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?