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Overheating, trying to troubleshoot


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After a week or so of trying stuff, I thought I'd try to get some advice.

 

My 510 is overheating. While idling the temp gauge will slowly but certainly creep up toward the top of its scale and stay there, just under the red zone. With the engine under light load, it'll go over the H, deep into the red.

 

  • I've compression tested the system at 17psi, and it doesn't lose pressure.
  • Hoses look good, the top hose is very easy to compress with my hand when the engine's cold, a little harder to squeeze in (but still squeezes in quite a bit) when the engine's getting warm, and it feels compeletely firm just after overheating.
  • Ran it with radiator cap open until it got hot (and a little after that) and looking into the radiator with an inspection light, could not see the coolant flow. After turning off the engine when it started to overheat, coolant started bulging out of the radiator.
  • Replaced the thermostat with a new one yesterday, still no visible flow, still overheating.
  • Running the heater, even while the car is overheating, does not result in hot or even warm air.
  • After running hot, I get smoke from under the hood and a burnt smell, not steam.

 

This seems like a flow problem to me. Could this be a defective water pump or is it more likely that I just have an (or multiple) obstructions somewhere? Any tips on what to try next?

 

Is the smoke a sign I already f**cked up my headgasket? I don't see any thick white smoke on a cold start (and I also own an 200k mile RX-7 so I know what white smoke looks like), but I've heard/read that headgasket failures can be more subtle than that.

 

Thanks!

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Car is overheating.  No visible flow through the radiator.  Burps and overflows when hot engine is shut down.

 

Have you considered that it is time to have your radiator checked for blockage?  HINT!

+1

Yank the radiator out, yank out the thermostat housing and water pump and take a closer look inside to see if theres any gunk build up and pump water through at the top where the thermostat connects.Examine the pump and see if it needs to be replaced and get the radiator checked out.

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Drain the rad and look inside the opening. You should see the open tops of the vertical tubes. Is there a crusty deposit on them? This is from adding hard tap water. Coolant is constantly boiled away and more added concentrating the dissolved minerals until they deposit all over the cooling system. Deposits drop off and clog the tubes.

 

If your rad is in good shape lay face down with cap on and hoses up, and fill with a mixture of CLR and water. Let sit over night to dissolve the scale.

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is the vent hole, under the waterpump, leaking or making a weird noise..if not could be good.  Could your heater core be clogged?  What about your timing, is it retard?  What about your carb fuel mixture, is it too lean (check spark plugs), What about your belt, is too lose?  You could also have a bad thermostat (even new), could be installed backwards,  take it out and boil it in water and see if it opens at 185 degrees, have you done a compression check.  Also check your oil dipstick or oil cap and see if oil looks like choc. shake, if so then bad headgasket, also do a compression check, also check your plugs-if too clean (specially next to each other), then it steamed the crap out of them.  Good luck and keep us appraised of issue.

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water pumps mostly go bad cause the bearing otherwise they will alwasy push water unless the vain fell off.

Most times the thermostat is closed or barely open.

 

I would ck /flush the rad.

open the heaer cock on the driver side floor underneath and make sure the valve is open . the wires may bot pull them open as they age and get stuck.

 

as Racer X said ck the timming.

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you could do a compression check to see if headgasket is bad..if compression is low in adjacent cylinders or spark plugs are super clean, good indication of bad HG. Simple way to check is look at dipstick or oil cap, see color. If it looks choc. shake then bad HG. If compression okay, check heater core cuz you said not getting hot in car. You said pressure okay on Radiator, so maybe good.  Something is blocking the flow.

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Thanks for the advice everyone. I haven't had a chance to drain the radiator yet, but did figure out that the heater core is fine. The heat control was just no longer properly attached to it, but opening the heater flow by hand from the passenger footwell resulted in hot air.

 

After running like this for a couple minutes, I can feel that both heater hoses get hot, that the upper radiator hose remains completely cold, and the lower radiator hose is cold for the most part, only hot very close to the engine.

 

Pretty sure it's a clog in the rad now, and maybe a broken water pump as well. I know what to do next and will post here when I make some progress.

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Standard fan or thermo (electric fan)?

 

If its electric, what direction is it running?

 

Some people prefer to draw cold air from the front of the car through the radiator as opposed to the fan blowing (warmer) air from the engine bay through the radiator. Personally I have the fan drawing air from the front.

 

Wrong Pulley size on water pump and/or alternator may cause the pump to spin too quick, therefore causing water cavitation and slowing down water flow though the cooling system though this is rarely the case.

 

Apart from that, what everyone else has said (possibly clogged radiator).

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If the heater hoses got hot there is pump flow.

Drain the rad and look inside the opening. You should see the open tops of the vertical tubes. Is there a crusty deposit on them? This is from adding hard tap water. Coolant is constantly boiled away and more added concentrating the dissolved minerals until they deposit all over the cooling system. Deposits drop off and clog the tubes.
 
If your rad is in good shape lay face down with cap on and hoses up, and fill with a mixture of CLR and water. Let sit over night to dissolve the scale.

Is the thermostat positioned with the coil towards the engine?

Is the by pass hose connected? Without it, the thermostat is surrounded by stale non moving cold water while the rest of the engine overheats. The hose allows heater water to circulate past the thermostat to warm it. The hose exits the thermostat housing and is piped down across the front of the motor to the lower rad return hose. Check that some previous owner hasn't put a bolt in the end of the hoses and clamped it off.

 

bypasshoseLarge.jpg
 

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Fixed!

 

Thanks datzenmike and others for all the help.

 

Removed the rad, flushed it with distilled water, kept CLR in it overnight, and flushed it again. Carefully filled up the system again and burped it. Everything's normal now, the temp gauge stays within the first half of the M now after it gets warm.

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  • 3 weeks later...

A few days after my last update a new small coolant leak had developed at the front-right of the engine, where the heater hose and bypass hose connect. Proper flow and pressure in the system probably pushed the next deteriorating component over the edge.

 

The heater hose was obiously bad (with a bulge just after the connection) and the bypass hose didn't look too great either, so I replaced both generic aftermarket heater hoses and the little bypass hose with some OEM ones from eBay. While I had the hoses loose, I also flushed the heater core both ways with some distilled water and was rewarded with more sludgy, rusty water.

 

After I put everything back together with the new hoses, and new clamps for the bypass hose – destroyed the old wire-style clamps while taking them off, again filled the system up and everything seems to work great.

 

I also put in a 1L Evian bottle as a makeshift overflow reservoir, and it has collected a tiny amount of coolant since. I'd love to replace it with a more permanent overflow reservoir. Anyone know of a good one to fit to the right of (seen from driver's seat) the stock L16 radiator?

 

The only weird thing now is when heating up after a cold start, the temp gauge will first go up to a little over halfway between the middle to the top of the range, and then gradually go back to middle. This was also happening before I replaced those hoses. It seems like the thermostat isn't getting quite enough hot water from the engine to open up early. This consistently happens every cold start. But, it also consistently goes back to normal operating temperature and never overheats. Is this something I should worry about?

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Thermostats are cheap but get a good $10 one and replace it. I had one that would go right to the top of the run range then drop like a stone to below, then up again and drop, each time dropping to a warmer position until it evened out just below mid way up the run range. Always freaked me out so I got rid of it. I don't know what the long range effect would be if left. Maybe nothing.

 

Be sure your by pass hose from the thermostat housing isn't kinked ... it's easy to do on tight bends.

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  • 1 year later...

Closing the loop on this thread, since it is so google-able and might help others:

 

I recently changed my carburetor and intake setup (there's another thread on here), requiring me to do some work to the cooling system. Made the following discoveries:

 

1. The bypass pipe (metal line that runs in front of the engine cover) was completely clogged up in the narrow branch-off that goes to the thermostat housing. Similarly the fitting that was screwed into the housing was also completely clogged up. I used a small drill bit to clean both out and installed a fresh piece of hose between them.

 

After this and reinstalling everything else, the engine had a tendency to overheat. It was still a bit touch and go before the change in setup, but the problem was worse after. I ended up blowing a head gasket.

 

So, I replaced the head gasket and put everything back together again. Still touch and go.

 

2. Then, I finally replaced the thermostat, and the car now quickly warms up to operating temperature and stays there, not over, not under.

 

Lessons I learned:

 

1. Buy a quality thermostat (spend $7 at rockauto instead of $5 at autozone) and save a huge amount of money and time later on. When in doubt, replace. Get a few thermostat gaskets so you mess with it a few times and don't have excuses to procrastinate.

 

2. Check thin metal passages, especially in the thermostat bypass system. The thin metal tubes accrue crud really easily and it's made worse because the bypass line doesn't get a lot of flow (the path of least resistance is to just skip the thermostat housing altogether).

 

3. Listen to datzenmike. :)

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The temp on my 521 stays just a hair above the center line on the temp gauge.  Forget autozone, or rockauto for a thermostat, go to your neighbourhood Nissan dealer.

 

This is how I flush a L-16 engine that has been neglected.  Remove the radiator, and take out the thermostat.  Put the thermostat cover  back on, and if you want put the upper radiator hose on to direct water away from the engine and car.  Put the lower radiator hose on, and then take a garden hose, and put it in the lower radiator hose.

Remove the drain plug, near the back of the block, above the starter.   Get an air hose, with a blow gun on the air hose.

turn on the water, and hold your finger over the drain hole by the starter.  Let the block fill with water.  When the block is full, blow compressed air in the block drain.  You will be amazed at the crud that comes out of the block.   Let the block fill again, and blow air in the drain hole again.  Keep repeating this until the water being pushed out is no longer dirty.

 

With the radiator, you can use a similar method, filling the bottom of the radiator, and blowing air in the radiator drain.  You can also fill the radiator part way, and shake it so water sloshes around in the upper and lower tanks.

 

I then put everything back together, and use a Nissan thermostat, and new antifreeze.  You can buy 50/50 antifreeze, or but full strength antifreeze, and mix it with distilled water.

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Closing the loop on this thread, since it is so google-able and might help others:

 

I recently changed my carburetor and intake setup (there's another thread on here), requiring me to do some work to the cooling system. Made the following discoveries:

 

1. The bypass pipe (metal line that runs in front of the engine cover) was completely clogged up in the narrow branch-off that goes to the thermostat housing. Similarly the fitting that was screwed into the housing was also completely clogged up. I used a small drill bit to clean both out and installed a fresh piece of hose between them.

 

After this and reinstalling everything else, the engine had a tendency to overheat. It was still a bit touch and go before the change in setup, but the problem was worse after. I ended up blowing a head gasket.

 

So, I replaced the head gasket and put everything back together again. Still touch and go.

 

2. Then, I finally replaced the thermostat, and the car now quickly warms up to operating temperature and stays there, not over, not under.

 

Lessons I learned:

 

1. Buy a quality thermostat (spend $7 at rockauto instead of $5 at autozone) and save a huge amount of money and time later on. When in doubt, replace. Get a few thermostat gaskets so you mess with it a few times and don't have excuses to procrastinate.

 

2. Check thin metal passages, especially in the thermostat bypass system. The thin metal tubes accrue crud really easily and it's made worse because the bypass line doesn't get a lot of flow (the path of least resistance is to just skip the thermostat housing altogether).

 

:)

 

The first time there is the slightest hint of over heating... change the thermostat. It's cheap qnd easy.

 

Yes absolutely get an 'expensive' $7-$12 thermostat. That $8 you saved will cost you 10X at least later not counting the tow bill, and taxi home plus being stranded in the ghetto. If you opt for the $4 thermostat carry a revolver in the glove box.  

 

I had a similar seesaw temp spike followed by a big drop, back and forth until stable when I bought my 620. This is a good sign the by pass isn't working properly. It resolved itself... probably because as a new owner I ran the proper anti-freeze in it. Previous owners... you never know. 

 

 

very important!!!!!! dont use tape water if you dont have to.

 

If in doubt get distilled from WallMart, only a few bucks, or rainwater. Most other water contains dissolved minerals. That's what that crusty crud is when you look at the inside of your rad. 

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