I have a thread posted in the 5th gen forum too regarding this issue. I thought posting it here made more sense since some would have already experienced similar issues.

I figured out that there indeed is a leak and eventually making it to the oil. I threw in some UV dye into the coolant and after a week it showed up under UV light in the oil cap.

I have 150K on the motor and have suspected the pump. But then I am not sure too where the problem could be, some say head gasket while others say it is the pump.

If the gasket is failing then there should be oil in the coolant too. I only see coolant in the oil leading me to believe this is a unique problem. I don't see any leaks of coolant under the car though....

Any suggestions...

Coolant is thinner than oil, so maybe the viscosity has something to do with oil not being in the coolant as expected with a bad head gasket? Not sure if my logic is right or not.

Does the engine make any above average noise? Sound like a waterpump at all ??? If it was the pump, I'd say you would be able to hear it. Easy way to check is to pull the cover on the TC cover (it's in front of the engine mount, small 4 -10mm bolts cover) and see if it has a leak there. I am guessing head gasket beasue the UV showed up on top of the engine. Also, taking into affect what pro90 said about the coolant being more viscous - I wonder if you did a compression check if it'd show anything? ???

There is no abnormal sounds coming from the engine bay.

The UV light picked up the dye where the intake meets the block. Right below that is the head gasket (6 inches below the metal head gasket ends protruting out) I see no coolant.

This really is baffling, I would expect a leak to show up where the head gasket is and not on the valve cover gasket. Could the coolant pass the head gasket and cylinders and make it to the intake resulting in the valve gasket logging the dye...).

Anyway, the diagnosis is a dealership item, I don't want to spend all this time chasing a ghost. The cooling system is a no-no, too many components to deal with.

if you're going to take it to the stealership, why post here then ???

you asked for our opinion, so we'll see if one of us is right .... take it in, get it diagnosed and see.

change the water pump

Took the vehicle to the dealership in Bay Area, CA and the service person out there looked at the vehicle and changed the radiator cap while I was there. He explained how the coolant made it to the valve cover, his explanation was under pressure the radiator cap sprayed that all over the place. OK, I get that part and was impressed that he convinced me -- he also told me to keep the reservior level lower than what it presently is..

Then coming to how traces of coolant made it to the oil cap. He told me there must have been some kind of flashover in the engine resulting in the UV trace. He told me he has owned 3 generation of maximas' and never heard of a head gasket issue -- so he plainly told me to stay clear from that angle. If the gasket had compromised there would be tell-tale signs of failure.

I am supposed to go back if the coolant falls lower with a new radiator cap. Overall charge was $15+tax for the radiator cap, 10min while waiting for service at the dealership, he told me to go home and rest in peace.

what do you keep the coolant level at? above the max line? I still think you could have a leaking o-ring on the water bump. thats pretty common. but like the dealership said, wait to see if its still happening now.

^^^ agreed

A faulty cap would cause the system to not pressurize, thus overheating the car. A leak on the other hand would cause anti-freeze / coolant to go where it is not supposed to, i.e. the oil fill cap. I think you'll have more problems and the excuse will be ... well, now that we fixed the pressure on the system with a new cap, it must have blown the O rings in the water pump. ... Can I get a witness up in here!?! LOL

Something I learned a long time ago was that people will give you the "quick fix" only to bring you back for the real problem. What I mean is ... he "fixed" it for now, so you are starting to trust what he tells you, so when he explains as I just did how fixing one problem caused the other (which is bs btw), you don't question it, you trust them and go for it.

I will take the water pump cover off and check for UV signature around the pump. Its is 2 hr job and I will have to do it over the weekend.. Thx for ur inputs.

If you're gonna be pulling the pump, do the TC tensioner at the same time, you need to remove it anyway. That is ... if you are replacing the pump.

Definetly, thanks for giving me a headsup on the TC tensioner. I checked the prices online and they are $70 each for the water pump and tensioner.

BTW, on my previous reply to noises coming from the pump area, there is some low pitched growl at normal speeds and a fairly audible sound when steep incline under hard acceleration.

Finally, generally for the 4th gen folks who replaced them, what has been the avg life of the water pump?

I did my pump at around 109k and just did the TC tensioner at the same time. You might check AutoZone for better prices. I got my stuff local and don't remember paying that much ... seems steep. The low growl could be from the TC being loose (due to a worn out tensioner) give it a little slack. It could also be the water pump bearings going out.

Do you smell anti-freeze ever .... and have you seen it drain with the oil when you change the oil? You might not be able to tell if there is anti-freeze in your oil ... sometimes it's hard to tell. If the oil is more runny than normal, chances are it's laced with coolant.

A used oil analysis should tell you if there is antifreeze in the oil.

If there is, it's best to get the leak fixed ASAP because antifreeze in the oil will damage the bearings.

Update: I got the pump and tensioner done for $600. OEM Pump = $104 and Tensioner = $68. Labor was discounted as the guy was my wife's patient ($350 for labor + $50 for parts like new drive belts, coolant, oil change + tax).

He did a compression test and determined there was a small dip in pressure with no obvious leaks, therefore he went ahead and replaced the pump and tensioner. He redid the compression teat with the parts installed and there was no loss of pressure. He put in Peak Global for the lost coolant once the pump came off, I am not happy with that shortcut. Anyway, I will do a complete flush soon to get the whole system back to Nissan Long Life Coolant.

I am hoping this is it....I am going to do and UOA to put my mind to rest.

please don't type in yellow. It looks at thought there is nothing typed in your orginal post for those of us who use the white background.
try again.
"What's up guys?New here with a similar problem.

Car runs great, has a bad bearing sound(like and idler pulley bearing) while running and is filling the crank case with coolant.Idles smooth.No CEL.

Are these waterpumps known for dumping coolant into the engine during catastrophic failure?

I plan on pulling it apart tomorrow but your opinion would be appreciated"