240z overheating at idle in traffic lights and intersections

[jalexquijano]

On ‎01‎/‎05‎/‎2016 at 1:28 PM, Zed Head said:

This is good information.  Another clue would be what the temperature gauge does while these things happen.  Even though they're not accurate, they're still good indicators.  Where is the needle when you're "running the car" and where is it when you're "stuck in traffic"?  If it's in the same spot, then the cooling system is working.  Engine temperature is not changing between driving and stopped.  But engine bay temperature might be. What thermostat temperature are you using? Maybe you just need to use the 160 and you have a 180.

Here's a question for the carb guys - would measuring fuel flow on the return line be worthwhile?  I don't see it in his pictures but I don't really know what I'm looking at.  Could be that his guy is running it dead-head style and the insulation is being overpowered at a stop, or he just has low flow for other reasons.  If I had carbs I'd probably use that as an overall check of the lines and fllters.  Without good fuel flow past the carbs vapor-lock could still be a problem.

 

Also - I attached a picture of what looks like a hose laying on your throttle linkage.  Could cause throttle feel issues.   

I moved the fuel lines further back so it does not make any contact with the linkage!

[jalexquijano]

23 hours ago, Zed Head said:

So you do have a small amount of heat buildup.  Still doesn't really explain your problem, but might be a factor.  

Here's something easy to look at that might be significant, especially since you're in Panama and probably don't use your heater - are the heater core coolant lines from the back of the head blocked off or are they looped back to the water pump, from the head?  Or are they connected properly to the heater core?  Looping the line back to the pump inlet (bypassing the heater core) can cause overheating, in a perfectly fine cooling system.

 

And, still wondering about fuel pressure, and the return lines for your fuel supply system.  Important.

Mechanic came yesterday. We tested the car!! No backfire either on intake or exhaust. Car ran fine. When parking the car after waiting 15 minutes at idle, RPM started to drop from 1000 to 800 and raised again. We even took the thermostat out, He ruled that the problem was the radiator and i needed to take the car to a rad shop for flushing and cleaning. If this did not solve the problem, he will need to remove both lids shown on picture 2 and do a complete cleaning removing any rust inside the wáter channels. By the way who sells these lids? How are they called?

 

Anyone here has a different approach to the solution he has offered?

[Jarvo2]

Have you guys tried blowing out the fuel return line with compressed air?  Gotta keep the fuel circulating to prevent vaporlock.

[Zed Head]

On 1/5/2016 at 0:08 PM, jalexquijano said:

while running the car the temperature gauge needle sits in the middle. Once stuck in traffic or at a parking it starts moving to 3/4.

It must be tough down there to find someone who knows these cars.  You said that the radiator works fine "while running the car".  And overheating when stopped is more likely to be an air flow issue. 

But I do see that you have the coolant hose looped back to the water pump inlet.  This will allow the coolant to flow back to the pump without passing through the head or through the radiator.  Try blocking that path before doing anything.  No guarantees but it's cheap and easy and will help cooling. 

 

[Zed Head]

Also, it may be that the way you have those hoses connected runs the hot water through the carburetor heating plates.  I think that there's supposed to be another thermostat in that line to the carbs, but don't really know the system.  But, being in Panama, I think that you could block both of those lines and improve cooling for the engine and avoid overheating the carbs.  That might be the whole problem right there, you're overheating the carburetors.

Hopefully one of the carb experts will chime in.  If I'm off-base feel free to send a torpedo.

[Jarvo2]

Agreed.  

 

[Zed Head]

Tried to find more on the topic and went in a big circle back to myself (!) and others.  It's down near the bottom of the page (this is why we need post numbers Mike).

 

 

And here's the picture and description from the FSM.  I would check for that thermostat first, and block the line at the back of the cylinder head.  That should give proper flow and control, for cooling and carbs.

 

 

[Stanley]

It's very easy to test for plugged radiator, as posted previously. But you tested it yourself, saying temp was normal running on the road. If the radiator is badly plugged, how could it possibly run at normal temperature on the road, on a warm day? Besides, 185F is normal. Sounds like your thermostat, water pump, and radiator are fine.

Blocking heater bypass loop will bring temp down somewhat, but won't fix your problem since 185F is normal. 

A car running too rich will sputter and stall at idle or low rpm, but run OK on the road at medium rpm. Plugs will get black.

Vapor lock or water temp can't make plugs black. According to ZTherapy video (hidden in the British SU section) fuel pressure can affect the mix (more = richer) so that could possibly cause rich condition, as posted by others. Otherwise, I guess something to do with carbs: they look new, so probably mix setting.

The caps are freeze plugs. They look new.

 

Digression: My mom hired a guy to fix her truck. It was driving really wonky. I crawled underneath and saw that he had loosened the bolts to the cross member under the transmission. I tightened it up and told my mom but she wouldn't believe me, and she paid him soon after for even more useless repairs.

[jalexquijano]

Anyway i am taking the car to the radiator shop tomorrow for a complete flush and repair if needed. If this does not solve the problem, i will lean both carbs a Little bit to see if the rough idle and stalling issue is solved. If not then i will need to do a complete cleaning of the wáter passages. What kind of products are needed to do a flush and cleaning of the wáter passages?

[Zed Head]

23 hours ago, Zed Head said:

 I would check for that thermostat first, and block the line at the back of the cylinder head.  That should give proper flow and control, for cooling and carbs.

What about proper coolant line connections and the thermostat?  Too easy?

[jalexquijano]

Thermostat was removed yesterday!! Car is running with no Thermostat! Just ordered a 170 degrees farentheit thermostat OEM Nissan.

[Zed Head]

I meant the the thermostat in the picture I posted, at the carburetor heating line.  

Edited January 8, 2016 by Zed Head