Hi,

I am almost done with the timing belt change on my Z31. I decided to change the thermostat since I am in there anyway. I also want to change the hose that goes up to the thermostat housing, but I don't know the name of the part.

I attached an image of the little guy I am talking about.

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Justin
1986 Z31 NA 2+0

It is the "engine to pipe hose" sometimes found under the listing for lower radiator hose.
Gates pn: 24026
AC Delco pn: 31008

Both are cut to fit. I wouldn't sweat changing that hose if it is good shape, I have never seen one fail. I would, however, strongly recommend changing 3 more things while you are there:
CHTS (coolant head temp sensor) just under the driver side cam gear
CHTS subharness
By-pass hose (90 degree hose attached to the thermostat housing)

I have seen several of the bypass hoses fail and they are nearly impossible to do without having it all apart like it is now. The CHTS and subharness are one of the biggest problem areas in the Z31 sensor world and are only really accessible during a timing belt job. All cheap enough to justify the added expense. Do OEM for the CHTS & subharness, aftermarkets have been known to read slightly off.

good luck Justin!

It is the "engine to pipe hose" sometimes found under the listing for lower radiator hose.
Gates pn: 24026
AC Delco pn: 31008

Both are cut to fit. I wouldn't sweat changing that hose if it is good shape, I have never seen one fail. I would, however, strongly recommend changing 3 more things while you are there:
CHTS (coolant head temp sensor) just under the driver side cam gear
CHTS subharness
By-pass hose (90 degree hose attached to the thermostat housing)

I have seen several of the bypass hoses fail and they are nearly impossible to do without having it all apart like it is now. The CHTS and subharness are one of the biggest problem areas in the Z31 sensor world and are only really accessible during a timing belt job. All cheap enough to justify the added expense. Do OEM for the CHTS & subharness, aftermarkets have been known to read slightly off.

good luck Justin!

Hi Greg,

Thanks for the tips! Where can I buy the OEM CHTS/CHTS Subharness replacements?

As far as the bypass hose, that is the one that is connected to the back end of the thermostat housing, right?

Thanks for the part # on the engine to pipe hose! I had read somewhere (maybe Az-Zbum's site) that those tend to leak so I figured I should change it.

One last question: Do you know which thermostat I should buy? I have seen 170F and 180F available. Depending on the company, I saw that some list the 170F as OEM and 180F as the alternate and the reverse too. I posted this on z31p but since you and I live in the same climate, I'd like your opinion.

Thanks again for the help! I wish I could order the parts and have them show up instantly so I can get the car running right away... but I am sure this will all save me headaches in the future

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Justin
1986 Z31 NA 2+0

I believe the 180 is the OEM temp and that works just fine on any Z. The only reason to go to the 170 would be for a highly modified Z which may get run on the track.

Yes, bypass hose is on the back of the thermostat housing.

I might have a new CHTS and subharness laying around, will check when I get home tomorrow. If not use Nissanparts.cc or CourtesyNissan, fast shipping and excellent prices.

I believe Courtesy Nissan will give you a discount if you belong to a Z club. It doesn't hurt to ask!

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Phil
1981 280zxt - Now in the care my son!
2014 370Z Sports Touring Roadster

I found the CHTS and the subharness (along with that engine to pipe hose... what a silly name!) on nissanparts.cc

Were you intending to use yours Greg? I can order a set from nissanparts (while they're still available!) if you need yours for any reason.

I was thinking of picking up the thermostat (Duralast brand) + bypass hose from the local autozone since they are a little cheaper. Strange thing is in the 1986 FSM for the Z31, it lists 170F as the OEM temperature...... there seems to be a lot of discrepancy about which is the factory temp. People on Z31P seem to be disagreeing too. I was leaning toward getting the 170F one myself... I don't intend on modding the motor a whole bunch, but I will eventually put the car on an autocross track. Is there any disadvantage to having a lower temp one?

Anyway... fun fun stuff! I am learning a lot from wrenching around. Hopefully I can put it back together right

I think the timing belt has been replaced before. I noticed that in addition to the dots on the cam gears (for timing marker), there looks like a black sharpie/paint mark at the dot too. Unless that mark is standard from the factory, I would bet that whoever changed the belt last drew those in. It would be great to have peace of mind after I change it myself though!

EDIT: I ended up just ordering the stuff thru nissanparts.cc.

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Justin
1986 Z31 NA 2+0

One last question: Do you know which thermostat I should buy? I have seen 170F and 180F available. Depending on the company, I saw that some list the 170F as OEM and 180F as the alternate and the reverse too. I posted this on z31p but since you and I live in the same climate, I'd like your opinion.

Justin,

The 170F is the safe bet. Actual running temp of the engine coolant should settle out at about 190 degrees which plenty. 200 degrees makes the heater work better in really cold climates, but on a 100 degree summer day the engine can reach meltdown temps in the heads.

Unlike the L-series engines where the thermostat is located in the outlet (highest point of heated coolant) the Z31 thermostat is located in the lower cooler "return" side flowing from the radiator back to the engine.

This coolant has been cooled by the radiator and therefore does not represent the actual running temp of the engine coolant as a whole (temp at the top of the cylinder heads.)

A "rule of thumb" for selecting a thermostat for the Z31 is to add 20 degrees to the thermostat temp rating to determnine the temp of the coolant leaving the engine via the top hose.

Or vice-versa, work the formula backwards and start with the desired coolant temp and subtract 20 degress to determine the thermostat temp rating.

The 20 degree factor is derived from the fact that most radiators only drop the coolant temp from the hot to the "cooler" side of the radiator by 20 degrees.

Each pass through the engine re-warms the coolant about the same amount.

The thermostat merely sets the upper level of the coolant temp. This assumes that the radiator has sufficient capacity to reduce the coolant temp in an amount which exceeds the amount of rewarming which occurs in the engine.

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Kim Blough

Hi Kim,

Thanks for the very thorough and technical explanation. After thinking about it for a while, I decided to install the 170F one and your post gives me some peace of mind!

The OEM temp. is a funny thing on these cars because the factory service manual shows that 170F is the rating but there is a huge discrepancy on which is the OEM temp. in the parts labels.

The original thermostat that I took out didn't have a stamp on it indicating which temp. it is rated at. I suppose I could test the opening temperature myself but I don't think I'm that curious.

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Justin
1986 Z31 NA 2+0

Been waiting over a week for my order from Nissanparts.cc ......

it hasn't even shipped yet. Order is still "pending"

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Justin
1986 Z31 NA 2+0

We get partz discounts from EXECUTIVE NISSAN in North Haven and Rock Auto online.

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1970 240Z

Time to give 'em a call

Called them twice already. On Monday they said the order will ship on Wednesday. I called again on Friday and they said the order will ship early next week...

I will go for executive nissan from now on! I wanted to order Rock Auto but I wanted the sensor from nissan (not aftermarket).

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Justin
1986 Z31 NA 2+0

In that case, best of luck to you man! Be sure to get in the Vendor Raves and Gripes to watch out for the rest of us!

In that case, best of luck to you man! Be sure to get in the Vendor Raves and Gripes to watch out for the rest of us!