Overheating advice

[4x4forfun]

I have been having higher engine temps lately and I know I don't have a leak or anything like that going on. I did a pressure test on the cooling system and it is holding pressure just fine. The radiator is pretty clean inside and out. But when I get on the fwy and go about 70 mph with the AC on during these last few HOT weeks the temp gauge moves up to the top end of the safe zone. I replaced the thermostat about a year ago.
 Has anyone else experienced this?
 Has anyone installed an electric cooling fan unit and ditched the belt driven unit?
 Has anyone changed out their radiator with one that has an extra row or 2?
 If so I want to hear about it and if it helped.
 
 I did flush the cooling system when I changed the thermostat and also changed every water hose then as well. Even the heater hoses. I am not seeing water in my oil or vice versa. I also don't have the skidrow skidplates on, as I take them off when not needed and relaced with the stock plate. I have to wonder if the thermostat I got is bad and not opening up soon enough.

Thank you in advance for your help

[Bobby B.]

Is there air in the system?  Once you open up the system to flush it, you have to bleed it.  There are, I believe, two bleeder valves on the top of the engine.

If you want a better radiator, radiatorbarn.com has all-metal units with extra cores for the SC models that'll go right in. 

You definitely have some issue.  I've got an SC with full skids and lights/winch blocking the front and my temp gauge never goes over half-way; normally it's a crack below half at all times (wheeling in full desert heat, towing, etc.)

[4x4forfun]

My X is not an SC model but I might check out the extra row radiator anyway. I like the idea of an all metal unit over the stock plastic capped unit. I did the bleed the system from the one screw on top of the plenum when flushed it and when I filled it back up after the flush. You say there are 2 screws for bleeding. Where is the second one located or is it for the SC models only? My manual only shows the one on the plenum.

[Bobby B.]

Memory could be faulty, but I thought there were two. Could be wrong.

[4x4forfun]

Bobby,
 Once again you have come to my aid on perplexing X questions.
Thank you.

I'll recheck the manual when I get a chance and see if I missed one of the bleed points. I took a look at radiatorbarn and ran a check on both the SC model and non SC model but they didn't offer anything over a single row. I may call them and see if their catalog offers up anything different. I am going to remove the bleed plug tomorrow morning and see if there is any void with air in the plenum. If not, I am going to pull the thermostat and "boil" it to see what temp it opens up at this weekend.

Thanks again Bobby

[Bobby B.]

Definitely call them.  They used to offer a three row, then supposedly they only offered the one and two rows. 

Only other things I can think of would be, like you said, the t-stat, be it bad or facing the wrong direction, blockage from the AC condenser, overheating from the trans (if you have an auto, they run the fluid through the base of the rad) or even the fan clutch (if it doesn't disengage properly at speed).  Hopefully it's not something like a bad head gasket or cracked head.

[4x4forfun]

My plumber neighbor brought over his optic cable thing he uses for inspecting pipe interiors and we shoved it under the intake and didn't see any leaks or signs of leaking on the mini TV screen. So I did another pressure test and it held perfectly with no drop in pressure. I think that would rule out the head gasket or cracks in the head or any leaking overall.  There never seems to be any loss of radiator fluid or drop in its level.
  I plan to do another flush this weekend when I change the oil and filter. If that doesn't improve the situation then I am going to pull the tstat and replace it with a new OEM part and if that doesn't work I am going to change the radiator. Hey, It's only money and time, Right?

[fleury123]

There could also be a clog or lower flow in the radiator its self. I had a  similar issue. I did the gamete thermostat, hoses, and pressure checked all tested good after replacing the ones I could. I still had higher temps. I took my radiator and had it rodded and all kinds of stuff came out.
********

I am not a big fan of the plastic end caps of the stocker and recently had to replace due to a crack on the neck of the filler area.

[4x4forfun]

Fleury,
 Thanks for the advice and you too Bobby B. I replaced all the hoses last year and just replaced the fan clutch and tstat last week. I actually changed the tstat to one that opens at 170 degrees as opposed to the stock model 180 degrees. The old fan clutch felt really loose compared to the new one.
  I am going to replace the radiator next. Not too worried right now with the cooler weather but it is something I want to take care of, though, sooner rather than later.

[superslidestyle]

I bought the KOYO japanese brand OE replacement radiator from (1-800)Radiator in LaVerne, CA for $130 (OE is $115) and it has an all metal core and 89 rows vs. the OE type which has a plastic top and only 76 rows. Comes with a "Lifetime Warranty" too.  It worked great in the year that I've had it on.  Even with a new water pump, Nismo T-stat, Nismo cap, Koyo radiator, and some new hoses, I could not avoid the problem I encountered.  My overheating problem came from two broken head bolts which allowed coolant to enter the piston chamber and three (3) leaking hoses, one above the t-stat housing and two by the firewall under the plenum (hard to reach).

I'm doing my motor rebuild right now because of a very bad case of overheating.  I have found that there are really, very rough castings in the water passage on the block itself just behind the water pump at the opening.  Porting this out should give you a 40% increase in flow.  Yes, it's that bad.

The water passages on both heads and on the intake runner where it mates to both heads can be ported and opened up as far as the gaskets allow and still have plenty of strenght to prevent cracking, plenty strong.  This alone will vastly improve water flow from the top-end to the bottom by about 60% IMO.  There are several parts including the T-stat housing that could benefit from some massive porting.  This is another reason why the 2000-2005 Xterras suffer from a hot engine bay aside from having the cats inside the engine bay.

This was main reason why I added the cooling vents on the hood of my X (there is a thread here for the vents).  I tried to avoid the overheating problem but the problem was bigger than I thought.

[4x4forfun]

Well, it turns out my rad was the problem.
 I picked up an all metal 2 row rad and put it in today. Out of curiosity I took the old rad apart. The top of the coils didn't really show any clogging which explains why I thought it was okay. But when I opened up the bottom I immediately saw that it had about a 1/16" of sludge and the coils were almost completely clogged. One thing I did notice about the old rad is when I took off the bottom cap I saw that the tranny cooler tube was right up against the bottom of the coils. That couldn't have helped the flow any and as a matter of fact, the coils against the tube were the most clogged. When I got done I put 540lbs of cement in the back and ran it up a long steep hill doing 55mph a couple of times and the temp needle never went over half. Tomorrow I will hitch up the popup camper with the enduro bike on it (about 1,200 lbs total) and make the same run. Last time I went up the hill with the trailer it got real hot.

[chad]

A year back I had the timing belt changed on my X along with the water pump, belts and thermostat. The radiator cracked soon after the replacement it turned out to be a faulty thermostat.
So check the thermostat

[4x4forfun]

The tstat is good as i did a boil test on it before I put the new one in a year ago and then rechecked it this weekend when I swapped the rad. I loaded up the trailer today and did a test with it and the temp gauge rose just a little over normal going up the long hill I use for road test. I am convinced I got the problem taken care of now. Just got to wait 4-5 months for warmer weather and trout season to open in the sierras. I reall don't appreciate camping in the cold winter months.

[superslidestyle]

I have these threads on my overheating problem.


http://www.sccxterra.com/smf/index.php/topic,387.0.html
http://www.sccxterra.com/smf/index.php/topic,113.0.html