My 90 Q45 overheated today for no apparent reason. This is the second time it overheats within a week. After the first time it overheated, the engine is much more noisier with a harsh rasping sound at low speeds. Prior to this the car ran smoothly and quietly. I've had to top off the radiator with water more than once after the first overheat. There is no apparent leak in the cooling system but I did notice water mixed with oil in the oil dipstick. Also the car is idling now at about 1200-1400RPM.

Are these symptoms normal after a car overheats? What could the harsh rasping noise be? The engine does not feel nor sound as refined as it should be-why? What does water mixed with oil on the dipstick imply? What are the possible solutions?

Your help is greatly appreciated.

Sorry to hear the bad news. But for the sake of your investment in the car, park it until it is repaired.

My guess is blown head gasket. But I don't know from Adam. Water in oil is not good.

I am sure the professor or Q45 Tech will have a better diagnosis.

Well you must have the radiator [checked for leaks [pressure test meter] and then the coolant for the presence of combustion gases [chemical solution which changes color]. Have a compression and leak down test performed.

If you have a blown head gasket you have a warped head.

Never seen but one blown head gasket on a Q [very rare]

Probably a leaking penum hose allowed all the coolant to pump out under the plenum....which overheated and caused knock sensors to fail from melting [cracks?].

Running a Q engine in overheat [for any length of time above 250F] is a sure way to get to spend $6,000.....they never are the same after 15 minutes of abuse.

Find an expert to deal with it..............Don't crank it again without the expert being present......coolant in the oil will destroy all the bearings in very short order they will have to be replaced along with wrist pins.

checked radiator [checked for leaks [pressure test meter] and then the coolant for the presence of combustion gases. Had a compression and leak down test performed. Turns out problem was with radiator. Passenger side tank has 4-5 inch hairline crack. So I will need a new radiator. Any suggestions?

First, I would try to find an aluminum radiator. I replaced my 94Qs with a brass and it's works but I think an OEM would be better. I bought mine from "Halks Radiator" on Cave Creek in Phoenix for $180 which is less than half the cost of a new one.

Get an OEM radiator... did anyone figure out how the water got in to your oil and the cause of the additional engine noise you heard? I wouldn't put $370 (whosale from Scottsdale) into a new one until you know if the engine is going to hold up. If you've warped the heads, It's probably time to find a good take-out engine from Japan.

Heath

I had a crack like that in the radiator of my previous Q. I'm almost certain I got it from the dealer that took a shortcut in replacing my A/C compressor and drier by doing it without removing the radiator. Naturally the fatigue crack from their ham handed work took about 4 months to start leaking, so I had to eat it. Fortunately it never overheated, just leaked, so I didn't have the engine damage you've got. Good luck!

Make sure the crack isn't a Compression Crack! ie: blown gasket causing excessive pressure in the radiator.

The water in the oil should be a concern, & the rough running etc, all point to a cylinder being bad. Hope I'm wrong.

Everything has checked out fine. Engine runs smoothly. But I still need to find a good radiator. I don't want to pay for alot. I found a oem replacement aluminum radiator on the web for $189. I also found a shop that is willing to make a custom radiator out of more traditional materials for same price. What do you guys think?

Best if you stay with the Alloy radiator as with the brass one, you may incur more electrolosis.

If you had the correct coolant in at ALL times, then that shouldn't be a problem, as Volvo has had that combination for years in their old V6. If you didn't keep the coolant up to them, you soon had a hole in the Block (ouch!)

Please post the site where you found the 189.00 radiator.

site where I found radiator for $189 is carradiator.com.Chally please explain electrolosis.

Put simply, it's where the electrical currents, in the coolant, eat away the metals inside the engine.

If a radiator replacement is required, good idea to change the anode pipe [that ties the drivers side 2 hoses together] and the thermostat and cover pipe as these are made of metals that are designed to corrode first, saving the radiator.

Dennis can comment more on this, but I've heard bad things about aftermarket radiators.... It may be adequate in most situations, but on the margins not be able to perform as well as OEM. In AZ heat I'd get the best cooling system possible...

Heath

Stick with OEM for fit and quality. Do the aftermarkets have the sensor in the lower left section of the radiator?

I would not gamble in AZ...I felt the risk of engine damage in the AZ heat wat too high with a non-OEM unit. I have, of course, been happy with the OEM unit...no overheats at all this year, even while climbing Pima road in 4th with the AC full blast on a 115 degree day.

If a car needs OEM bulbs to make the diagnostic system happy, it would be safe to say it probably requires an OEM radiator (or whatever else...).

Q45tech wrote:If a radiator replacement is required, good idea to change the anode pipe [that ties the drivers side 2 hoses together] and the thermostat and cover pipe as these are made of metals that are designed to corrode first, saving the radiator.

I'm curious; do you know what metal the anode pipe and thermostat/cover pipe are made from? Magnesium would be about the only common metal that would be anodic to aluminum. I've never gotten into the cooling system yet so I'm not familiar with these parts. I wasn't aware that Infiniti uses sacrificial fittings like this. If this were the case, the magnesium parts would corrode very fast due to small anode/large cathode ratio.

Remember the components are not pure aluminium but mixed aluminum alloys and zinc amalgam coatings....the radiator is floating not in electrical contact with any chassis or other item isolated by rubber. The joining pipe is bolted to the engine block and isolated on both ends with rubber hoses.

http://www.sic.shibaura-it.ac.....html

Commercially pure magnesium -1.75 Magnesium alloy (6% Al, 3% Zn, 0.15% Mn) -1.60 Zinc -1.10 Aluminum alloy (5% Zn) -1.05 Commercially pure aluminum -0.80

If ANY part of the cooling system shows corrosion, you are not changing the antifreeze solution enough or are not running any. That is a real problem with using low content antifreeze mixes (like 80% water, 20% A/F)

Houston has pretty horrible cooling demands on a car--the high humidity and high temperatures really load up the A/C system so that a typical 95F day means 110F road level temp into the radiator, and very high A/C loads, resulting in a total cooling load much higher than Arizona at 120F!!

A OEM capacity replacement radiator from Radiators.com (all copper) works GREAT in my wife's 92 Q45a.

I run 50% A/F in my cars for the corrosion protection, change it bi-yearly using distilled water, and have never had corrosion in one. Hers leaked at the tank gasket one day , and I did not want to risk an inopportune loss of coolant overheat/engine meltdown for a $200 radiator replacement. Our rules are: Wife is to drive to safety no matter what, if possible. Cars are replaceable, she is not. So, I keep it as close to 100% reliable as possible. Just had all hoses, belts, idler bearings, water pump, plenum hoses, valve covers, chain guides, etc replaced. An excellent independent shop here did the work .

I was very pleased (I am extremely 'fussy' about my cars) and you could not tell they had taken everything apart it was put back so neatly and completely. Absolutely perfect job.

Copper is about the worst choice in an all aluminum engine as AF is designed for at the worst for an iron engine and aluminum radiator.

Mixing metals and water is not a good idea.

Very simple test: Use a voltmeter, one lead on the aluminum filler neck the other lead into the AF/coolant an inch - any voltage even 0.1 volt means electro chemical reaction is occurring!!!!! Silently eating away at something.

You must know what the chemical make up of the additives in AF is as there are a half dozen formulas and each does somethings well and others BAD.

Truckers who use $2,500 radiators check the additive levels every 6 months and adjust the PH......they can get 500,000 miles out of a unit or at least 6-7 years.

Why does one Q idle at 176F and another at 185F and another at 200F in 100F ambient at exactly the same rpm, same AC, same gasoline, same spot after 15 minutes!

98% is the radiator and thermostat [slight variance in opening amount and temp but spec is +-2F].If the engine is running at the same rpm the injectors are opening the same amount so the same amount of heat is being generated.

Important that you test the real temperature of your Q as the inside gauge won't tell you anything in the 176F-200F range.......you could be on the ragged edge of overheating and not know it till its too late.

Aside from not changing oil, overheats are the number 2 engine destroyer.

We give owners 2 options: a factory rad that will perform as new [and probably last 8 more years] and a cheapo $200 rad that may only deliver 85-90% and last 4 years. Most don't have overheats at first.But I can assure you [from tests] that there is a 10F difference [brand new] in severe conditions but since the warranty is only 12/12k we have never tested a used old cheap vs a new cheapo.

I cannot speak from experience about all aftermarket radiators. There probably are some that are less than equal to the OEM unit.

What I CAN say with great certainty that the replacement radiator I purchased from Radiators.com was AT LEAST equal in heat rejection capacity to the OEM. It had more fins/inch, higher fin height, the same number of tubes and tube diameters, and the same finned area, and it is brass--a far better radiator material than aluminum. Aluminum rapidly develops an 'oxide' coating on all unprotected surfaces and that oxide layer is a very good heat insulator. It is all but impossible to prevent that oxide layer from forming since it takes only seconds to develop when bare aluminum is exposed to air. In "Real World" service conditions, brass is significantly better overall.

Please note I am not suggesting the OEM unit is a poor or inadequate design, just that there are far less expensive, high quality, OEM or better capacity aftermarket units available.

Radiator design and manufacturing for automotive service is not 'high tech'. The science is well developed and well proven and widely known. For internal combustion engine cooling, bigger is better, brass is better(performance wise), more fins/inch is better. It is when designers 'squeeze' the physical and thermodynamic limits (to reduce cost, weight, space) that things get complicated. Nissan has not done that on the Q45. The OEM radiator is amply sized and robust. They fail when people do not properly change the coolant or keep the exterior clean. Mechanical vibration also takes it's toll - rough roads and road salt are hard on lots of things. Heat-up/cool down cycles take their toll. 'rubber' gaskets get harder with age.

I contrast the Infinity 'robust' design to Mercedes Benz design. They used to publish (prior to about 1990)charts in owners manuals showing coolant temperature plotted against road speed and outside air temperature. The 'normal' coolant temperature at 100F and 120 MPH might be 260F!The new designs since 1991 often run 220F or higher in normal around town driving-mixed stop and go. They run at 20 psi, and still had to put very large (10qts+) secondary 'coolant recovery' reservoirs under the fenders to contain the boil-over it is so bad. Even newer models often run 240F around town.

The Q45 is very generously cooled by comparison. The engine damage events on Q45's happen from total loss of coolant from leaks, not 'overheating' caused by undersized radiators.

Agree but the discussion was COPPER ["(all copper]" your quote] not Brass which is an entirely different compound.

We get so many overheats in Summer [from poor maintenance] that I have devoted weeks to studying the problem.The easiest thing is to LOG DATA [coolant temperature] for 30 minutes in 1 minute intervals in Park Ac on, then drive on the interstate at 60 mph and log data till it cools or turns to a stable point.

What most don't understand is that 25 HP at most is created at 60 mph and less at idle.....at 120 mph 120 HP might be required to move the car through the air.......double the speed quadruple the HP required at minimum!

80 mph ac on in 100F for hours is pretty stressful on any cooling system....but not necessarily more so than zero mph in drive in 120F street airNever been able to log data at high speeds to determine the efficiency at 100 or 120 or 150 mph but supposedly they did laps in Arizona at 155 mph but whether that was 3 minutes, 5 minutes, or 10 minutes is unknown.

The problem again is the Q ecu uses coolant temperture to adjust ignition timing so any temp at that sensor in excess of 194F is detrimential to performance, efficiency and gas mileage.......you gotta known what's happening inside the coolant circuity. 1.0 F is extremely important if that 1.0F throws you over the edge into the start of retard [next one occurs at 200F, then 205F, then 210F, then finally 215F.

The Q only uses a 0.9 bar pressure cap~~ 13.25 psi so 260F is it....the question is will the under plenum hoses or others hold 12 psi after years of use!