least. Any ideas? Thanks for the help, I appreciate it.

TomCat39

I would replace the cap, also you have to bleed the cooling system when you add coolant, you can't just add coolant and run with it.

Once you've purged the system of air and replaced the cap, if you still lose coolant you need to begin checking for sources. One of them being a bad head gasket, another being a leaking heater core.

Usually when the recovery is full and you have major air pockets in the system (causes the temp gauge to bounce around) it's usually a bad head gasket.

Jon Petersen

Thanks man. I really appreciate it. Couple questions: what brand of cap? And to bleed it, you just loosen the bleed screw on the upper hose, right? And if it turns out to be a bad head gasket and I have to replace it, I want to turbo her in the future, so what head gasket should I use that could handle the boost? If you don't know, that's totally fine, I appreciate all the help you've offered.

Jon Petersen

Oh, and is it normal for the thermostat to click when I press the hose next to it?

Jon Petersen

Okay, so I replaced the thermostat, radiator cap, and flushed the coolant and bled it. I went on another 4 hour drive, and the temperature bounced around like it did before, but only after I got off the highway and let her idle for a few minutes. It went away after I turned her off for 5 minutes or so. When I returned home (another 4 hour drive) the temperature was fine, even when I got off the highway. The next day though, I checked the oil. The dipstick didn't have any oil on it. I started the engine for just a second, and some splashed up onto it, so I figure I must have burned a quart and a half (how much I had to add to get the oil level right) during the trip, since a week ago, the level was fine. Does this signal a bad head gasket, the oil and the coolant at the same time?

crazyhorse2011

its probably a typical high mileage honda d series motor. mine ate a quart of oil a month just from old rings and seals. A good indicator of blown headgasket is air bubbles rising up in the radiator with the engine runninig (take off radiator cap on cold engine and start). Coolant turbulence is normal, but bubbling signals exhaust gasses getting in cooling system. Or, oil sitting on top of the coolant. Or, milky white water inside the oil when you get a oil change. If you have none of that, i'd just forget about it and move on

crazyhorse2011

https://honda-tech.com/forums/honda-...3302851/page2/

TomCat39

The cap was a cheap item to rule out.

By bleeding it, what did you do?

The Honda process is to raise the nose of the car some (park on a mild incline or jack the front end up a touch.

Turn the heat slider to max hot (heater fan not required).

Open the rad cap (FSM says to loosen but not remove) and if you can, use a coolant spill proof bleeding funnel. Start the car and bring the coolant to the top of the filler neck.

Let the car run until the fan kicks on at least twice. ( got for 3 fan cycles ). At this stage, the car is supposed to be purged of air so you can put the radiator cap on and fill the reservoir to the max line. The radiator should be at the filler neck level at this point when you are putting the cap on fully.

Next morning, pop the rad cap off and if it's low top up the radiator and make sure the reservoir is at or only slightly above the minimum line.

If you forgot to put your heat to max hot, the heater core can trap an air pocket.

If you purge all the air, have a working cap, have no leaks anywhere and you get another air pocket in the system, it's a good sign the head gasket is starting to go.

Jon Petersen

okay, so I followed that process exactly, except that the cooling fan never kicked on, despite it running for nigh on ten minutes, I'm assuming because the ambient temperature wasn't high enough. The fan kicked on when the car started to overheat, so I think it's working, or at least the motor is.

Jon Petersen

I should clarify. The fan didn't turn on when I replaced the thermostat. The fan DID turn on when I pulled over during my roadtrip a couple days later.

TomCat39

It can take 20+ minutes for the car to reach operating temperature at idle before the fan starts kicking on. These motors are very efficient at cooling.

Jon Petersen

Okay, that's good to know. I'll bleed it again.

Jon Petersen

Question: I've heard Honda coolant is better than regular. Do you recommend using it? Or should I just stick with prestone?

Jon Petersen

Also, if I'm to bleed it, should I completely drain it and start over? Or should I empty the overflow tank and start as if I've just filled the radiator?

TomCat39

I've never used Prestone, I use Canadian Tire's motomaster Asian blend.

I think there is something about silicate free or something. My mechanic friend tends to use the bright lime green stuff. I prefer to stick to "Asian" blends so OEM, Honda or the Motomaster Asian model specific blend.

You don't need to drain anything to bleed. If the overflow is full, you should drain it to the min mark to start but that is it.

However, just know, I am not high in confidence that you don't have a head gasket problem. I suspect even after a true rebleed you may just end up with an air pocket again due to bad head gasket.

Consuming liter of oil in 500 KM is massive consumption.

Jon Petersen

Yeah, it's a lot of oil gone. I bled it for real this time, and some air bubbles came out, which is good.
2 things: First, last oil change, I sent in a sample to this lab that does oil analysis. They sent back that there was no detectable amount of antifreeze in the oil. Second, since I got the car, the coolant has been nice and bright green, but has had these dark grey wispy flakes in it. It could be oil, but I don't think so because of reason 1 and the fact that it's not the same color as engine oil. I'm thinking it's residue from the old overflow tank hose.

Jon Petersen

OH! Another thing to note is that the radiator is for a 4th gen Civic (88-91 I think). I know that generation radiator needed vacuum to pull coolant out of the overflow tank because of the cap having multiple stops, or something like that. I dunno if that helps, just thought I'd mention it.

Jon Petersen

Do you think I comec be burning that much oil because of a bad PCV valve?

tony_2018

With a car at cold start and doing the bleeding process it will take more than 45 minutes in order for the temps to rise. At idle. Not sure why folks keep thinking it's a quick process

EL Vap133

Just rev up the engine for a bit to help it reach the desired temp.

Jon Petersen

It took me 20 or so minutes to get the fan to come on 4 or 5 times. Is that long enough?

TomCat39

FSM states cycle rad fan twice to be considered bled.

It's my understanding the radiator creates a vacuum when the coolant cools and pulls the coolant back in from the reservoir. As well it's typicall 16 PSI valve to push coolant out when it heats.

I would be curious if the 4th gen radiator has enough cooling capacity for the car.

Jon Petersen

It's worked great for the year I've had the car. I'm on a vacation right now, and the 12 hours of freeway driving didn't phase it, except once when the temperature rose slightly when I got off to refill. My pops thinks it's just that the highway air isn't passing through it as much, so the temperature rises a little.

Kevs02Accord

Do they rent leak down testers at auto parts stores? That's what I ended up using to diagnose my bad gasket, didn't really take much time and told me exactly where the problem was.

Jon Petersen

They probably do, what's a leak down tester and how does it work? Also, do they rent compression testers?