240z overheating at idle in traffic lights and intersections

[Jarvo2]

Great suggestion, just added it and several others from my collection.

[Namerow]

Carburetors have their charm, but after reading through this Nissan, 'how-to-make-it-run-sort-of-ok' document, it's easy to see why the industry embraced electronically-controlled fuel injection when it was finally ready for prime time.  Of course, if there were no emissions control requirements and no CAFE rules and we all lived in San Diego, carburetors would probably still rule.

 

[jalexquijano]

Namerow,

One friend of mine has an additional Manifold Heat Control Thermostat which he confirms its working. So i will have the radiator flushed and fully inspected, swap this thermostat and test the car. I will not get into removing the freeze plugs in the engine block until this is completely verified. I will also have a vaccuum test done to the car.

Edited January 13, 2016 by jalexquijano

[Stanley]

You could also test the manifold heat control thermostat you have now. It looks shiny and fairly new. Maybe the previous owner bought a new one and installed it. They were available until a few years ago. Your car's symptoms aren't related to the cooling system, and the temperature readings you got with the IR gun were normal, but it doesn't hurt anything to clean it all out. I thought they always cleaned out (hot-tanked) the block when rebuilding an engine, but maybe not. When my father-in-law helped me rebuild the engine in an old Chevy, under the shade tree years ago, we didn't bother with that.

You could do a DIY flush. Buy some radiator flush liquid, put it in according to the instructions, and drive it on the highway for a hour or so. Then drain the radiator into a container while it's still hot. If the old coolant comes out looking gunked up, then repeat the DIY flush or take it in for a major flush. Otherwise, you can forget about it.

[Zed Head]

Blocking the heater hoses and the manifold line would answer some questions.  Super easy.  No down side, in Panama when it's 80 degrees outside.

[jalexquijano]

Car overheats and stalls at traffic jams and intersection but not while parked under shade!!

[Zed Head]

Exactly!

[jalexquijano]

Flush was done. The problem is not the radiator!! Mechanic says Radiator is perfect no need to fix or change (Charge 3 dollars for inspection). It could be either the manifold heat control thermostat or something else. When returning from the Radiator Shop the car temperature reached to a Little less than 3/4 of the gauge (I installed a Brand new OEM NISSAN 170° F thermostat before turning the engine on). The idle became rough and the car stalled a couple of times during traffic. Got home pulled all the plugs out and the were black. I guess the car overheats and this causes the plugs to become black which eventually turns the idle rough concluding with stalling. I can lower the mixture and set the timing to 10BTDC at idle but this will cause backfire at the intake and loose of power.

Should i do leak down test? A vacuum test? or should i wait until i receive the manifold heat control thermostat and install it? Guessing is not solving anything.

 

Edited January 15, 2016 by jalexquijano

[Zed Head]

jxq must have me on Ignore User.

[siteunseen]

"guessing isn't solving anything" we've been telling you that for two years. 

I guess you're not taking our help seriously.

[Stanley]

Right !  No Guessing !  Leave the guessing to the experts.  You aimed the new IR gun at the radiator and got 185F when the gauge showed 3/4, correct ? So that's OK. Overheating won't turn the plugs black. Maybe the gauge or sender is bad. Changing gauge is a hassle, but changing sender is easy.

I have a few questions:

1. Do you have a digital copy of the FSM ? Blue uploaded it a couple months ago, it's all divided into sections so you can find the section with the carb tuning and print it, or put it on a flashdrive, and take it to the printer. You can't tune the carbs without instructions. There are other instructions, but FSM is almost complete and easy. You need to follow it exactly, and you have to have it printed so you can put it on the fender and refer to it while you're doing the tune-up.

2. Do you have a uni-sen or synchrometer ? You can't tune the carbs without one or the other (unless you're a expert with SU carbs). I prefer synchrometer, because it has numbers that you can write down for reference. FSM explains how to use it. It's almost fun. MSA sells both.

You need to raise the nozzles to lean the mix, not lower them.

When the mix is set according to FSM, you can fine-tune it with street tests. The IR gun is also useful to see that all cylinders are getting the same air/fuel mix. I point it at the same area near each spark plug, and write down the temp. Then do it again and average the readings for each combustion chamber. The gun needs to cool down about a minute between each reading. If the front 3 are hotter than the back 3, then the front carb is set leaner than the back carb. It's fun to watch the temperature readings change when you make a small adjustment of the mix nuts.

Now I have a question for the experts. Could a bad vacuum advance cause the change in RPM at idle ? I suspect a combination of problems.

[psdenno]

2 hours ago, jalexquijano said:

Flush was done. The problem is not the radiator!! Mechanic says Radiator is perfect no need to fix or change (Charge 3 dollars for inspection). 

 

 

Interesting.  I told you the radiator was fine and not the cause for your problem on January 4th.  Could have saved $3 and 10 days by listening.  My point is that you've received wonderful advice from experienced Z owners and ignored it.  Stanley's post above is another example of great advice.  A Uni-syn, or similar carb tool, to synchronize the carbs is essential.  Guessing won't do it.  

Dennis