# Easy Way to Lower Running Temp on NAPS-Z



## RobertBlevins (Nov 6, 2013)

I have an '88 HB with power steering, AC, 5 speed, running the too-cool, we-don't-use-timing-belts-on-THIS-engine, NAPS-Z. It has 148k original, runs great. 

A few months back, I put a new water pump on it, did a bunch of maintanance on the motor, and replaced the intake manifold gasket. When I replaced the gasket, I decided to use larger water hoses under the intake than the smaller stock ones already in place. 

I double-clamped these hoses tightly on both ends. The ends were much larger than the stock inlets, so double-clamping seemed like the thing to do.

Next thing I notice after driving it is that the engine temperature will barely come off the cold side, although it does. It's just WAY lower than normal. Heater works, but takes twenty-thirty miles to really get going. I did some anti-freeze checks, etc. No problem.

Then it occurred to me the reason for the additional cooling was because of the oversize hoses. Truck runs great...only much cooler now because the water flow must be breaking records. 

Later, I will post up pictures, but you can probably figure it out from this post. My recommendation to NAPS-Z owners is DO IT. You won't be sorry. Just double-clamp those hoses down good. Anyone living in desert areas will be amazed, I think.


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## angelcigw005 (Nov 4, 2013)

This is interesting... let me try that...


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## TheRepairMan (Jun 30, 2009)

First off... welcome to the HB Truck forum, Robert!

And, I'm just a "little" skeptical about the larger hoses letting the engine run cooler. Generally speaking... if the cooling thermostat is in place and working normally, IT will keep the engine temps at a specific constant regardless of how much coolant you allow through. So... what I'm going out on a small limb to say is that most likely your thermostat is either worn out and opening way too soon, or mechanically broken in such a way that it is always partially or mostly open. I've replaced a LOT of broken thermostats in my day.

Now, I'm not dismissing that the larger hoses could, or may help... indeed, as long as they don't leak it certainly couldn't hurt, but hopefully we can get a few other members here to test out the theory and report their findings here. I'll keep tabs on this thread and see where it goes.

Oh, and BTW, if you couldn't tell, I'm sort of the "cooling system specialist" of the gang. Not that I'm necessarily more knowledgeable than others here on the topic, but almost always more interested as my background is in engine building and making them run cooler and more efficient. It's kinda always been my "thing" for about 40 some years now. You guys let me know if I can help!

-Roger


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## rogoman (Dec 16, 2004)

I have to agree with TheRepairMan. It points to a bad thermostat or it may be missing. If you're going to replace the thermostat, always go with an OEM unit, not an aftermarket one. Some aftermarket one's have been known to cause overheating problems.


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## smj999smj (Jan 1, 2006)

I lot of the aftermarket t-stats I've used on Nissans have made the engine run colder than the genuine Nissan part. On a computer controlled vehicle, running the engine too cold is not good, as it can cause the engine to run richer and/or not enter "closed loop."


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## TheRepairMan (Jun 30, 2009)

smj999smj said:


> A lot of the aftermarket t-stats I've used on Nissans have made the engine run colder than the genuine Nissan part. On a computer controlled vehicle, running the engine too cold is not good, as it can cause the engine to run richer and/or not enter "closed loop."


While all that is true, the car manufacturers have us running a little hotter than necessary, IMO, mostly to meet emissions limits sooner, but we all know that heat cycles, especially extreme heat kills any mechanical parts, electrical components, and all fluids over time. If you can reduce max temps by just 10% you may be able to double the life of some systems. 

Our vehicles waste more fuel producing heat than they do power, so anything you can do to help balance that out can make the vehicle run more efficiently, and last longer. One common way is to switch over to all fully synthetic lubricants. I see even further positive results by modding the cooling systems in several ways... but not running so cool that they won't enter closed loop. The lowest I've seen was down to 177*F and still operate normally. So, a 180* to 195* thermostat opening would be my personal choice. Synthetic engine oil does very well at those temps when run long periods also. Short runs at those temps or below can lead to moisture buildup from condensation inside the engine, so cooler isn't ALWAYS better under every driving condition or usage.

The only real way to know what your engine temps are doing to your oil is to have a lab run an analysis on a sample of your old oil. The lab will then compare and print out your test results to see if they are within the specified limits for contaminants and performance. 

This may help... http://www.bobistheoilguy.com/

-R


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