Tech tip 2

 

The humble engine thermostat is often overlooked when performance issues arise and can have dramatic effect in particular the twin turbo and a lesser but just as important level on the non turbo zeds

 

The thermostat is very commonly misunderstood in how it functions and this can in turn lead to ignoring the running issues that it can directly cause.

 

The unit works from cold by restricting the flow of water around the engine block with the exception of a small by pass hole which prevents the water pump been overloaded. A simple but effective temperature sensitive action moves the valve either open or closed according to water temperature.

The restriction mentioned earlier in the water flow is designed to get the engine up to temperature quickly and efficiently and also assists the heater matrix warm up time.

 

Once the designed engine temperature approaches the stat begins to open, this allows extra water to now flow into the block and onwards. Now this is where the story ends for many remember the common misconception that I mentioned earlier? the stat is more than just an open and shut valve it is a modulating stat which in essence the stat will close again slightly after the initial opening due to the extra movement of water through it. As this now restricts the flow again the temperature rises slightly and the stat responds by opening again, this action or “modulation” is what “regulates” the engine temperature at a mean average of around 80 deg c

 

Now take a look at the two stats below, a used and faulty one to the left of the pic`s and a new Nissan item to the right of the pic`s.

 

Clearly the faulty one is open and as it is at room temperature it should be closed like the new one, and what effect would this have on a zed engine?

 

Surprisingly a LOT!

 

The twin turbo model had built in safe guards to prevent hard boosting when the engine is cold by acting on the boost solenoid valves, now this is different to safety boost as the ignition is not effected so does not feel so obvious the temperature needs to be above 68 deg c approx. to give full boost.

 

Now typically a stat jammed open will have the effect of reducing the engine running temp by 15 to 20 deg c which clearly will mean the engine never gets out of the cold running restriction, add to this the ecu will be fuelling accordingly to the lower temperature which is not good for mpg!

 

Sometimes a stat although jammed will be only slightly open this then means the engine will actually hover around 70deg c, so full boost is available, until you give it some beans and the extra cooling air and water volume increase reduces the temp by a small amount that is below the full boost temperature, this can end up been a cycle of good boost ...bad boost....good boost ...bad boost.....

The non turbo will of course be less effected, however an engine not running at full temperature is not running efficiently and will suffer accordingly too.

 

So what's to do? simple change the thermostat, an easy and quick job and full stat “modulation” and engine temperature “regulating” returns and so does the happy engine performance we all crave.

 

 

Jeff TT

 

 

 

Another quality read Jeff! Keep them coming :)

excellent thread matey, may be the cause of my running probs at the moment.

 

al.

So how can we tell if our stat is working how it should? will the engine take longer to warm up, will it hover around 65-70degrees-?

So how can we tell if our stat is working how it should? will the engine take longer to warm up, will it hover around 65-70degrees-?

 

If the thermostat cannot close properly it cannot regulate so the engine water temp will hover around 62degc at tickover and rise on the road under slight load to about 70 deg but will drop when air in through the rad gets higher.

 

It is easy to see on the ConZult but it will also show out via the heater been slow to warm up and go cooler when you go faster, the temp gauge will show around the 7 O`clock area rather than the 9 O`clock position

 

Other signs to look out for are raised tickover speed and poor fuel economy.

 

Jeff TT

any links on how to change and where to find so called thermostat

any links on how to change and where to find so called thermostat

 

Will get some pics together tomorrow and post it.

 

Jeff TT

nice one, i have very poor fuel and high tickover and it takes a good 15min drive from cold to get a bit of warm through the heaters

Excellent post (again) Hmmm my boost issue is slowely getting narrowed down... get good boost after hitting the 9 oclock mark for the first 5 mins then get not so good boost for the rest of the drive (until I switch it off and use again the next day) :bow:

i was thinking today how my new slicky water temp gauge sits a little below the other zeds, maybe about 8'o'clock compared to a little over 9.

 

Is there anthing else i can do to check this?

i was thinking today how my new slicky water temp gauge sits a little below the other zeds, maybe about 8'o'clock compared to a little over 9.

 

Is there anthing else i can do to check this?

 

 

ConZult check is the easiest way.

 

Jeff TT

If the thermostat cannot close properly it cannot regulate so the engine water temp will hover around 62degc at tickover and rise on the road under slight load to about 70 deg but will drop when air in through the rad gets higher.

 

It is easy to see on the ConZult but it will also show out via the heater been slow to warm up and go cooler when you go faster, the temp gauge will show around the 7 O`clock area rather than the 9 O`clock position

 

Other signs to look out for are raised tickover speed and poor fuel economy.

 

Jeff TT

 

 

My stock temp gauge is useless goes to about 7 oclock and doesnt move while my aftermarket will get to about 74-76 and change depending on speed and weather so im sure im ok. heating is hot, tickover settles to about 900rpm cant get it to go any lower maybe its down the larger injectors. ive tried setting the base idle etc it just goes back to 900 when i reconnect the idle valve connector. tps is set correctly also.

 

I have noticed that the cars runs rich on full throttle but sits nicely on tickover around 14.7afr on the wideband... some boring info for you there jeff :D

Nice one Jeff, a couple of questions.

 

The bypass hole that you mentioned. This is the little hole with a peice of copper wriggling about in it right ?. When fitting am I right in saying that this always needs to be at the top of the thermostat to prevent air locks or is this nonsense ?.

 

Also the good boost / bad boost you mentioned reminded me of a recent dyno chart !!.

Is it possible the thermostat could give this read out on the dyno ?

 

any links on how to change and where to find so called thermostat

 

Will get some pics together tomorrow and post it.

 

Jeff TT

 

 

anyone got any more info or pictures on where to find the thermostat?

The thermostat on my daily ride (Primera 2.0 TDS) jammed shut on my thirty mile commute to work a couple of weeks ago, I didn't notice the temp gauge rising until too late. :eek: It happened to be the coldest morning of the year -5 degrees!

By that time, my water had all boiled away out of the expansion bottle leaving me with an extremely hot engine. Two hours and one uplift recovery later (only cost me a bottle of whisky), thermostat is replaced and all is well again.

All for the sake of a six pound Nissan thermostat (ten pounds at the local motor factors by the way) which has worked perfectly for the last one hundred thousand miles - strange how it should just pack in like that though. :confused:

If you look at the engine from the front, you can see your two main metal water pipes, the thermostat is located behind the lower of the two, can be quite awkward to get to the bolts, maybe remove some bits and bobs, and small hands are a bonus ;-) The pipes are sealed with liquid gasket by the way... HTH

I think i have an open thermo :( all the way to amsterdam and back temp wouldnt rise over 65 or so during motorway driving sometimes as low as 59, BUT when idling it just about gets to 70 or so. Think il need to do some investigating, ive not heard the fan kick in for a long time now, probably since summer. Either my gauge is faulty or open thermostat :( Really cant be bothered to open her up though. Thinking this might be why i get some black smoke when blipping throttle on tickoover and when pulling away.RUNNING RICH dam it.... :( firstly i might boil some water and cover the gauge sensor see if it reads 99-100 degrees at least then il know if my gausge is reading correctly before i start taking it apart.