running too hot....or is it?

[Lee R]

Aftermarket temp gauge says 220...sometimes 230 if running hard up some hills before going back to 220. Stock temp gauge on dash reads straight up between C and H. Haven't had time to pull the sensor and test it so anybody have any ranges for temp? It's a 74 620 with an L18 and A87 head.

[banzai510(hainz)]

I would swap another stat in there right now. Why cause both gauges read high. so its shows soemthing is wrong.

 

make sure the lower hose is not collasping.

ck the timming with a light.

[KC Phirus]

Hainz, What should the running temp be?

All my datsuns gauges sit in the middle and drop down a bit with some airflow.

[Zeusimo]

180?

[pope_face]

I don't know any specifics, so I would go with what Hainz is saying, but I suspect the temperature gauge should read about the same as the thermostat rating... The thermostat keeps the coolant in the engine until it reaches a certain temperature, then lets it into the radiator to be cooled. If your thermostat is rated for 180 degrees, then it'll circulate the coolant in the engine until it reaches that temperature. I'm not sure what the difference should be, but I suspect a temperature gauge would only read a few degrees higher than the the thermostat rating.

[datzenmike]

I like to run 1/3 of the way up into the run section of the gauge. Probably 185/190 ish. As Hainz said change the thermostat, they're cheap and easy to do. If it reads the same then check timing is 12 degrees and not retarded.

[Z-train]

The original post suggests the radiator is at its cooling limit.

[datzenmike]

Borrow an infra red gun or whatever they are read the temp at the thermostat and lay it to rest. I ran my L18 at the very top of the rum range for a week and you would never know anything was wrong. It didn't ping or run on when shut off and started hot no prob. I replaced the thermostat (which was brand new BTW) with another and now it's in the 1/3 up into the range. So the top of the range can't be that high.

[ggzilla]

+1

 

Dash gauges are not precision, so measure the temp some other way. The temp should be within 10 degrees of the thermostat, but it's OK to go up a bit with heavy loads. Many cars run at 220 degrees -- it won't hurt the engine -- but it shouldn't run that hot with a 180 thermostat.

[Lee R]

NOW I'M NERVOUS!!! So I just replaced the thermostat this morning with a 180 degree. The old thermostat was stuck open.....does this mean it should have been running cooler since the coolant was just flowing constantly instead of regulated by the thermostat? I have not started it yet...waiting for the gasket sealer to dry.

 

 

 

H E L P

[banzai510(hainz)]

As I stated before even it both gauges are wrong but there were consisitant as both indicate that its Hotter than so called normal.

 

Now You say the stat was open? Then I would think it would run cooler as it is winter time and would nto ready that hot.

My Cherokee was reading cool all the time. People said change the stat. I said it cant be it.I swapped 2 sensors. Still no fix. Pull out the stat and one side of the holder/stand or whatever yu want to callit was broke which cause the plaet eto be partial open. I was going to suggest to drill a 1/8 holen the stat as a small bypass so it graually warms up instead a spike if not equiped with a heater line/lower stat bypass.

But for you open stat and is still hot. This will pertain what to Z train has said. then look at radiator or weak headgasket

 

 

Like earlier ck the lower hose if its soft and rev up the motor and see if it collaspes.

 

 

You loosing water?

 

could cbe the head gasket is weak and blowing hot gas into the coolant.

[ggzilla]

Why don't you follow our advice? Measure the temperature some other way than by the dash gauge. Borrow or buy an infra red gun or whatever. Or buy an external gauge and connect it temporarily.

 

If you don't want to do that, give the cooling system a pressure test.

[datsunaholic]

Guys, "straight up" is the middle of the stock gauge in a 620. ALL my 620s, when the gauges work that is, read in the middle normally. When I had a badly corroded (mostly plugged) radiator it would climb all the way to the "H" mark, which was 230 on the mechanical gauge since I had both. It was particularly bad at idle or going up hills, not so much on level terrain or downhill. There was a 40-degree swing in temperatures. New radiator solved it, then the mechanical gauge failed.

 

But, if the mechanical gauge is reading 220 and the electrical is reading mid-gauge, one of them is wrong. The electric ones are notoriously unreliable, though, but usually just don't work at all due to corrosion of the wires or the housing. The mechanical gauge can read high if the tube gets heat-saturated. That happens when you have the metal coil-wound tube lying on the exhaust manifold.

[Lee R]

As I stated before even it both gauges are wrong but there were consisitant as both indicate that its Hotter than so called normal.

 

Now You say the stat was open? Then I would think it would run cooler as it is winter time and would nto ready that hot.

My Cherokee was reading cool all the time. People said change the stat. I said it cant be it.I swapped 2 sensors. Still no fix. Pull out the stat and one side of the holder/stand or whatever yu want to callit was broke which cause the plaet eto be partial open. I was going to suggest to drill a 1/8 holen the stat as a small bypass so it graually warms up instead a spike if not equiped with a heater line/lower stat bypass.

But for you open stat and is still hot. This will pertain what to Z train has said. then look at radiator or weak headgasket

 

 

Like earlier ck the lower hose if its soft and rev up the motor and see if it collaspes.

 

 

You loosing water?

 

could cbe the head gasket is weak and blowing hot gas into the coolant.

 

 

Not leaking water and the lower rad hose is not collapsing. Just hooked it back up, topped with coolant and let it idle for about 15 minutes. Took it for a drive for another 15 minutes or so and so far the temp is right at 200.

 

 

 

I have heard running with no thermostat can be worse because the water just rushes through the radiator without it getting a chance to cool hence the higher temps. Maybe this is what was going on with the stuck stat. I'll be heading to Harbor Freight for a thermal gun.

[Lee R]

Why don't you follow our advice? Measure the temperature some other way than by the dash gauge. Borrow or buy an infra red gun or whatever. Or buy an external gauge and connect it temporarily.

 

If you don't want to do that, give the cooling system a pressure test.

 

 

Is it that accurate for what the water is inside the hoses? What would be the variable between say the housing temp and actual temp inside?

[Laecaon]

Its fairly accurate. You touch it when its hot. It is aluminum so it will get hot easily. A IR gun will get a fairly reliable reading, way more reliable than unknown gauges. A factory gauge can read colder than it is from corrosion.

[datzenmike]

I have heard running with no thermostat can be worse because the water just rushes through the radiator without it getting a chance to cool hence the higher temps. Maybe this is what was going on with the stuck stat. I'll be heading to Harbor Freight for a thermal gun.

 

Rubbish! No engine is going to overheat because it does not have a thermostat. The whole idea of a thermostat is to restrict flow so the enging CAN warm up. Without one the gauge won't even get up the the bottom of the run range.

 

If you ever have to take that thermostat out again you will be sorry you used any sealer on the gaskets. Sealers basically glue the parts together and make them impossible to take off later. Nissan didn't use a sealer on there when they put it together and neither should you. Sealers are only used if the gasket surface is damaged.

 

Did you get an auto shop to shoot the temp of the thermostat housing yet?

[Lee R]

Rubbish! No engine is going to overheat because it does not have a thermostat. The whole idea of a thermostat is to restrict flow so the enging CAN warm up. Without one the gauge won't even get up the the bottom of the run range.

 

If you ever have to take that thermostat out again you will be sorry you used any sealer on the gaskets. Sealers basically glue the parts together and make them impossible to take off later. Nissan didn't use a sealer on there when they put it together and neither should you. Sealers are only used if the gasket surface is damaged.

 

Did you get an auto shop to shoot the temp of the thermostat housing yet?

 

 

 

Finally got the thermal temp gun. It's very addicting as I have been using it on a bottle of beer, inside of my shoes, running tap water....anyway!! Here are the readings after warming up and driving around for a few miles then some time just sitting and idling.

 

 

 

Thermostat outlet neck - 176.9

 

Radiator - 155

 

Upper Rad hose - 164

 

Lower Rad hose - 136

 

 

Now the previous owner had installed the water temp gauge on the lower rad hose. With the lower rad hose temp at 136, the aftermarket water temp gauge in the car was reading 198-200! Quite certain the temp sensor and or gauge is busted. I'm just going to swap it out for a new one and install it in the thermostat outlet neck.

 

Thanks all for the help!!! Any further pointers or criticism is still welcome. :) Going to set the timing this weekend.

[ggzilla]

Another success story! To find out the engine is not running too hot, is nice to hear.