rough idle when hot

[oldhemi]

Beandip is one of "da mans" that I follow on Z's. He should have some good input here. From what I have read, there is some sort of nozzle in the hard line in the return. It is some sort of metering deal. I dont have the hard lines anymore, so I cant help there. It is sounding a little like fuel "boiling".

Good tip on the wp bolts. Maybe some neversize on the new ones? I hope that you can remove them w/o breaking them. I have a spare L28 sitting here with a broken wp bolt and some sort of silver colored goop that matched the aluminum color so well that I never noticed the broken bolt when I picked the engine up!

My Z blew a head gasket on cylinder 5 back in '86 or so. Symptoms were running like it was on 4-5 cylinders at times and then clearing up at other times. I can not remember if it was worse at low speed and idle or not. I am pretty sure that my temp gauge was running hotter also. I had a friend who worked on Z's part time and had done many headgaskets. He listened to my description of my problem on the phone and immediately stated "headgasket". He came over that weekend with the tool - wooden stake - to hold the cam chain tensioner in place and we were done real quick. It helps when you have an expert make a house call. I digress.

If its idling for 3 minutes and getting hot, you could wait to see if your thermostat kicks in and its starts cooling down w/o driving the car - if it keeps getting hotter it could be the thermostat - or not.

Open the hood and put a box fan in front of your radiator and see if this environment keeps the car cool. If so, its probably not your head gasket and more likely a fuel issue. Hopefully someone can chime in if this is a valid test.

I agree with your plan to do the thermostat 1st. As least check it like Beandip outlines and you can also see what temp its rated at.

Here is a tip - do not use the wife's best pot or her candy thermometer. Even with her permission, it can be a sly trick to get new pots and pans! Even a cheap electric frying pan even has a temp gauge built in!

[steve91tt]

Update:

I installed a new thermostat, water pump, rad and heater hoses. I also added a MSA fan shroud.

Observations:

1. The fan shroud is a bit more of a challenge to install than I thought it would be. It did not fit as shipped but with a little modification all is well. Here is a link to a good post on the topic. http://www.classiczcars.com/forums/showthread.php?t=30889&highlight=shroud+fit

2. The old thermostat was a 160F unit. I replaced it with a 180F unit. I tested both side by side in hot water and both opened when they should.

3. The old water pump looked good inside and out. However, the impeller on the new pump was iron where the old pump was aluminum. I'm not sure if it matters.:paranoid: The old pump was stamped "AC delco"

4. I dunked a magnet in the old coolant and found a couple of grams of metal shavings. I'm not sure where these came from as the old water pump showed no signs of wear.

5. The car runs fine. No leaks. The temperature gauge runs a little higher than it used to. About a needle width past half where the old thermostat would run about a needle width below half. I ran it around town and let it idle for 10 minutes. No overheating. However, it's only about 55F here today so the real test will have to wait for the sun to come out.

[steve91tt]

Well, that didn't seem to fix the issue.

It's 70F today. If I drive for a couple of blocks I get a solid 700 RPM idle and the gauge sits a little over half way. However, after a few minutes idling the gauge goes to about 3/4 and the engine starts to cut out. It will even stall if I don't give it gas.

I'm going to take apart the fuel system tonight to trouble shoot that end but I'm pretty sure I still have a cooling issue. New rad, pump, thermostat, hoses, fan, clutch, shroud...What's left?:disappoin

[steve91tt]

Could I have a coolant line routing issue? The PO made a few "modifications" to the routing. He capped off the line at the back of the engine on the spark plug side...

And he capped off all of the water lines on the intake side.

Does this look right?

[steve91tt]

I dropped the tank tonight and found more gunk in the tank than I had expected. The inside surface looks 99% good but there are a few rust spots which I assume is the source of the black bits floating in the bottom of the tank. I have a can of POR15 on order so hopefully after I coat the tank and replace the filters my fuel problem will be solved. Fingers crossed.:classic:

[Pomorza]

The coolant lines on picture one are rather odd in my book. I would take them all out and go back to the standard way it should be. (which on my 280 is the lower hose attaches to the water inlet and then to the lower heater core hose. Then from the lower heater core hose it will go into the engine block via the rear intake) As for the second pictures. I'm not a 240z guy (nor expert in any means) but I believe that is either the outlet for the coolant lines that run through the intake or its for somekind of sensor. I'm not 100% positive on which one as I own a 280.

Hope that helps.

Jan

[Curtis240Z]

The coolant blockoff looks okay on the intake side for a 240Z. Did you check to see what Beandip previously mentioned regarding the metered orifice on the metal return line above the mechanical fuel pump? I would also open the gas cap and carefully apply air pressure to the return line going back to the gas tank to verify it isn't plugged.

[steve91tt]

Did you check to see what Beandip previously mentioned regarding the metered orifice on the metal return line above the mechanical fuel pump?

I plan to take all the lines and filters off and blow them down or replace as necessary while I wait for the POR15 to get here. Before I removed the tank I confirmed that I have return flow by pulling the return line from the tank and running it into a gas can. With the ignition on (car not started) fuel trickled from the return so I know the electric pump is working and the return system is not 100% blocked.

[steve91tt]

the lower hose attaches to the water inlet and then to the lower heater core hose. Then from the lower heater core hose it will go into the engine block via the rear intake)

Jan, thanks for the feedback. I believe that my system is plumbed the way you describe and the way it is described in previous posts(sorry for the poor photo).

The flow comes out of the rad where it forks. Part of the flow goes to the block in the front of the engine and part goes to the upper heater hose. It comes back from the heater and into an inlet in the back of the block.

[oldhemi]

I think I know where you are HEADing on the cooling issue. You have attacked all of the smaller items on overheating problems - and more with the radiator shroud!

Since you have tested the car with more than 1/2 tank of gas, you probably have ruled out the pick up tube being perforated. Because the tube bottom sits off of the bottom of the tank, its doubtful that some rust will be a problem. Plus you have a filter between the tank and the electric fuel pump. I have never checked the return line's output, so I have no knowledge on how much of a spray should be coming out of there. Hopefully someone will chime in about that.

I admire your "get r done" attitude and the quickness in all of this work. I have a Slant pressure tester if you wish to borrow it. It will tell you if you have a compression leak. I live on the north side - 249 and Louetta. Its about 4 miles north of the 1960/249 intersection.

PM me if you want my phone number.

[steve91tt]

I have a Slant pressure tester if you wish to borrow it. It will tell you if you have a compression leak.

Oldhemi, I very much appreciate your offer and I might just take you up on it. The car is up on jack stands at the moment and the fuel system is in pieces. I will be trouble shooting this weekend and coating the tank. If all goes well I hope to have it together for the next round of testing next weekend.

I plan to use an IR thermometer to track where the heat is going in the cooling system and use that data to figure out where to look next.

[oldhemi]

An IR might be helpful! I also have one of those. IIRC, aim it below the spark plugs at the gasket for variables comparison. #5 is the troublesome booger.

Good luck on the tank job!