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HT4100 4.1, 4.5, 4.9 Discussion, Is 104C too hot for a 4.9L 1994 Deville? in Cadillac Engine Technical Discussion; Originally Posted by tony1963 Some guy with a can of beer in one hand and a remote control in the ...
  1. #31
    youbetcha77's Avatar
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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by tony1963
    Some guy with a can of beer in one hand and a remote control in the other knows more than the engineer who designed the engine.
    What engine doesnt have aluminum in them now a days?

    Blaze

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    Question Re: Is 104C too hot for a 4.9L 1994 Deville?

    How about running the car without a thermostat to stop high temps in the summertime? or will that harm somthing?

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    tony1963 is offline Cadillac Owners Member
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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    By George, another scientist!

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by stephen j s
    How about running the car without a thermostat to stop high temps in the summertime? or will that harm somthing?
    Then the engine may not warm up enough to go into closed loop which would make economy suffer.

    Blaze

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Running without a thermostat may cause as many overheating problems as with one that is bad. The thermostat is a calibrated orifice in the cooling system, it restricts coolant flow so that it doesn't pass through the radiator too quickly, not passing off as much heat as it should.

    For example, if the radiator as designed with a proper factory spec'd thermostat is expected to give off 50000 BTU's of heat in a normal pass of the radiator, and you make the coolant flow FASTER, it may not have sufficient time to pass that heat off, and may only pass 25000 BTU's, therefore the additional heat is sent back to the engine to be heated even more by the engine, which is expecting to have the coolant down to a certain temp before it comes back for more. These numbers are purely fictishous, I have no idea what they actually are. Only a GM Cooling system engineer would likely know.

    As for not going into closed loop, my experience is coolant temps need to be below 150, possibly even cooler to have an effect on closed loop operation. I suspect GM engineers knew people would mess around with cooler thermostats and ensured that they would still go into closed loop even with a cooler one to keep emissions somewhat in check.

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    tony1963 is offline Cadillac Owners Member
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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    The speed of the coolant going through the circuit has nothing to do with the heat transfer abilities.

    Keep in mind that if it runs "too fast to lose heat" in the radiator, it consequently runs too fast to pick up heat in the engine.

    Speed of running coolant is not relevant.

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    And why are Cadillacs delivered to Europe have an improved and optimized coolant system (and reinforced transmission) ?


    Because we have a very different traffic situation. A regular Cadillac imported from the States, without improved radiator will overheat on our autobahn.

    These motors are designed to drive from eastcoast to westcoast but not for the daily overkill on our fu..... autobahn.

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by tony1963
    The speed of the coolant going through the circuit has nothing to do with the heat transfer abilities.

    Keep in mind that if it runs "too fast to lose heat" in the radiator, it consequently runs too fast to pick up heat in the engine.

    Speed of running coolant is not relevant.

    uuhhh.....wrong.


    tony and NODIH....I hate to break the news to you but the speed of the coolant flow DOES have something to do with the cooling efficiency. Basically...the faster the better. Any engine cooling engineer in the world can verify this for you.

    Trust me, the coolant has plenty of time to "give up heat in the radiator" and "pick up heat in the engine" no matter how fast it is moving.

    It really is an old wives tale (that is totally false) that slowing down the coolant helps the cooling system. I think that got started eons ago when hot rodders started revving stock engines past where they (or their water pumps) were designed to operate. As a result the water pumps cavitated, stopped pumping and the engine overheated. Someone got the idea to slow down the water pump with a larger pulley on the water pump and the engine quit overheating. So....they invented this idea of "slowing down the coolant so it has time to pick up the heat and give up the heat". Trouble is, the reason the engine no longer overheated was because the water pump was pumping again and not cavitating like before....it had nothing to do with speeding up the or slowing down the flow rate.


    Theoretically, it is easy to argue that the mass flow rate of the coolant doesn't matter. Trouble is, that doesn't take into account the efficiency of the radiator and the "scrubbing" effect of the high velocity coolant inside the engine.

    The greater the temperature differential across the radiator (the radiator fin temp to the air temp) the more efficient the heat exchanger is. The faster you move the coolant the higher the temp of the fins on the cold side so the rad efficiency goes up and the system cools better.

    Inside the engine, at the hottest spots, bubbles can form on the hot surface...called nucleat boiling. Those microscopic bubbles on the hot surface tend to isolate the coolant from the surface and reduce heat transfer. Faster flowing coolant scrubs the bubbles away and promotes more heat transfer to the coolant thus reducing engine temperature. High flow is good.


    Modern engines move the coolant at a very high rate. The higher the output of an engine the faster the coolant flow. The coolant pumps are designed for very high flow rates at high efficiency so as to not sap too much power from the engine.


    It is not desirable to run without the stat in general because of warmup and such. With the Northstar engine, in particular, the stat is an integral part of the flow control of the system and the sytem will NOT work correctly without the stat in it and it will NOT have the maximum cooling efficiency.

    Having said that....with the 4.9 engine the stat is a fairly simply device that simply controls to a temp and it is NOT part of the integral flow control of the system. Removing the stat will usually help the cooling of the system due to the increased flow in a 4.9. This is true only for a maximum effort cooling situation where the stat is fully open anyway. Removing the restriction from the system will help slightly if that were the only situation the engine had to deal with.


    NODIH, the problem with your reasoning is that you forgot to include the part where a much greater volume of coolant would go thru the radiator in the same time period. True, per your example, on a single pass an individual slug of coolant would give up less heat in the radiator but without a given time interval more slugs of coolant would pass thru the radiator with a faster flowing system thus the total heat transfer would be the same in that simplistic example.

    As I indicated earlier, that slug of coolant would pass thru faster and would give up less heat and would exit hotter....so the end fins would be hotter in this case than in the slower moving coolant case. THAT would improve the heat transfer capability of the radiator by increasing the delta in temperature between the fins and the air coming thru it....thus the overall cooling efficient DOES get better with faster flow.

    Trust me, I have done lots of engine cooling development and have seen it proven over and over that the more flow the better. It isn't even up for debate. Slowing down the coolant or orificing the system is NOT the correct thing to do for cooling efficiency. If someone makes a mod like that and it "improves" the cooling of the system then they had something terribly wrong elsewhere and they are not fixing the problem by slowing down the coolant..!!

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by tomtom
    And why are Cadillacs delivered to Europe have an improved and optimized coolant system (and reinforced transmission) ?


    Because we have a very different traffic situation. A regular Cadillac imported from the States, without improved radiator will overheat on our autobahn.

    These motors are designed to drive from eastcoast to westcoast but not for the daily overkill on our fu..... autobahn.

    uhh....wrong.

    Export cars get the same cooling package and transmissions as the domestic cars do. I hate to make you think that your car is "nothing special" compared to the US cars....but....it isn't.

    High speed cooling on the autobahn is actually not that stressful. True that the engine is under high loads and high speed but the vehicle is also moving very fast and the ram air at those speeds offsets the additional load. All the cars, whether for the US or Europe, are cooled for high speed operation. If you think the Europeans have a monopoly on high speed driving then you have never driven across Texas or in the desert south-west of the US...or across Montana. Speed limits or not that is some very desolate country with some pretty straight roads and the speeds rival anything on the autobahn....LOL.


    The hardest cooling situations can be the city traffic, stop and go, 105 degrees F in Phoenix, Arizona that the US cars have to contend with on a daily basis....or city traffic in Florida at 100 degrees F and 100 % humidity and full AC load....or flat out from Baker California to Death Valley at 110 degree F ambient.

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    Exclamation Re: Is 104C too hot for a 4.9L 1994 Deville?

    ---------Hey not for nothin guys i ran my cad today without the stat and it ran in temp zones like ive never seen befor! in a good way!
    With the stat: it ran about 195-225
    without the stat: about 175-215 (whille driving with the air flow helpin}
    -----But it did reach to 225 in traffic due to the shitty fan run time!
    Thus my cooling battle carrys on. I think next thing is to get the override swich. Bob is mostdef right thought,.
    and yes i had already put in a 180 stat and it dident do dick

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by stephen j s
    How about running the car without a thermostat to stop high temps in the summertime? or will that harm somthing?
    A cooler stat (say 180 instead of stock 195) will bring highway temps a few degrees down. Same thing obviously with driving without stat. But when it comes to 200 plus any stat would be open anyway and does not affect the cooling performance. Now things more depend on fans. Perhaps, removing stat will increase the flow but I really do not think you'll get any dramatic change.

    I have installed a 180 stat and now highway temps are 186-188 instead of 194-196 before (with stock stat). But in traffic it is 220 plus anyway untill the fans kick off. I change the stat intentionally since I have EGR related spark knoch when engine is hot, so some8-10 degrees make some difference and at least make me feel better.

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    I agree with illumina

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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    I would still like to know why these engines were designed to run so hot. Also why the constant temperature fluctuation from 195 to 233 (stop and go driving) is acceptable. Think of all that expanding and contracting between the aluminum block and iron heads - 2 materials that have different rates of thermal expansion. Sounds like the head gaskets have alot to deal with yet these motors easily pass 200K miles....

    I wish [CENSORED] was still around. I have a week's worth of engineering questions about the 4.x series.

  14. #44
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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Quote Originally Posted by Sevillian273 View Post
    I would still like to know why these engines were designed to run so hot. Also why the constant temperature fluctuation from 195 to 233 (stop and go driving) is acceptable. Think of all that expanding and contracting between the aluminum block and iron heads - 2 materials that have different rates of thermal expansion. Sounds like the head gaskets have alot to deal with yet these motors easily pass 200K miles....

    I wish [CENSORED] was still around. I have a week's worth of engineering questions about the 4.x series.

    Why? Emissions, mileage. The hotter an engine runs, the more efficient it operates. It's really that simple. the hotter they can get it to run without destroying components and gaskets, the better. for both power and fuel efficiency.

    As far as the temp between 195 and 233 - that range, by percentage, is no different than any other engine out there. They all run a little bit hotter and a little bit colder under certain conditions. Even my own work truck, a 2003 Sonoma with a completely iron 4.3 V6 fluctuates at approximately the same temp range all day. It seems everyone's a little more paranoid with a digital coolant temp display at their disposal.

  15. #45
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    Re: Is 104C too hot for a 4.9L 1994 Deville?

    Actually watching my analog gauge bounce around is much more dramatic!

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