Menu

$1500, Still Overheating!

This topic contains 17 replies, has 10 voices, and was last updated by Avatar Katie 8 months, 2 weeks ago.

  • Creator
    Topic
  • #661965
    Avatar
    Joshua P. McKearin
    Participant

    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 15 replies - 1 through 15 (of 17 total)
  • Author
    Replies
  • #661975
    Avatar
    Andrew Phillips
    Participant

    Ok, let’s start with the basics. How is the fan clutch? Blades on the cooling fan all ok? Radiator shroud(s) in place? What happens if you collect some of the oil and drip it onto a very hot surface? Does it sizzle or just roll around and smoke? Next, since the vehicle was sitting “for a while” there could be foreign material or corrosion plugging the radiator, or the radiator could have rotted inside. There could be corrosion or foreign material inside the engine restricting flow, maybe even just in one area causing an isolated hot spot. Why was the vehicle parked so long? Maybe this is an old problem that caused it to be parked in the first place (in this case you have no history of cause and previous repair attempts).

    #661981
    Avatar
    Joshua P. McKearin
    Participant

    ✔ Fan Clutch
    ✔ Fan Blades
    ✔ Fan Shroud

    There was no antifreeze in the oil or visa versa according to the shop. Old oil has been disposed of so cannot be tested further.

    Radiator is clear, and I actually flushed it myself when changing the thermostat before ever taking it anywhere. The old antifreeze looked good and there was no residue in the radiator. The flush was fairly clean, and water flowed very well. I tested it by plugging the lower hose port, filling it with water, and unplugging the port. With gravity only, water flowed out of the lower port very well.

    I do not know why the car was parked and do not have contact with the previous owner. Honestly, the car being parked is only speculation based on the evidence of a rodent/animal making itself a home under the intake manifold. However, I’ve heard stories of techs finding the same thing in a car with 5,000 miles on it, so take that for what it’s worth.

    #661988
    Avatar
    college man
    Moderator

    When you drive the car is there good hot heat?

    #661989
    Avatar
    Joshua P. McKearin
    Participant

    [quote=”college man” post=134784]When you drive the car is there good hot heat?[/quote]

    Heat is great at idle and up until the vehicle begins to overheat. As soon as the temperature starts climbing the heat plummets from scalding to lukewarm. Keep in mind it will idle and can be driven less than 35 mph all day long. It only overheats at higher speeds than 35 mph.

    #661994
    Avatar
    college man
    Moderator

    I would try and bleed the system again following this procedure.
    If you don’t have the spill free funnel put a pan under the car to
    catch any spillage. The cooling fan must cycle.Follow the video on
    how to bleed a cooling system.

    http://www.ericthecarguy.com/faq/what-to-do-when-your-engine-overheats

    #661997
    Avatar
    Ingvar
    Participant

    I bet you have exhaust leak into the coolant causing overheat. That it happens past 35 mph tells me it’s a pinhole that gets worse as exhaust/combustion pressure increases.
    I donno, I normally simply look for a beer foam type stuff in radiator neck but in nowadays cars you sometimes don’t even have that option. So maybe do exhaust test. They sell things for that in parts stores.

    #662000
    Avatar
    Lorrin Barth
    Participant

    Yeah, sounds like that first failed block test was giving the correct answer.

    #662001
    Avatar
    Joshua P. McKearin
    Participant

    After the first block test, a second block test, compression test and a leak-down test were both done and it passed all with flying colors. Also, there seems to be no loss of coolant.

    #662011
    Avatar
    Lorrin Barth
    Participant

    When you write overheating what do you mean? If the only symptom is a high reading on the dash gauge what does the ECU report as engine temperature?

    Another possible route is to buy your own block test kit. Sniff the reservoir after driving 35+ mph.

    Losing heater output usually means the core has ingested a chunk of air or combustion gas.

    #662030
    Avatar
    Cameron
    Participant

    [quote=”PatriotSpade” post=134797]After the first block test, a second block test, compression test and a leak-down test were both done and it passed all with flying colors. Also, there seems to be no loss of coolant.[/quote]

    We know that if the cooling systems are not bled properly you will get air pockets retarding coolant flow and then engine overheating. That issue appears to have been dealt with from your reports.

    However I would not assume, given everything you have done now and engine age/condition, that the coolant passages inside the engine are free flowing. There may well be gunk in some of the coolant passages severely retarding coolant flow through the engine so that when you get up sufficient engine rpm, and have the engine running for long enough, the overheating problem then arises. My first thought was a blockage in the old radiator but as you have it running free I really think the problem will be found inside the engine coolant passages. So I am definitely with Cap269 on this one.

    #662060
    Avatar
    Nick Warner
    Participant

    I have seen bad head gaskets pass a block test before. It happens, they are not foolproof. What you could do for confirmation is to take it to a place that has a 5-gas analyzer and have them hold the sniffer over the coolant reservoir while the engine RPM is held to 3000 or so. The 5-gas will pick up lower concentrations of gas that a chemical test won’t.

    A redneck method uses a Lisle coolant funnel and a household CO detector. Put the funnel on, place the CO detector face down in it and put a bag over the top. Run the engine and see if the detector goes off. If there is enough CO getting into the system it will trip the alarm.

    I’m leaning toward bad head gasket. You keep getting air voids despite multiple bleedings. You get it to leak when you get on the gas more, and the higher your power demand the higher you get your cylinder pressures. That’s when the leak appears. I’m with Cap and Cam here.

    #662107
    Avatar
    Joshua P. McKearin
    Participant

    Today, the shop removed the aftermarket thermostat and replaced it with a factory Nissan thermostat. They also said the water inlet hose which connects to the thermostat housing had been cut previously and was a possible source of air getting into the system. After replacing those parts, they were able to successfully bleed the cooling system for the first time. They attempted to drive the vehicle and it did not overheat, but shortly into the drive the vehicle started to “surge”. They let it sit for a while, they found that coolant had “found the path of least resistance” and made its way through the gasket separating the IAC valve housing from the bottom of the throttle body. They are now claiming that the IAC and possibly the ECM both need replaced. In order to verify the overheating problem had been fixed, the throttle body was bypassed and IAC valve was disconnected. They then attempted to bleed the vehicle again and were unsuccessful. Still overheating. At this point I have paid the bill and will have the vehicle towed to my home to continue triage myself. I have more information now on the tests that were done since I have all the tech’s notes in hand and have put them below.

    Compression Test Results
    Cyl 1: 165 psi
    Cyl 2: 175 psi
    Cyl 3: 165 psi
    Cyl 4: 170 psi
    Cyl 5: 175 psi
    Cyl 6: 165 psi

    Leakdown Test Results
    Inconclusive and Cyl 2, 3, 5, and 6 would not hold pressure due to carbon buildup on intake valves

    Do these test results change the likelihood of a head gasket issue? And also, if this was a head gasket issue that was keeping them from being able to bleed the system, would there not be an obvious loss of coolant? And what explains the fact that they were finally able to bleed the system until the throttle body/IAC valve gasket failed?

    #662110
    Avatar
    Bluesnut
    Participant

    Assuming the radiator is not partially clogged in spite of the flush you might consider this. I don’t know if your vehicle is equipped with it or not but many have an air dam underneath the lower radiator support. The purpose of this strip of plastic is to cause air to pile up in front of the A/C condenser and radiator and which then increases airflow through the radiator.

    These air dams often get knocked off due to curbs, road debris, wildlife on the highway, etc. If the air dam is missing an engine can idle all day long or run at slower speeds without overheating at all but once at highway speeds it can overheat; often severely.
    A missing air dam can cause a 30-40 degree variation in engine temperatures and it’s one of those sight unseen and seldom thought of parts that can be a real problem.
    If your car is not fitted with this then maybe back to the partially clogged radiator theory. 🙂

    #662190
    Avatar
    Joshua P. McKearin
    Participant

    I checked to make sure all of the plastic shroud and other parts around the radiator are present. I did not see anything that was missing. How do I test the partially clogged radiator theory without installing a new radiator?

    #662203
    Avatar
    Lorrin Barth
    Participant

    [quote=”PatriotSpade” post=134990]I checked to make sure all of the plastic shroud and other parts around the radiator are present. I did not see anything that was missing. How do I test the partially clogged radiator theory without installing a new radiator?[/quote]

    So far as I know that is how. However, as much as you or your mechanic have been into the engine replacing cooling system parts, if there were sufficient deposits to plug the radiator I suggest they would also be evident elsewhere.

    Another possibility I can think of, in this era of cheap disposable radiators, is that the vehicle at sometime in the past needed a radiator but a previous owner cheaped out and purchased one of insufficient capacity. Check if the radiator looks surprisingly thin or small.

Viewing 15 replies - 1 through 15 (of 17 total)

You must be logged in to reply to this topic.

Loading…