Overheating problems/symptoms

[Gollum]

Ok, i've been overheating on and off for a while now and I think i'm on the brink of finding the culprit.

 

Symptoms: Start car, everything is fine. I can drive about 5 miles or so with no problems. Temp guage stays bellow half way.

 

Once car starts to get warm the car starts to overheat RAPIDLY. IF I open the hood in a hurry and open the rad cap (with towels ontop of it of course) much air comes out, then maybe a small amount of coolant. Once I put the cap back on the temp goes back down to normal and is stable.

 

The pump pulls from the top right? It seems to me I'm getting air into the system somehow wich means the coolant level is too low to reach the intake hose correct? Could this simply be a bad rad cap? I've never changed it and i've been driving it now for about 1 1/2 years.

 

On a final note I love you hybridz and you guys always seem to be able to make up for my huge ignorance.

[TheNeedForZ]

The pump draws from the bottom of the radiator. After being circulated, the coolant is dumped back into radiator thru the top.

[Gollum]

then why is the thermostat on the top? All the cars i've worked on previously (not a huge variety I should add) draw coolant from the direction that the valve is located to let it in from that location..

 

Hmm, time to take it out and make sure it's functioning and installed correctly then.

[fastzcars]

TheNeedForZ The pump draws from the bottom of the radiator. After being circulated, the coolant is dumped back into radiator thru the top.

Yap thats the way it works. You probably have a bad rad cap, letting air into the system.

[huwwatki]

may be way off but ......

 

mine had a similar poblem just after rebuild.....check your thermostat and housing for any crud that may have blocked it up.....make sure it all clean...although it seems this isn't your issue cause u can 'let it off' check neway....

[iaconsultants]

So do you keep toping off the fluid level on a regular basis. The thing that I noticed that you said is that it stays below half on the temperature side which in cars down here generally means you don't have enough coolant fluid in your radiator and the temperature sensor is not seeing water. If it then suddenly starts to rise in temperature quickly means you have started to biol the fluid and the steam is heating up the temperature sensor. It seems obvious but have you completely topped off your including turning on your heater as high as it can go so that everything is completely full.

 

If you keep the fluid topped off and you keep noticing this heating spike, then you should find a fluid leak somewhere because if the air is out of the system then you should not have any heat spikes. If the thermostat is stuck open then your car should runn cooler than normal. You can check for a stuck open thermostat by starting with a cold car, opening the radiator cap and starting your engine. The fluid stays fairly calm and you don't see the flowing action until the thermostat opens up. So this would be a way you can check if the thermostat is functioning properly without taking it out. If you take it out and want to check it get a cooking pan that is at least twice as deep as your thermostat put water in it bring the water to a boil and drop in the thermostat it will open if it is working correctly.

 

But so far based on what you said it seems you need to top off your radiator and if it keeps needing to be topped off check for water leaks, cracks in the radiator, slight drops of water under the car or wet moist areas along the fluid flow path should show you the problem.

 

Good luck.

[Gollum]

Thanks for the help guys.

 

I just changed the thermostat about a month ago (after overheating problems started) and the area seemed very clean and i'm 90% sure I put it in the same direction as the old one (someone else I know suggested maybe I put it in backwards).

 

I'll do the fluid movement check that iaconsultants mentioned to see if it's showing different states.

 

Is it possible that the only water I'm loosing is from boiling the water and loosing coolant in steam form? Or would that not be able to burn off a quart a week? Becuase I've checked for leaks and can't seem to find any. My only idea is maybe i'm loosing coolant under load, wich I can't simulate with the car sitting wich means I can't look for coolant leaking.

 

Again, thanks for the help. I'm gonna work on it some today and see how it goes.

[TheNeedForZ]

Is the fan working properly? No belt slippage? Is the viscous coupler of the fan still feels very sticky? Did you change the head gasket before having the overheating problem?

[Mr.INSANE]

Is the fan working properly? No belt slippage? Is the viscous coupler of the fan still feels very sticky? Did you change the head gasket before having the overheating problem?

 

That was my other idea might be a bad headgasket

[srgunz]

Not to scare you too much but I would be very concerned about the head gasket. Many times they will leak between one of the cylinders and the adjacent water passage. When this happens you have coolent loss out the tail pipe. That is then replaced by air pressure in the system from the cylinder.

[iaconsultants]

Okay here is the head gasket scare, check, or what ever you want to call it. From all the Z motors I have had apart for water reason, the head gaskets that tended to get water leaks were near the water jacket in the back near number 6 cylinder. What happens you will see a drop in compression if you check that with a gauge from one cylinder to another. The other thing you will notice is that if someone is following you there will be some white smoke coming from your exhaust system which indicates water going into your cylinder chamber and getting blasted out of the exhaust. There has only been one case that I personally have seen that a more forward water jacket has a leak in the head gasket and that is with a warped head. You can check this with a compression gauge also. So with minimal amount of wrenching (pulling spark plugs) you can figure out if you have this issue. Also you would likely find some oil leakage into the coolant that will float up to the radiator cap opening.

 

So hopefully you are not having any of what I just mentioned and if not here are a few things to check.

 

When cold reach under with some paper towel and slip it between the water pump bell and the timing cover on the bottom side. Try to work it inside the bell toward the front of the car. Once you pull it out if you see fluid or a slightly oily coffee color, well then you have a slight leak from the bottom of the weap hole that lets you know when your water pump has gone out. You might have to try this again by starting the car and just letting it run for about a minute and turning it off (then try it a second time). This is a hard leak to detect and it starts out slow and one day when it gets a very good temperature spike it will be pouring out very rapidly.

 

Okay some simpler checks. Look at your heater hoses and where those connections are. If you are running the original cloth wrapped hoses or substandard hoses then you might want to concider replacing them anyway. Usually rubbing a paper towel along those and the joints will reveal if they have a slight leak. You will probably have to do this when it is under pressure though (car hot). Do the same check for the radiator hoses especially theo lower one.

 

If you have eliminated all the above then you should be down to a leak in the radiator somewhere. They can be small and last that way for years. Check your radiator drain plug and make sure that is tight and seals off properly. You could take it out clean it off (and out) and put straight water back in there to test. You can also try what others have tried which are Mothers, and egg (I do not like this one at all), and a few others.

 

Almost forgot checking your radiator cap and over flow. If you have a spare or plan on changing the cap go for it, but if you want to check it to see if it is sealing then you can try this cheesy way. Make a bit thicker gasket ring to place between the cap gasket and the radiator. It is better if you have some kind of compressible rubber you can use but most do not have that laying around so a really cheesy way is some thicker paper or card board. You are not going to leave this there very long so you will not need to worry about it getting into your system. Check to see if your temperature spikes again if so you could probably say that will not be the issue. The over flow line can also be an issue of leaks especially when it gets hot enough to build up steam pockets.

 

From what it seems you have a leak in the radiator (I am guessing based on what you have said) and I think it is either bihind some dirt plugged area in the radiator or near the seam of the headers (radiator end caps).

 

Another thing try putting your fron wheels up (front of car on jack stands) and topping it off that way so you can get all the bubbles and air out of the system.

[Gollum]

Ok, more details.

 

1. The water pump gasket blew a couple months ago so I replaced the pump and gasket then. The overheating problems started after this.

 

2. I'm 99% positive it's not the head gasket. I've dealt with head leaks in the past. The coolant as been 100% clean when drained and same with the oil (changed 350 miles ago).

 

3. When I finished the water pump I decided to not put the fan back on, I'd planned to buy an electric but money has been tight.

 

In theory if it WAS the fact that i'm not running a fan then it should overheat gradually, not quickly wich is the ONLY reason I've come here for help. If the problem had ever seemed like a gradual overheat issue I'd just buy a fan and go from there. I'm having a friend of mine (who owns a shop) order me a universal 10" electrical fan monday (i'm going to do some more research here on HZ and see what other people are running). So i'll be able to pick that up teusday and install it. Hopefull if I'm really luck that will be the only issue. I might also pickup a new radiator cap while I'm out since they're not very expensive.

 

Now, in the 3 times i've flushed the fluid I havn't jacked the car up to release air from the system. My driveway however is at about a 40-45 degree angle. Would this be sufficiant? I don't remember ever running it with the cap off while it was in the driveway so that's a possability.

 

On a final note there is the standard white exhaust in the morning while the car is cold (doesn't smell of coolant at ALL) then once the car is warm there is no visible smoke.

 

I just need to avoid all this drama and find me a L28et

[Guest 280ss1976]

well i know every o0n telling u to drain and refilll try cleaning it this way take the hose and on the top rad hose stick it in and let it flush the system out the disconnected bottom hose and leave the drain plug and flush the radiator till it clear i kept over heating till i did this sometime not big trash but lil stuff tat makes a difference adn try a fail safe thermnostat might cost a lil more but there no excuse for fluid not to move as far as electric fan i seen some work and some not all depends make sure the elctric shroud is on the rad and put hand behind to see if sufficient air is coming through might be due to lack of air also u could be over filling the rad empty the over flow bottle before refilling try to do on a flat surface if this dont work then i cant say what it be i lean towards checking water pump and even rad might be bad if not that then got to the head gasket but 90% of the time on the head gasket deal watch your oil it look muddy looking means water mixing in it hope this help but it the steps i took till i got aggreavated and throwed a 350 in mine

[Guest Sleepy-z]

I say take it to a Z meet tommorow if you can and let some friends look at it;)...not emplying me, but there are a few other old Z's coming that might have a idea.....still going to jelly belly afterwards as planned, I will call around 10-11 tommorow and see how your doing and hopefully you will make it with the 280zx.

[TheNeedForZ]

Dude, signature size limit....nice pic tho.

[TheNeedForZ]

That was my other idea might be a bad headgasket

 

I asked about the gasket but I wasn't wondering about a bad gasket, but rather a "wrong" one. The F54 block requires a head gasket unique to its own. The F54 head gasket blocks a water passage to re-distribute coolant flow. But since the problem started after a water pump change followed by FAN REMOVAL then we'll start from there.

 

3. When I finished the water pump I decided to not put the fan back on' date=' I'd planned to buy an electric but money has been tight.

 

In theory if it WAS the fact that i'm not running a fan then it should overheat gradually, not quickly wich is the ONLY reason I've come here for help. If the problem had ever seemed like a gradual overheat issue I'd just buy a fan and go from there[/quote']

 

So all this time you are talking about a fan-less engine that overheats?

 

I learned a saying from the movie "An Inconvenient Truth", I believe the saying was by Mark Twain "It's not what we don't know that gets us into trouble; It's what we know for sure that just ain't so." If a car requires a fan to cool normally, what is going to happen when the fan is gone? It's more than logical to relate the overheat to the fact that the fan is removed because the fan cools the radiator, and the problem started after you removed the fan. The radiator only "radiates" a limited amount of heat away, the majority of the cooling effect depends on the cooler airflow passing thru it.

 

Put the fan back on you FRIGGIN MANIAC:biggrin:

[Gollum]

Point taken for sure needforz, but it just seems odd to me that I can go from 1/4 temp on my guage to 3/4 temp in less than 20 seconds... doesn't that seem odd?

 

Many times it overheats seemingly far too quickly to be fan related. I don't think a fan will magically cause the cooling system to work 1,000% better.

 

But hey, I'll admit to the maniac part

 

As stated before i'll order one monday. today and tomarrow the schedules too tight to put it back on and I wouldn't want to put it back on just to take it odd again teusday.

[TheNeedForZ]

Point taken for sure needforz' date=' but it just seems odd to me that I can go from 1/4 temp on my guage to 3/4 temp in less than 20 seconds... doesn't that seem odd?

 

Many times it overheats seemingly far too quickly to be fan related. I don't think a fan will magically cause the cooling system to work 1,000% better.

[/quote']

 

Let me see if I can figure this out...

The Z car holds a bit less than 3 gallons of coolant(10.3liters says Haynes manual that's 2.7 or so gallons), but how fast does it circulate? Well for a lack of data I'll use that of a SBC pump. Assume the L water pump is similar to the SBC pump in terms of size and drive speed, it'll circulate roughly 9 gallons per minute AT IDLE RPM(800). So the coolant circulates the whole system every 20 secs at idle. That means the already hot coolant passes thru water temp sensor, goes to radiator(without dropping much heat), comes back into engine, absorbs heat again, passes thru water temp sensor again in about 20 secs. That should explain why the temp raise so fast.

 

But why does the engine overheat as soon as it warms up? Well in the beginning, the thermostat is closed, forbidding coolant circulation before the engine warms up. Once the engine(coolant temp) is warm, the thermostat opens to allow coolant circulation : the warm coolant leaves engine, goes to radiator(without dumping much heat), comes back into the engine and picks up heat again, flows thru water temp sensor....all in about 20 secs. This explains why your engine will overheat very quickly after it warms up. Hope this helps.

[Gollum]

Hmm, makes sence. Although it doesn't answer ONE question I have that I think is odd.

 

Usually temps will go down to normal once i'm driving a good speed (once air is flowing obviously), but sometimes even at freeway speeds it's not enough too cool the car down.

 

I was under the assumption that at freeway speeds a fan is basically useless since it won't create airflow moving faster than the 60+ mph wind being generated. Am I wrong? (don't be afaid to say i'm wrong, admitting your wrong is the first step to learning something, and I really am seeking to lear something here)

[TheNeedForZ]

Great question, I have no idea why. Maybe your car is a female and she's punishing you for leaving the gas door flap open....5 months ago

 

I can't even tell how much air can pass thru a S30's radiator at cruise without the aid of a fan, not to mention a ZX which is what you have IIRC. IMHO the large radiator opening on S30 might allow it to cool unaided at higher speed, but a ZX is altogether more aerodynamic with smaller frontal opening and a integrated G-nose feature. I suspect there is lesser air that can pass thru the ZX rad opening unaided at the same speed.

 

Perhaps the direction of wind plays a role. When you travel against wind, the wind-to-car speed is more than 60, so you pick up some good cooling. When you travel with the wind, the relative wind speed is less than 60, less air pass thru the rad, less cooling. If you were travelling slightly uphill then the engine requires a heavier load to maintain the same speed and generates more heat. If you cruise with top gear then the water pump is driven at a low speed which leads to slow circulation and higher temp.....etc etc.