OK, here goes…. I have had an overheating problem with my 1986 Honda Civic 1.5L

12V carb. This has been an ongoing problem for, I’d say close to a year and a half.

So the problem is I am not getting any coolant flow through my radiator. The bottom

rad hose and radiator stay ice cold even though my engine temp is reaching max. My

temp gauge and temp sensor are reading fine, I have used a heat gun to check this.

The only way I am able to drive my car is by cranking the heat and staying off the

highway. I have a bleeder valve for the coolant, I bubble the system the coolant

starts to flow fine, fan kicks on, everything is good…Until I take it for a drive, it gets

air locked again, and I no longer have coolant flow and my engine starts to overheat.

So yes this does sound like a blown head gasket, but I start from the ground up

trying to solve this problem. First thing I did was replace the thermostat thinking it

might be stuck closed. That didn’t work, I put in a new radiator and rad cap, still

nothing. I check the water pump, it’s fine. I have no leaks, all hoses are good. So I

rip the head off, check the head gasket, looks fine, no sign of breakage. I get the

head cleaned up and the base milled, the head had minimal warpage. I buy a good

quality head gasket set, replaced all the seals, cleaned up the block really well put it

all back together all nice and pretty…you guessed it same deal.

I’m pretty frustrated by now, I figure it must be a cracked head, I go to the

wreckers, pull off a head clean it up, put it on, problem still remains. I consult a

mechanic, he tells me that it has to be a cracked head and that I must of just had

some bad luck and grabbed another cracked head. I wait until another one of my

cars shows up at the wreckers, and rip off yet another head. Clean it up put it on,

nothing has changed! Same symptoms exactly! I think I’m safe to say it isn’t the

head, so now I have 3 perfectly good heads and an engine that keeps overheating!

I know all of you are saying, just get rid of it, but I can’t let this car beat me. So the

only other thing I can think of now is, it must be a cracked block. So if any of you

have had experience with this car, and could lend any ideas as to what the problem

could possibly be besides a cracked block or any of the other things I have

mentioned above, I would greatly, greatly appreciate it. If I can’t find a solution I’m

grabbing the block that I took the last head off of and doing an engine swap. You can

understand my frustration, I am a 4th year mechanical engineering student, with the

little spare time that I do get I have done all this work outside in the winter, I just

want this problem to be solved! Anyways thanks for reading, hope someone can

help…

 

I can guess a couple things off the top of my head.
1) Possibly you have a bad radiator fan switch
2) Possibly your temp. gauge is faulty
3) Something is clogging your radiator causing it not to flow correctly
4) You have a airleak somewhere in your cooling system

Hopefully this helps and good luck

 

Thanks for the response! Although, I forgot to mention I did replace the fan switch too

with the radiator. I had confirmed that my temp gauge was accurate with a heat gun.

The coolant flows fine through the rad once I bubble all the air out, until I take it for a

test drive and it gets air locked again. Once it gets air locked it stays that way until i

bubble the air out of the system again, and the vicious circle continues. I agree with the

air leak in the cooling system, somehow air is getting into the system...

 

Are you loosing colant?

 

Nope...

 

Still using the same water pump? Tried replacing it?

Are all your coolant hoses on the back side of the head OK? The ones that feed the heater and warm the carb?

Did you bleed the air out of the coolant system?

Is your timing correct?

Scott

 

have you replaced your waterpump? I see you checked it for leaks, but like most pumps, if it sucking air in, it may not show a leak out. regardless, I would focus my attention from the inlet of the water pump back.

 

Actually, the water pump I have in there now came from a civic with 67 000kms on it. The only reason it was in the wreckers was because it had a blown hondamatic tranny. It made no difference, felt just like my other one too, both are in good shape. I have checked all the coolant lines very thoroughly they are in good shape. Yep, I bled air out several times but as soon as I start driving more air gets in and stops coolant flow. Just did the timing when I put this last head on. I went to the junkyard today and grabbed a block, gonna wait until school is done and do the swap, I have done absolutely everything and nothing has fixed it...Won't I look like a fool if it doesn't, oh well i have to try. Thanks for the reply scott.

 

A bad water pump makes a sound like a coffee can full of rocks....

You may have a blockage in your block... have you done a flush?

Bad timing will make your car run hot...

Scott

 

Have you tried letting it sit and idle for a while... Does air get in then?
I'm not sure I understood what you meant by one of your comments. Someone asked you if you were losing coolant and you said no. How are you not losing coolant and yet gaining air?
Other question... Do you have an aftermarket overflow reservoir? Is the hose from your radiator cap going to the bottom of the overflow reservoir? Because the hose from the cap has to be able to pull the coolant back into the radiator as the pressure changes. So, even if you have the OEM overflow reservoir, and the coolant tube isn't able to pull fluid back in, it would start pulling air.
Do you have access to a auto grade smoke machine? We have one in the lab at school. If you do, totally drain your system, find an adapter and fill that coolant system full of smoke. Where it comes out is where your problem is... You're probably going to have to stopper your overflow reservoir air bleed as well.
Best of luck!!

 

Yes bad timing will make your car run hot, but shouldn't stop the coolant from

flowing. Plus my timing is bang on, and my car runs and idles like a dream,

besides the whole overheating thing. No I am not losing any coolant, if I am it is

not noticeable. I haven't done a flush but when I first bleed all the air out, the

coolant circulates fine, so there are no blockages. My guess is I have a cracked

block, since it is not the head, and I am getting just enough air forced through that

crack on the down stroke to form an air bubble big enough to airlock my system.

Even a pinhole in the block could do this. Also when I am driving and the car starts

to reach 85-90% on the temp gauge, if I take it up to about 4500-5000 rpm, the

water pump forces the airpocketthrough, and my temp gauge will drop right down

to about 20% as the cold coolant from the rad flows through. After a little while the

heat will climb back up as the air builds up again at the thermostat housing. I still

have the stock overflow reservoir. I took it out cleaned it made sure the hose was

good, that was one of my first thoughts too, but everything was good. I'll check

about the smoke machine.

Anyways thanks for the tips guys!

 

I talked to one of my professors today and he seemed to second the cracked block idea, however he also said that a single test was worth a billion opinions...
The idea he came up with is to take an emissions tester wand and wave it over the open radiator... if you're getting hydrocarbons (fuel), it's a cracked block...
Apparently there's a tester with a name something to the effect of "Block Tester" that used a blue fluid that air is pulled through, apparently changing colors depending on the hydrocarbon level. It's also used above the open radiator.

 

Thanks a lot for going out of your way to ask your proff. about my problem, I appreciate that. I had looked at doing a combustion leak test, but the kit from Napa is like $50. I am fairly confident that it is a cracked block, so I'm just gonna go ahead and swap the engine at the end of April, after exams. If the new block solves the problem and it is good, I'll throw on new crankcase gasket set, and rings, maybe rod and main bearings, and I'll have a good running car for the next few years.

 

i'm pretty sure u got a wornout waterpump before u change the block i would change the waterpump to see if that help then go from there.

 

...I have changed the water pump, it's like new.

 

So it's 2023 and I have an 86 crx si with the exact same problem..been fighting it for 2yrs..did you ever figure out the problem? I've replaced my water pump and just tore down for head gasket..head gasket still like new..got 40000 on it and still mint.. irritating as hell

 

There was a talk some time ago on redpepperracing dot com about the different water pumps avail for our engines, and of course various non-OEM brands have different impellers , here is what I saved, the 515 has a slightly larger impeller