# Overheating issues after replacing head cylinder - 4X4 86.5 P/U



## hnic17 (Jan 29, 2008)

The following facts may be relevant:

- 2 weeks ago the water pump failed and I blew a head gasket. Since then I took the head off, replaced the gasket, had the head milled, and replaced the gasket.

- In the course of things I decided to replace my thermostat. Much to my surprise, there was no thermostat present in the intake! (I now assume this accounted for the perpetually low engine temperature before the head gasket failure). Not to be deterred, I installed a thermostat, since I reasoned that $4.50 is a small price to pay for proper cooling and heating of my engine.

- Once everything was put back together, I filled the radiator with coolant until it wouldn't take any more. This was approximately 4 quarts. I then started the engine and everything seemed fine. There was no more coolant blowing out of the intake, no bright white smoke coming out of the exhaust, and therefore I determined that the head gasket replacement was a success. HOWEVER --

- After the engine had been idling for 5-6 minutes, the engine began to overheat. This is odd, since it seemed to be idling for those 5-6 minutes without the gauge showing any sign of temperature increase. Then the temperature began to rise at a *very* steady rate. It was also during this time that I had the heater on full blast in order to see if it worked. It never did. Even when the gauge showed the engine temperature to be just below the highest acceptable mark, the air coming out of the heater was the same temperature as the air outside. After turning the engine off, I checked the radiator (did not take the cap off), and the entire radiator seemed to be completely cold, leading me to be believe that it was either empty, or that it was simply not circulating. The other interesting fact is that the seal where the thermostat was, was giving off a tiny amount of smoke or steam. I also noticed that my idle RPM was steadily increasing as the engine began to warm up, but decreased when it got to a certain temperature, and I turned the heater off. By increase, I mean a notable increase of around 400 RPM. --- This is my dilemma.

My ideas are as follows:

- First: Is it possible that the coolant just wasn't circulating? That perhaps the thermostat wasn't opening for some reason? I assume that the mechanic who owned the truck before me would have installed a thermostat (due to its ease and cheap cost), unless there was some compelling reason not to. I did not have time to take the thermostat out and retry, since the engine had to cool first. Also: perhaps it was human error. Perhaps I installed the thermostat incorrectly. (I installed it with the flat side pointing toward the radiator hose).

- Second: I find the fact that the heater did not work troubling. If the engine was that hot, shouldn't the heater have been fine? It is my intuition to take this as a clear sign that the coolant was not circulating. The heater pump sounded labored as well. Is this explained as well by improper circulation of coolant? Could the fact that the heater was on but not working account for the engine overheating? Again, I am not sure whether the two exactly coincided, but I think that they may in fact be causally linked.

- Third: Is it possible that I just need to put more coolant in, since it could have circulated through and there was just not enough to keep the engine cool? I realize this is probably a stretch.


Any diagnostic help would be greatly appreciated, as the novelty of endless tinkering on my daily driver is starting to wear off....


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## hnic17 (Jan 29, 2008)

*BY THE WAY.....*

Also something to note... the vacuum tubes are all disconnected, and have been so since the mechanic that owned it took them off. He said it ran a lot better without them. Indeed, I never had a problem before the head gasket deal. so... perhaps it is irrelevant. I don't know...


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## OchnofConcrete (Jan 7, 2008)

check for a air bleeder screw for the coolant system.. probably still have air in there keeping the thermostat from working. unless somehow you didn't read up enough info on the head gasket and somehowyou should have opened up a coolant passage. that's gonna be hard info to find. but when i switched out my thermastat, same thing happened.. just still had air in system.

4 qts to me seems a little quantity.. i don't drive a truck, i drive a sports car and my takes if i remember correctly 6.3 qts. 

helps to squeeze repeatedly and move around the radiator hose so it move the fluid into the engine.. and also leave the bleeder screw off while doing this so the air will be able to escape. rotating the engine helps but by turning it on you did that.

you said you replaced the water pump... didyou put excess sealant on the mating surface???
maybe it needs a flush because when you changed the head gasket, you didn't pull the block to use a screw driver to knock around and scrape out the old gunk in there. maybe radiator's clogged. 

here's the thing.. it overheats when coolant doesn't pass through the engine quick enough or not at all... only things that cause that are inoperative thermostat *which may be why they took it out*, gummed up waterpump or busted waterpump, a headgasket that wasn't correctly made and is cutting off passage needed, or a gummed up radiator, or in the worse-case scenerio... a gummed up engine coolant passage not allowing coolant through.


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## OchnofConcrete (Jan 7, 2008)

or a clogged heater or AC.


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## smj999smj (Jan 1, 2006)

Would be nice to know what engine we are working with....It sounds like a Z24i by your description. I always stress the importance of using an original Nissan thermostat to people. Since you say it cost $4.50, it sounds like you have an aftermarket (Nissan t-stats usually run around $17). With aftermarket 'stats, it's usually a good idea to drill a 1/16" hole in them and locate that hole towards the top when installing to help air purge out of the system. There's a good chane that there is air in the system. You should not install the cap until the air is purged out and coolant topped off. Raising the front of the vehicle will help purge out the air. Was the head checked for cracks? Did you have the radiator flow tested? Are the core fins in good shape on the radiator and AC condensor to allow for good airflow through them? I don't believe this engine had a "bleed screw." The VG30i had one at the top radiator hose and the later KA24E had one, but I don't recall one on the Z24i...


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## hnic17 (Jan 29, 2008)

*PROBLEM SOLVED - one more question though...*

Sorry about the lack of engine info. It's a z24(i). 

I fixed the problem. I hedged my efforts to make sure something worked. First I unplugged the heater hoses, ran a garden hose through the heater to make sure it wasn't clogged, and to flush it out. It wasn't clogged at all, so that wasn't a big deal. I took out the thermostat and confirmed its functionality in a pot of boiling water. Then I reinstalled the thermostat, but not before pouring coolant directly into the space behind it in the intake, until it was about to overflow, so as to prime the thermostat so to speak. Then I topped off the radiator and started the engine without the cap on. I squeezed the hoses and heard gurgling every once in a while. The coolant started working once the gauge was a bit over 1/3 of the way across from the left. The heat works fine now.

I now have a non-serious question concerning the thermostat itself. In reinstalling it, I noticed in the factory manual that a 95 degree Celsius (203 degree Fahrenheit) thermostat is called for. This thermostat that I installed was 180 degrees, a 23 degree difference. I assume that this is the cause of the early release of the coolant. By early release, I mean that most properly functioning cars seem to have their temp gauge needle hovering just right of the mid-point, but this one, even after driving 20 minutes, was still at about the 1/3 point from the left. The question is, should I obtain a thermostat which opens at 203 degrees Fahrenheit? I know that every engine has an optimal temperature to preserve the ideal fuel economy, something that is rather lacking in my truck. If I were to install such a factory spec thermostat, would there be a noticeable difference in said fuel economy? Or should I just be happy with what I've got?

Thank you everyone for the help!


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## OchnofConcrete (Jan 7, 2008)

smj999smj said:


> Raising the front of the vehicle will help purge out the air. Was the head checked for cracks? Did you have the radiator flow tested? Are the core fins in good shape on the radiator and AC condensor to allow for good airflow through them? QUOTE]
> 
> forgot about that... had to jack up the front of mine to help it along, after that it was fine.


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## OchnofConcrete (Jan 7, 2008)

uhh... i can't recall if i've ever heard of coolant helping fuel efficiency. if i remember correctly the thermastat temp is more for what type of climate you're in or how hot your engine runs if it's modified. if you're in a warmer climate you get one that keeps the engine cooler, in a colder climate you get one that keeps it warmer. if in a normal climate, i'd get one that keeps it cooler just so it's easier on the engine. at least i'm pretty sure that's why... i used to know but trying to recall *bad memory* ;]


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## smj999smj (Jan 1, 2006)

My recommendation is a genuine Nissan thermostat, P/N: 21200-80W00


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## sharpeusn (May 9, 2007)

*Over Heating? Answer!*

I had this ame problem many times until I finally learned the solution after having to replace my head gasket 3 times! OK here goes this is a very easy and free fix. The Nissan HB truck engines are actually designed differently than most others. I am assuming you have the Z24i but it really doesnt matter which one you have. The cooling systems flow backwards from other US and some Japanese vehicles, in order to relieve your cooling problem heres what you have to do. When you removed the head and thermostat and all those goodies you created an air pocket which sorrowful to say is a HUGE problem in Nissan HB's. You can either A: Massage yes I said Massage the upper radiator hose while the truck is running in order to force the air bubble out of the system, you will want the radiator cap off for this one. OR B: there is a "vapor or steam release valve" on top of the intake, it has a ALAN or HEX pattern to it it should be fairly easy to get to if you have your air cleaner off. Opening this while the engine is running will allow the steam and air bubble to release. Happy Truckin'


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## scout (Aug 24, 2007)

there is a "vapor or steam release valve" on top of the intake, it has a ALAN or HEX pattern to it it should be fairly easy to get to if you have your air cleaner off. Opening this while the engine is running will allow the steam and air bubble to release. Happy Truckin'[/QUOTE]

Could you give me a few more clues where to find this steam release valve. I just went out to the garage and looked at my 89 z24 intake manifold on the bench and located several hex plugs but I'm not sure that they are what I expected. One is under the pcv and the other two are on the back side of the intake manifold. All three look more like plugs for unused holes rather than valves. Also they are horizontal rather than vertical.
Thanks.


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## OchnofConcrete (Jan 7, 2008)

it's somewhat easy to find if you keep in mind what it's for man....

just follow the coolant passage on the intake manifold.. you know that extra port on the manifold, that'f for coolant... 
((( usually this is the highest point in the coolant system overall. )))

on mine, it's directly after where the upper radiator hose connects onto the intake manifold. but it may further along the coolant passages on yours.. just keep in mind... where your radiator hoses enter the engine.

you have one that goes to the top and pours coolant onto the water pump pulling the coolant to it.
then you have a return line at the bottom of the engine (on mine) that returns the coolant after it's circulated through the engine. my heater and intake hookups for the coolant are seperate hoses that are coming off close by where the coolant goes through the intake manifold. but here's the thing... it doesn't have to do that if your car is different. the intake doesn't really need to be cooled. it's just a compact way of getting the coolant to the water pump/heater/intake collector... dunno, just keep in mind your two main large radiator hoses.. the one going to the pump, and the one returning to the radiator.

if you look where they enter and exit, you should be able to find the rest of the coolant system... anything that is connected to where those hoses enter/exit will have coolant inside it.. and it tied in with the system... given chance for air to be in there if you don't have enough coolant in there instead of air. somewhere along those routes (most likely the highest point available, and if your car isn't a foriegn whore.... ;] ...the air bleed screw is most likely close by the upper radiator hose. or along that route. 

sides that... if you can't find it, don't have one, you'll have to run the engine with the radiator cap off. but i'm sure there's gotta be an air bleed bolt. it's usually small.. mine's a 10mm. 

just keep massaging your upper radiator hose to slosh the coolant around. that'll get the air to the "top" of the system and out that bleeder hole. any smaller air pockets will eventually get pushed to the radiator... i think. i've heard some horror stories about certain cars having probs with you doing anything yourself, without some sort of flushing system that doesn't allow air intothe system.. but when you start thinking about it... "how the hell do you work on this car without effing it up? freakin engineers were high that day."


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## sneakboxer (Jan 12, 2008)

Food for thought... When i change a thermostat in any water cooled engine i make sure that the jiggle valve (a barbell looking thing on the thermostat) is on top. Or if the thermostat does not have a jiggle valve i drill a small hole(1/16in) where the air can bleed off. 
I also do the masage thing and i only run the engine a few min at a time to ensure i don't cause any hot spots in the head. If you let the engine sit a wile it should draw water in to the system from the expantion tank. 
Take your time and make sure you have all the water back in the engine prior to loading the engine or bad things may happen.


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## smj999smj (Jan 1, 2006)

Z24i's don't have air bleed screws; KA24 engines do.


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## scout (Aug 24, 2007)

*Thanks*



smj999smj said:


> Z24i's don't have air bleed screws; KA24 engines do.


Thanks. It is tough enough to see something wearing bifocals. It is even tougher when it does not exist on my Z24i.


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## sharpeusn (May 9, 2007)

No problem keep us updated on how everything goes.


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## Copper93 (Mar 24, 2007)

I don't know about Nissans but on other engines the gaskets have two sides. They both look alike but the water passages are slightly off. If you put it in upside down it will block the passages and reduce water flow. That will cause your overheating problems.


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## OchnofConcrete (Jan 7, 2008)

i'm glad someone knew to clear that up for you.  all i really know is my engine and a the basics on others. you talk about the KADE, and i can go on all day about the stuff you need to know. 
if you don have that bleed screw like he said, i'd keep the rad. cap off, massage uppper/whatever hose that leads coolant to the water pump... probably even hook up a hose to get as much air out of system as possible.
that's why it's worth it to just go to a lube/whatever shop and just get a rad. flush... only new fluid... hopefully, and hopefully the kind you want (i always just throw in Prestone 50/50... it's cheap and good)...sides that keep turnin it on and off trying to move the air out. (jackin the front up to angle air bubbles towards radiator cap hole)

hell man... tap a freakin bleed hole yourself... ya know... that's easies stuff, and it's your coolant... a lil metal shavings will not only come out in a flush but will also not mess up anything. still want coolant in there, so get em out.

the drilling a hole in the thermastat is jut a way of creating more flow. that's what the thing is for... keeps a valve right before the coolant is loaded onto the waterpump. lets the right amount through... think of this...
coolant moves through system to cool, but even that stuff will heat up if it's let to move too fast... but with a thermastat, it lets the right amount through and drilling a hole would help cool rather than add too much friction in the coolant. so... i might seriously think about doing that myself next project. just got that dam seal time afterwards if you have to seal your therma. 12 hours minimum... recomend 24.


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## paulsurfer (Aug 30, 2006)

when you turn the engine on to pump coolant through everything, turn on the heater to full blast and high heat. Only run the engine for a couple of minutes at a time tops.


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## hnic17 (Jan 29, 2008)

*temperature say what? wtftkd!*

so. The head gasket swap hath worked magik on my engine it appears, and thx to advice from many wise elders of this forum, the coolant circulation problem seems to have been solved. Now there be yet another question, and since I am still a n00b at this and am far too busy with impractical shite like law school, and I am wondering what I can do to remedy the situation.

It appears that my old friend the temperature gauge is being irrational. Sometimes the gauge will work for all or part of a drive, but usually it just stays down to the left as if the truck is and totally cool. Yet I know it is not cool, and therefore get nervous when I cannot monitor the temperature. So, the query is what may be causing the temperature gauge to be temperamental? (no pun intended).

Also if I may steal some more time away from those of you at work, I changed the brake calipers and the pads recently, and bought the rotors to change (since one the old ones had two cracks running up the side and had worn dangerously thin). But I could not change the rotors myself, or rather, I totally cowered in fear of doing it, b/c I heard that bearing would roll out when I took the rotors off (this being a 4x4 truck). This unpleasant experience kept me from doing further damage than was contemplated. Should I do them myself, or take it to a repair shop and give them the parts? Also, how the hell do I take off the rotors anyway? I suspect i remove the lockout caps first, but do i then a special tool?


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