2007 Xterra cooling system puzzler
 

My beach buggy is a 2007 Xterra SE 4.0 v6.

This past summer june I think it failed inspection for low temperature. According to DMV the operating temperature was to low. I did notice temp gauge was slightly below normal operating temp.

I figured the obvious culprit was the thermostat so I replaced it. While I had everything apart I also replace the fan clutch, belt and belt tensioner. Added coolant and took it for a short ride. Came back and relaised no pressure in the hoses, removed the cap and added more coolant. I figured it had air in the system and it was working it's way out. I did this several times. I began to get suspicious as I have now added several gallons of coolant and water.

At one point it throws a code (I can't recall the code) likely culprit the radiator cap. So thinking OK bad cap coolant is either bubbling out or ssteam being released. I put on a new cap. Took it for a ride to reset the codes. I understand the system needs to go through several cycles so a drive of thirty plus miles is in order.

I drive about fifteen-ish miles and notice the temp gauge is risining above normal operating temperature. The gauge stopped rising for a while slightly on the hot side. I was think perahpse there was still an air bubble. I pull over, no pressure in the hoses. Top hose is hot, bottom hose ice cold. Remove the cap low on coolant. I also notice around the over flow tank is green with coolant. OK, radiator is bad. The cap is not sealing there must be a bad flange?

I install a new radiator. Fill it up take it ofr a ride. Same thing no pressure low coolant Top hose is hot bottom hose is cold.

This morning I go to Advance rent a pressure tester. Two pumps of the handle barely 5lbs pf pressure cool comes spurting out of the cap and the overflow tank.

No fluid smell in exhast and engine runs fine, no stumbling or hesitation.

A bad water pump cold indicate the cold lower hose but wouldn't I have pressure on the top hose and why would fluid spurt out of the cape flange with so little pressure?

I can only assume a bad cap. I understand that you had an issue and then installed a new cap. I'd try another. Do you have the original (probably not)?

Your description of the issue is certainly baffling as it sounds like multiple different issues. I've run into situations like that, and they are frustrating. I'd not go on any super long test drives with a coolant issue. I'd try to stick close to home.

I think Nissan takes a special adapter for the radiator to pressure test It is small and weird, and specific to Nissan of that era.
I have done a few sets of Head Gaskets on these. I would do a block test next ( looking for combustion gasses in the coolant )
For some reason, I also remember a coolant bleed screw in a weird spot on the top of the engine.

I actually do have the original cap and another. I will try a new cap. No intention of any long rides until I figure this out.

Yes there is something weird about the caps. The kit had two Nissan style. One seemed to fit fine? I assume it was OK?

What do I need to do a block test?

Have you checked the two lines that go into the heater core? The originals were plastic and develop cracks. The new versions are metal and really inexpensive/easy to replace. Part of that job is burping the system which might need to be done here as well.

https://youtu.be/REjYjiO8xIs

I may have been mistaken about the bleeder . That may have been on older model Pathfinders . Ill look it up later for you .

longshot- T-stat installed backwards?
weird stuff. good luck.

oh yeah, how is the heat?

No I haven't checked the heater core lines yet. I know they have an effect on the system but when the fluid is full and the vehicle is warm heat works fine.

Yes, I know these vehhicles have a burp issue that is why I kept thinking I had an air bubble some place. I did jack up the front and let it run a while thinking that would clear it. At one point I even took it to a small hill and let it run about twnety minutes. No sisgns of anything dripping, coming out the tail pipe or anything during that time. This was after the new radiator. The only sign (and I wasn't positive at this time) was some wetness on the plastic cover directly behind the cap. But I wasn't sure if that was left over from some spillage during a fill up.

Thank you.

T-stat only goes in one way. For the most part I think the heat is work ok. When the fluid is low it isn't as hot. When topped off and warm heat works fine. I can see a coralation between the temp gauge and the heat. When temp goes up heat is hotter, when the temp falls heat gets colder. Obviously as the fluid is leaving the system and the engine gets hotter the heat goes up. When to much fluid is lost and isn't circulating the heat temp drops while the gauge continues to rise.

Wouldn't the pressure tester rule out the cap since it too is leaking? Even though it is new could it be a bad radiator?

Early Xterras can leak between the radiator and transmission cooling lines. It's common and bad news.

I had a 2013 with a bad overflow tank, but if I were you I would check my transmission fluid. Google the issue too, very common.

I am aware of that issue. It's not the transmission cooler.

What was your issue with the overflow tank?

Radiator caps blow coolant back into the overflow tank when pressure compresses that spring thingie which seals off the radiator neck. Coolant can now bypass that disc pushed down by the spring and will vent to the tank or to the ground through the neck pipe.

That said, I don't think your pressure tester is mating to your radiator properly.

With respect to air pockets. Nose up. 3500 RPM for 30 seconds. Shut down. Wait 60 seconds. Top off radiator. Repeat.

You have a leak. You know this. Is there any evidence?

Assuming you are correct and the pressure sensor isn't mating correctly, wouldn't that just prevent a seal and pressure build up?

It is my understaning the cap on this vehicle releases pressure above 16lbs. So why would the pressure tester be pushing coolant out at around 5lbs?

Yes, I think there is a leak some place. I haven't throughly researched the head gasket yet but have somewhat ruled it out. No build up on the old or new cap, no residue on the old radiator, oil looks OK.

I was sure when I pressure tetsed this moring I was going to find a leak at the lower hose (the one that stays cold). heat works so water pump should be working and is flowing coolant through the engine, upper hose is hot. I think this also rules out an interal blockage?

My thought was when the coolant got hot enough and expanded a fracture or crack in the lower hose was where coolant would leak out under pressure causing the cold hose and the pressure from the tester would reveal the leak.

No evidence of fluid loss while just sitting at idel in the driveway. While driving yesterday the only indication of fluid loss was wetness around the overflow tank. I have determined the fluid at the overflow is not coming out of the tank but at the connection of the tank and hose. A missing clamp?

The other possible indication of fluid loss was wetness on the plastic engine cover near the radiator cap. This may have been wetness from steam release. I havent definatively determined this yet as it my have been residual fluid from filling up the radiator.

Maybe I don't understand how the pressure tester works. Is it like the radiator cap but has a hose/pump to drop pressure into the system

Yes, Caps are color coordinated. Pick the cap that fits, then attach the hose and pump. Go to pressure and see if it holds for a period of time.

I put the cap on, took two pumps, the gauge moved from zero to maybe 5lbs. and coolant was gushing out out of the cap and overflow hose. Not just coming out gushing out of the cap with so much pressure it was hitting the propped up hood.

This is a similar tester.

http://forums.pelicanparts.com/uploa...1637363278.jpg

If it is OK I am going to bump for more thoughts?

Does the overflow tank pressurize if everything is sealed?

Let me see try. I will get back to you on that.

Yes it does.

I did read there is an air vent on the 4.0L but I have yet found a location.

That hose leaking on the tank is what undermines pressure.

Side note Advance Auto has a 140 and 180F thermo.

Explain to me please how the hose leaking undermines pressure? If the radiator is under pressure isn't that hose out of the system?

"Advance Auto has a 140 and 180F thermo." What is this?

Does the upper big hose have pressure on it when warm? I thought it had none. The overflow tank is integral to the cooling system. Lose pressure there and the system loses pressure.

Two different temperature thermostats.

No pressure on the upper big hose but it is hot.

No pressure on lower hose it is cold.

I haven't been able to determine if either of those hoses leak because I can't build any pressure. One pump and fluid spurts out of the cap and the tank hose.

Does the radiator leak if the regular cap is on?

From the cap? It doesn't appear to. I saw some dampness on the plastic engine cover that may be steam but I haven't determined that yet.

The reservoir has a pressure cap I see from pics. Yes?

My reservoir does not have a pressure cap just a regular.

The reservoir has two feeds. One from radiator neck and one to engine so I don't think coolant rages through it all the time like on some cars.

http://forums.pelicanparts.com/uploa...1637445424.jpg

However, if that tank pressurizes during operation that may be where your leak is if you are saying you see wetness at the hose.

If it is part of the pressurized system it will remove pressure from everywhere in the system.

Thanks Bob

I will take a closer look at the tank and hoses in the morning. I didn't even relaize there was a lower hose.

So I took a closer look per your recomendation. It does appear the tank pressurizes as you suggested. Fortnately I had the original radiator cap and threw that on. The system seems to be pressurizing but something is still seems out of whack.

After putting on the pressure cap, filling up the radiator, taking it to the beach ramp and purping the system per your directions, I took it for a test ride. I was esentially taking the same route as described above so I had some milage and occurence points as measurments.

Prior to the drive I cleaned off any spilled coolantand dried the surfaces to the best of my ability. I then took brand new white shop rags and wrapped them around the radiator cap and the overflow tank. If anythng was coming out of them they would have green wets spots.

I drove about three miles stopped and checked, all good and heat is pouring out the vents. At about mile ten into the ride I turned the heat off and put the windows down a few seconds to cool off. Windows up heat back on high.

At mile eleven the temp of the heat began to cool off. I pulled over to check the rags. Perfectly dry. Opened the overflow to relive pressure a slight hiss. The radiator appeared full. Put the caps back on drove home.

The heat never came back up to full temp. Pulled in the driveway rags are dry, radiator is down about a quart. I guess that could have been a air?

Pulled the drivers plugs to look and smell, all good. I will do the passenger side tomorrow.

Where is the heater core?

Sounds like air I’m the system to me since you are losing heat.

Passenger side behind the glove box. Yes, first thought was air. The 2nd Gen Xterra is notoriously hard to burp air out of the system. That is why as Bob suggetsed elevating the front running the vehicle filling the radiator and repeat.

I did remove the heater hose at the fitting and fill until coolant came out.

I am not compleltley convinced I have all the air out of the system yet since putting the pressure cap on the overflow tank. I will burp the system again and take for a test drive.

Rrrrrr, this thing is driving me crazy.

Yesterday took for the longest test drive yet about twenty five miles. Got to my destination squeezed the hoses before turning off engine. No pressure. Slightly turned the radiator cap not his or steam. Radiator looked full.

Looked around the expansion tank some coolant but not much. Noticed some wet spots on the driver door so looked in the wheel well. The wheel well was fairly wet directly below the expansion tank.

Today took the expansion tank out checked for cracks and leaks, no apparent issues, checked the hoses all holding pressure.

Is the water pump dead? Or plastic fin broke off and is clogging water jacket?

I’ve read the whole thread…definitely a head scratcher.

Strange that it’s not overheating.

I don't know where to go next but the water pump? I would think not if I have heat?

I wanted to see if I had flow through the engine but not sure how to go about that?

Edit: and I would guess maybe the thermostat isn't opening due to the curren temperature here 44 degrees? Although it was in the sixties yetserday. If the thermostat isn't opening no flow through the block correct?

And this hose (the lower hose) plumbs into th heater core. Again, I took this whole thing apart this morning and all appears to be leak free including the tank.

http://forums.pelicanparts.com/uploa...1637961447.jpg

Find out what's leaking in the passenger side wheel well. I mean no duh, but that's the dealio. Gotta kill the leak. Maybe given time invested, buy the whole expansion tank assembly?

Heater core hoses with a pin hole can spray really far and confuse but there should be some hint of where it originates from.