engine doesn't get hot

[Frankensteinz2]

Hey guys,

I can't seem to get my engine over a quarter of the way on the temp gauge, i used both a 180 and a 160 thermo from msa and with the same results, i had a mechanic put one of those guns on my thermostat and it read only 140 after a long drive

I know i shouldn't be complaining givin the z's overheating problems but because the engine doesn't get very hot it seems to not like to idle

any ideas????

[Curtis240Z]

Is your clutch fan frozen so the fan runs all the time?

[Frankensteinz2]

thats a good idea, however i have had a frozen fan clutch before and it makes a hell of a wind noise when its frozen, and i haven't had any of that, also the fan clutch is realitively new

[ozconnection]

What was the mechanics conclusion, and why was it there?

[Gary in NJ]

Bad sensor or bad gauge.

Put a meat thermometer on the rad to determine the actual temp.

[Powerglide]

Zs don't have an "overheating problem". And a motor that runs at 140 degrees will return poor fuel milage and will wear-out in no time...

[ozconnection]

Zs don't have an "overheating problem". And a motor that runs at 140 degrees will return poor fuel milage and will wear-out in no time...

Agreed, but what's causing this to happen to his engine? Strange!
In the meantime, you could try a hotter plug to get it to idle better.

[Inf]

I'd make sure your thermostats are at least working... I know the odds are low, but maybe you have two defective ones that are staying wide-open regardless of temperature.

Think of it this way: your engine is producing a ton of excess heat as it produces power, and that heat has go to somewhere. Your engine-block and cylinder head are a piss poor heat exchanger with the air, and really can't get rid of that energy without the radiator.

If your mechanic measured the thermo housing temp, and only got 140, that would tell me that the coolant was actually running through the radiator after all, most likely uninhibited.

You can test your thermostats by suspending them in some string in a pot of hot water with a candy thermometer (and I say suspending them in order to keep them off the bottom. The bottom of an actively heated pan will be hotter than the water inside, and if in contact with the thermostat, will conduct a lot of heat into it, affecting your test).

[EScanlon]

My first thought was that your thermostat was stuck open, or not installed. The Fan's clutch was mentioned, which if the thermostat was functioning properly wouldn't have that much effect.

Are you sure all six cylinders are firing? You may be "running" but you may not have all six working. It's a WAG, but....

The last suggestion I have is similar, have you had the carbs balanced properly? Just another WAG.

E

[Zs-ondabrain]

If you have an air pocket at the thermostat, in the housing, It will not heat up enough to open the thermostat. Park your Z on a hill, so that the front is higher than the rear, this should help force the air to the highest point so you can completely top off the cooling system.

180 is ideal but I've known people to run 185 and 190's
I have a Huge Aluminum Radiator, 50/50 coolant and a 180 stat and my guage still says it's an 1/8" below center on the gauge. Not a bad thing but I was concerned at first. took longer to get her up to temp for best operating temp.

Dave

[yetterben]

Take a reading between cyl 5 and 6 on the drivers side of head. Very and i mean very unlikely you are running that cold even with no thermo in there. If you took it out for a spirited run and banged threw 1-3rd wot even with no thermo the temp would be 160-200.

Back of head between 5-6 is gonna show 20 more than whats in radiator as well.

Chances are your thermo is stuck wide open but i am guessing faulty testing equipment.

[Frankensteinz2]

ok ill stop by the autozone and give it a nice go through with your suggestions, i know this is a idiot idea, but the spring side of the thermo goes on the bottom right???? hey don't laugh

Umm alright ill go through all these and see what i come up with, fyi it read 140 with the car off after a long ride, and i was there for an inspection, not the cold temp, he just told me it as a after though and hit it with the gun

ill post after some tests, thanks for the suggets

[mlc240z]

Nasty idea, don't even know if it's mechanically possible but.......

a crack or hole internally in the engine which is allowing coolant to bypass the thermostat?
Allowing constant flow of coolant even with a closed thermo?

[ozconnection]

How old is your water pump?

I've seen old ones where the vanes have eroded away from not using proper engine coolant and the water pump dies a slow death. Remember it's the coolant that carries the heat away from the head and block to the radiator and a faulty pump might be the problem.

[ozconnection]

Nasty idea, don't even know if it's mechanically possible but.......

a crack or hole internally in the engine which is allowing coolant to bypass the thermostat?
Allowing constant flow of coolant even with a closed thermo?

FYI, not all the coolant goes directly through the thermostat in some models of Datsuns. In later models, Nissan put in a bypass line from the thermostat housing to the inlet side of the front cover just before the water pump.

This setup was designed to lower the pressure of the coolant in the block so that excessive pressure wasn't forced through the engine before the thermostat cracked open. An example is pulling straight onto the freeway, accelerating up to speed, using revs to do so and with the engine cold and thermostat still closed.

[yetterben]

Oz makes a good point i pulled my pump during my rebuild and saw the steel veins where being eaten away. Since have switched to the ld28 cast pump.

[Frankensteinz2]

all better, it was 2 faulty thermostats, 1 from MSA, 1 from O'reily's, went to autozone today and bought a 192 degree thermo, put it in and let her idle for a bit, thermostat reads straight up and down, i got a gun and the bottom of the thermo housing reads 180 at running temp

thanks for everyones help, don't buy cheap ish

on to the next thing to fix on the old girl

Frankie

[EScanlon]

How old is your water pump?

I've seen old ones where the vanes have eroded away from not using proper engine coolant and the water pump dies a slow death. Remember it's the coolant that carries the heat away from the head and block to the radiator and a faulty pump might be the problem.

Oz makes a good point i pulled my pump during my rebuild and saw the steel veins where being eaten away. Since have switched to the ld28 cast pump.

Wouldn't the eroded vanes result in an engine OVER-heating and not UNDER heating which is what his original (now resolved) complaint was?

2¢
E

[geezer]

Wouldn't the eroded vanes result in an engine OVER-heating and not UNDER heating which is what his original (now resolved) complaint was?

2¢
E

Glad the problem is solved.
When I read Oz's post I took it to mean, it would cause the engine to run hotter with damaged vanes in the water pump but because the coolant wouldn't be circulating, the coolant could possibly be trapped, not moving and much cooler at the temp sensor, thus giving the lower temperature reading at the gauge, when in reality, the engine is running hot. I thought to myself... hmmn, that could be a possibility.