have you check that the cpu cooler has been mounted correct(with thermal paste) ?

My $20 Block probably cools it better mediocre copper and all.

if the water is cold in the system and just the cpu is hot ,maybe is the water pump ?
i dont have watercool on any of my pcs,but when similar happen to cars engine ,its the pump.

Have you checked the flatness of your IHS (integrated heat spreader)? Take your CPU block off and look at the spread of the thermal paste. If the paste isn't evenly spread then your IHS might be convex or concave causing poor contact and cooling.

auski - is this a delided CPU, what paste are you running?
 
Other thoughts - You have 1 radiator on the front intake and another on the top exhaust -
You are only running the CPU on the loop correct?
You are warming up the intake air with the front radiator and gaining some heat in the case then trying to further cool the loop on the exhaust?
What happens with the side panel off?
 
Edit note - what are you using for voltages, AVX offset?

Looks to me like your coolant flow rate is too low

Your OP is a little hard to follow; so, I have some basic questions:
 
Room Temp ? --->  is needed to compute ΔT °C  (Delta T)

Pump ?

Pump speed ? GPM or LPM
 
Loop design ? (order of parts)  (1 or 2 loops ?)
 
Case ?
 
Number of Fans, size, speed used, Blow In or Out, Using Filters ?
 
Is CPU block plumbed correctly (some have an In & Out & the Flow does matter)
 
i7-9800x is Only 165W TDP & "stock Turbo is 4.5 GHz" - does not seem like you OC the CPU
 
What Voltages are used ?  Manual or Auto - (which tends to use higher Voltage than may be needed)
 
See this post for information on manually checking heat loads for your PC ---> https://forums.evga.com/FindPost/2911173
 

startekselva
what are the radiators you are using and please do share the water loop config

He said what he had for radiators and that he was using a push / pull fan config in his first post

CPU Cooler is an Aquacomputer kryos cuplex NEXT VARIO w/ Vision on a 420GTX w/ 6xML140 RGB Pros in push/pull (front mounted intake) and 420GTS radiator w/ 3x ML140 RGB Pros in push (top mounted exhaust).

Would gladly Install you GOD Loop/Block and Leak Proof...I Silicone the **** too. got quite tired of those Leaks too. Next to going to a store hardware store that has the Orings and seals that fit RIGHT.

Wow thank you all so much for the fantastic feedback and ideas. I think the problem is I just got a weak @$$ chip. Just realized the 4.5Ghz was running @ 1.422V as seen here: . I think I was so spoiled on my i7-5820k, pushing 4.7Ghz on all cores @ 1.3V (see sig). I took 4.5Ghz for granted. 
 
However, let me address a few of the (very good) points you all made:
 tramsdogmifier, GGTV-Jon, Hilguy-- yes, as a matter of fact, which I am very convinced that the Vcore of 1.422V is the culprit, having deeply contemplated the thermodynamics of the case, I am going to re-do the loop. As GGTV-Jon pointed out, the 1 radiator in the front intake is also the main radiator and in push/pull. First, I don't think there is enough intake air to begin with despite the push/pull. Second, the warm air isn't doing any good. 
 
Doomed83, jericogarcia16,--I did check the flatness of the IHS, the thermal grizzly was spread successfully (albeit I did redo it because I thought maybe it was too thick, no effect). As jericogarcia16 pointed out, conductonaut (liquid metal) is far superior and I think I will be using it when I redo the loop (described above) 
 
Cool GTX--THe virtual flow meter on the D5 Next was showing 0.8gpm. When I redo the loop (described above I will add a second D5 Next as it will almost certainly be required once the 2080 Ti's are also added to the loop. Room temp was ~19-20*C. While you point 4.5Ghz is the stock Turbo, I have concluded the i7-9800x is not designed for running on all 8 cores, unless I really did just get an awful binned chip. VCore was set to adaptive. 
 
startekselva--I did 'mess' with the VARIO. No impact. 
 
batboy88--I think you are onto something. I believe I was losing notable airflow through the sides. Will be adding gaskets to all radiators.
 
New loop:
Swapping the ML140 PRO RGB for ML140 PRO White (They have a higher RPM limit, double the static pressure and considerably more CFM than the RGB PRO). These 6 will be push/pull on the 420GTX which will now be in the top as exhaust.
 
Buying 2x 360GTX radiators and 12x ML120 Pro RGBs for push/pull in the front with 2x ML140 PRO RGBs on top (intake) 
 
ML140 PRO RGB and ML120 PRO RGB on the rear (exhaust) as seen in the pic)
 
Adding an additional D5 Next (will decide on parallel vs serial later)