Hi, I am having an overheating issue (big surprise huh?) that I've tried a bunch of stuff and trying to figure out what to try next. Lots of info in forums, guides, and manuals already, but I'm starting to get to the bigger stuff and wondering if there's any symptoms or checks to try before doing them.

It's an 86 non-turbo in excellent condition.

The problem:
Gets hotter than it should be getting and once went above the 240 line on a steep grade and spewed into the overflow, boiling. In hotter weather, it gets up close to the 240 line quickly without driving it very hard....like 5 miles on the freeway does it.

Things that make it overheat:
- Running high revs
- Hotter weather
- Going up long grades on trips


Things done to it and things to note...

- Coolant flush
- No leaks anywhere, burped it correctly
- Replaced all hoses
- Replaced the pressure cap
- Replaced the thermostat
- Fan clutch looks good (the right play, no visible signs of problems, no noise, no wobble).
- Overflow tank is at correct level and working ok
- Radiator is clear of debris

Other things to note:

When starting the car again after it's been sitting for 15 or so minutes, the idle fluctuates up and down from 700 to 1100 rpm for a minute or so until the engine heats up again. I've got a long list going about why this might be happening, and may or may not be related. It doesn't seem like it from forum discussions and the list of things I'm going to try to fix it. AND, it was overheating BEFORE this started happenning.

There have been some electrical issues lately (yeah big surprise huh?), but I don't think they're related in any way. The radio went out entirely, there is a clicking noise coming from the relays for the a/c occasionally (haven't traced the line while they click yet because it's so infrequent).

The engine itself purs like a kitten, it runs very nice for an old car, this car has been taken very good care of and runs like a top.
177,000 miles on it.



My thoughts on what it might be?

Radiator

When I replaced the thermostat, there was a little bit of white gunk buildup in the housing. I saw on forums people said sometimes when you see that, it is elsewhere in the system as well, likely in the radiator. The radiator looks like it's the original.

Is there any other methods of checking whether you need a new radiator?


Head Gasket

There is a slight chance of a head gasket. At one single time when it was overheating on a grade, there was white smoke coming out when I turned the car back on after 20 minutes of letting it cool down. That stopped a few minutes later and has never done it again, though when I first start the car up on even the most remote cold days, there is the old car clear-ish smoke coming from the tailpip for a few minutes until it warms up. The smoke is normal smell (not antifreeze or oil) and doesn't appear white like it did that one day though.

Fix the other problem first?
The problem with the restart idle fluctuation, might be related and I could start tackling it one by one?

Other than that, no idea what else to check or ways to check things that I can find, I'm running out of options!

 

It's tough to diagnose and solve problems on a engine that will not hold proper temp. Based on the info given, I think your radiator is garbage. The small tubes that form the core get plugged over time, especially if the cooling system isn't routinely serviced or is poorly serviced. It doesn't take much restriction to greatly reduce the radiator efficiency. Unfortunately this means removing the rad and finding a good radiator shop.

I also think you may well have a small head gasket leak that seals itself up as temperatures rise and the cast iron block expands. I had this very problem in an 86 S-10 with an iron duke 4 cylinder. 5 to 10 minutes of white smoke that disappeared when the engine got warm. One day the head gasket blew out and the head casting cracked. When I pulled the head, I could tell from the corrosion pattern there was a small leak on the cylinder side before the gasket ruptured out the opposite direction. Run a leak down compression test on a cold engine to confirm this.

 

Another thing is, that I'm not loosing coolant at all. Over months I have checked the fluid level and it's exactly the same, so nothing is leaking or burning up, and the tail-pipe smoke does not smell strange, so that smoke is likely something else or nothing at all. That smoke is mostly clear, it looks exactly like when you start a car on a cold morning, except that it happens in weather that isn't exactly cold enough to do that (or maybe I'm wrong), which is why I mention it. It only had white smoke the one single time.

The leak-down test sounds like a good idea.

So far my hunches point to a radiator clog as well. Is there no way to test that out??? Also, I don't think I mentioned before, but I looked down into the radiator when I removed the hoses and it definitely looked like an old radiator, so it's likely the original. I also don't have any paperwork from the previous owner of replacing it, and those records all looked pretty thorough (one owner for the life of the car before me). Though the guy I bought it from (their mechanic), I'm semi-questioning whether he left some paperwork out if he knew there was some problems going on so he could sell it. He bought it from them claiming he was going to fix it up some and then decided to sell it 6 months later. Luckily I bought it cheap, so even if I put a grand into it, I still feel ok with the price I paid for it.

 

Repeatedly getting too hot (sounds like it's been 240+ a lot of times) is a sure way to blow a head gasket if it hasn't yet. You say it never loses coolant, yet it boils over into the overflow? Are you emptying the overflow every time?

Another sign of a blown head gasket is bubbles in the coolant, which will almost immediately push out the overflow (which you mentioned has happened).

I was in denial when my Geo Metro HG blew... https://www.zdriver.com/forums/other...g-metro-29223/

Two things to check:
Coolant at radiator out should see a ~20-40* drop from radiator in / thermostat housing.
Also check your timing. Advanced too far can cause the engine to run hotter.

 

No, it does not get to 240+, it can get up to 240 quickly, but it's only been over 240 TWICE (and did overflow and I replaced the fluid loss). I don't let it get over 240, I don't want to blow my head gasket or overheat my engine!! The problem right now is only that it's running hot a lot more than it should be. It might start overheating now that the weather is getting hotter though, months ago before winter, it was getting up to 240 more than it should have been and I would get nervous and pull over to let it cool down. I will be testing more now with warmer weather, but I didn't get enough time to test before winter came along.

 

170k on that original radiator is a lot bet it needs a new one
i' d have it tested for the combustion gases leaking into the coolant
think I replaced my fan clutch and was fair price.
you can remove the T stat to see how long it takes to heat up .

 

ALL FIXED!!!!! And VERY lucky it wasn't the radiator or head gasket!

It was the fan clutch!

I brought it to my mechanic and one of the guys who works on these all the time said he noticed right away that the amount of air the fan was blowing was less than "normal", so he checked out the fan and said it was a little looser than it should be. He said it wasn't that bad so it was more of a hunch than a sure thing and worth trying, so we went ahead and gave it a shot. And luckily that was it! $180 out the door. It's been running top notch the past few weeks even in this very hot weather. It also just drives better in general, it feels like the engine isn't working so hard or something, or that could just be psychological! :P

Anyway, thought I would post in case someone comes along with the same problem. I love it when people have an actual solution posted! I now have new radiator hoses, radiator fluid, thermostat, and fan cutch, not all too bad on the wallet.

p.s. not sure about the fluctuating idle yet, but it appears that has gone away too. Maybe some kind of vapor lock? If I don't post again, assume I'm not having any problems with that either.

 

UPDATE on this.

After awhile of more driving, the overheating came back. But then I put it into storage for awhile. So didn't drive it much at all. After getting it back out of storage, summer came along and it was still overheating, but not quite as bad. It would really only happen with weather over 80 degrees and driving for more than 30 minutes, or sitting in traffic for 30+ minutes.

Well, the radiator started leaking so bit the bullet and replaced it. It's been quite some time now and zero overheating!! So, it was the radiator, and like the previous post, the fan clutch probably needed to be replaced anyway since it did help for a bit and it had signs of being bad.

There were also no issues with the idle after my last post.

 

Thanks for posting the outcome, dealing with this issue in my new-to-me '86 Z31 and I also suspect the radiator (engine hot, radiator very cold in the middle area, so ...)

 

Actually it is pretty simple. If the radiator is good and the water pump is pumping properly, the thermostat or fan clutch have to be bad for the engine to overheat. Could be the water passages in the engine are clogged, but you don't want to go there.

 

Well, success! I reverse-flushed my radiator for a couple of hours today, with a couple of gallons of Barnacle Buster that I had sitting around from having flushed my 2 V8 Caterpillar 3208 turbodiesel engines in the boat. This bio-degradable liquid, that actually looks a lot like coolant, removes lime, calcium and other deposits from boats' raw water side cooling systems. I figured it should also work on car radiators and because getting the radiator out of a Z31 means removing the front bumper, I thought I would give it a try with the radiator renaining in the car. After fitting two long hoses to the radiator's in and out conndctions, so that I could hook one up to a 12 volt submersible marine sump pump, using the other hose as the return one into the pale with the Barnacle liquid, I got it cranking for a few hours, powered by a spare car battery I have sitting around 'just in case'. Then I purged all the cleaner from the radiator, flushed with clean water, and refilled with coolant taking care to remove any air from the system, I took the car on a 100 mile fast and hot highway run to surprise-visit my son who was studying for a final exam tomorrow. The temperature stayed rock-solid in the middle where before it would start to rather quickly move to the 2/3 mark after maybe 5 miles on the highway.
very satisfying, as the radiator (that I guess is original to the car) gets a new lease on life, I fixed the problem for $0, and I did not have to dismantle the front end. Having a beer now to celebrate.
ps I shot a brief video of the whole setup (bucket, pump, hoses, car) which I will try uploading here or to Youtube and link here.