$1500, Still Overheating!

This topic contains 17 replies, has 10 voices, and was last updated by Katie Katie 10 months ago.

  • Creator
  • #661965
    Joshua P. McKearin
    Joshua P. McKearin

    2001 Infiniti QX4 4WD
    3.5L V6 (VQ35DE) 190k miles
    United States

    Things which have been replaced:
    Thermostat, Water Control Valve (second thermostat), Water Pump, Radiator Cap

    Tests ran:
    Chemical Block, Cooling System Pressure, Compression, Leak-Down

    I bought the vehicle after inspecting it personally and finding no major issues outside of a coil pack issue. A couple days later the vehicle overheats after being on the interstate for 2 miles. Vehicle will idle without overheating, and can be driven less than 35 mph without overheating. I replaced the main thermostat, did not resolve the problem. I was afraid I did not bleed the system correctly, took it to a local mechanic. No change after bleeding cooling system, so he did a block test which “failed” but he was perplexed due to no coolant leaking and no mixture of oil/coolant. Suggested I take it to a Nissan specialty shop. The specialty shop ran chemical block test and vehicle passed. The specialty shop stated that after bleeding cooling system using Varajet system, the vehicle would get approximately 5 miles interstate and overheat. They manually bled the system and found major air pockets. They then ran coolant system pressure test and compression test, both passing with flying colors. We replaced the water pump, did not fix the issue. Decided to replace the water control valve (second thermostat for the block). The water control valve sits underneath the intake manifold. They found dog food underneath the upper and lower intake manifolds. It was then obvious the vehicle had been sitting for a while. They also found a leak at the block water outlet (see attached picture). They cleaned that mess up and replaced the block water outlet gasket, water control valve, and bypass pipe gaskets. Still overheating. The specialty shop is perplexed.

    EDIT: Also adding pictures of the cooling circuit for reference since it’s an odd system.

Viewing 2 replies - 16 through 17 (of 17 total)
  • Author
  • #662219
    Diman Todorov
    Diman Todorov

    Hi spade,

    I have had a car with a similar issue before – thrown thousands at it to fix mysterious coolant leak. In my case I did have the head gasket (2 of them – V6 engine) done, along with water pump, thermostat etc and it was still over-heating.

    Speaking of which, you should replace wire clamps with worm screw ones.

    The problem was only diagnosed correctly after an unrelated engine swap (lost oil because of failed crankshaft seal). Turned out it was a metal coolant pipe which had rusted through – should have cost $15 to fix it!

    The moral of the story is: the coolant is going somewhere. The coolant is colored intentionally so that leaks are easy to identify. Find out where all the cooling lines go, take a flashlight and get under the car. Look at every inch of coolant piping for pink spots / gunk.

    Look for the simple fixes first, before you go for expensive stuff:
    * radiator cap
    * o-clamps
    * piping

    I don’t know how much you love your car but for a temporary solution you can try that radiator sealant goop that goes in the coolant. Mechanics will say that it will clog your radiator and may make things worse but it may be a viable fix depending on what you’re planning to do with the car down the line. For me it didn’t make any difference – good or bad.


    Wow, the original post was a few years ago I see but alas, I have a 2001 QX4. Coincidentally, it’s a little over 191K on miles and has been periodically overheating during the summer months. Usually I’ll find that I’m a little low on oil or radiator fluid. Now that it’s cooler out, I still swear it sounds like my oil is boiling. Guage isn’t showing overheat but a friend mentioned my motor smelled hot a couple weeks ago too. He’s a hobby mechanic like myself and has some knowledge I do not. I just changed the oil and filter myself about a month ago and I don’t drive much. However, while I haven’t completely read through all the comments, which I realize I really should, I can’t help but find myself wondering if it’s an oil issue? Like the oil pump or sending unit? I do notice an odd smell from my exhaust when I start driving after first start though. Have been wondering if it could be a clogged catalytic converter but haven’t got my lazy but under there at night after a good drive to see if it’s red hot, does that even really work? Anyway, the motor still sounds pristine and I really like the vehicle so would like to repair it if possible. No heat issues inside cabin but there does seem to be a bit of a loss of radiator fluid from time to time and my reservoir doesn’t seem to want to hold anything at all. I’m guessing there’s an unforeseen crack in it somewhere but I haven’t dug in that deep yet. These things are a bit more complicated than I really think they need to be. But I guess that’s just how it goes nowadays, all about the money right?

Viewing 2 replies - 16 through 17 (of 17 total)

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