Garry_W_C5_1999

Just changed a 42Kmile LS6 out. Was running just fine. Purpose is for USCA/CAM-S racing. I installed an LS3 525HP Crate Motor and my park/idle temp is <210 on super hot day with >100F ambient. But when I start driving it eventually climbs to 230-234F and struggles to come back down untill I stop again, and then it recovers. This can be country roads or highway, it doesn't matter. I think it is an airflow issue where the 110 extra HP is too much for the non fan-forced level of air flow. I installed a Ron Davis high capacity radiator and I cleaned the AC condensor core during the install. I checked and changed the thermostat when I discovered this issue, both old and new worked in a boiling water pot (with gauge). I also now have trackspec hood vents. I have tried with them blanked off and open. No difference. I was wondering if I had affected the air pressure balance into the radiator. Definitely seems to be not enough air flow without fans. Even a problem on the highway. Max it gets to is around 234F. Ambient is very hot (90-100F) and fairly humid. I was not expecting this issue. My front radiator airdam is in decent shape. I have cleaned the AC condensor with a brush vacuum ad then reverse blast of compressed air, it is clean. Fans work as instructed. I am wondering if a better quality radiator air scoop, like the Big Mouth will help. If that doesn't then I am running out of ideas. Engine was tuned by local tuner. I just got it back on friday, it made 460Hp at the wheels. I was not at the dyno, he reported no temp issues and no retarded timing. I have some engine retard that is going on as well under moderate/hard acceleration. I will be taking it back to sort that out, but I'd like to get this cooling issue resolved. Anyone experienced and solved this. I don't think it is airlock as the LS3 (like the LS6) has an upper small bleed hose piped back to the top of the radiator which also then has a hose to the expansion tank.

Garry_W_C5_1999

Problem is solved, so Posting this as I am sure someone else will bump into this issue.

The problem was with the port size of the two fittings on the passenger side radiator top section on the new Ron Davis Radiator. One is the return from the top of the block and is a small hose (1/4"), the other is the expansion tank feeder hose and is a bit bigger (3/8"). I noticed that the expansion tank had a lot of turbulence (flow) goig through it. This bothered me as, at the time not knowing what the radiator tank looked like inside, it seemed wrong. I opened the old original radiator and these ports go to a closed box and are tiny openings (1/16" and 1/8" maximum I estimate). So I put some vice grip clamps on the hoses to partially close them off, in particular the large one to the expansion tank untill the flow into the expansion tank was pretty low. I went for a drive and the temp was rock solid at around 198-201F under all driving conditions. I am baffled as to why Ron Davis would send me fittings with such large porting. I will call them on Monday and discuss. A decent portion of the coolant flow was shortcutting across the top of the radiator through the expansion tank.

brplatz

I would argue that in 100 degree heat, 235 is not an unreasonable temp, especially with a built engine.

I am having issues with mine, but the engine is stock and she keeps hitting 270

stingray76l82

If the engine is stock . I would change the radiator out. I changed mine out after new flush and fill still got hot. I decided to change the radiator out since was 12 years old . The guy who had it before me did track racing. Changed it out no problems since. It was 105 today here in Big D and with traffic I was 198 to 205 .

Garry_W_C5_1999

[QUOTE=stingray76l82;1592698874]If the engine is stock . I would change the radiator out. I changed mine out after new flush and fill still got hot. I decided to change the radiator out since was 12 years old . The guy who had it before me did track racing. Changed it out no problems since. It was 105 today here in Big D and with traffic I was 198 to 205 .[/QUOTE

Thanks. I am not sure if you missed my second post above, but I solved the problem as described.

stingray76l82

A little slow on the uptake.

Garry_W_C5_1999

Ron Davis (owner) called me today, in response to my message with the receptionist for someone in tech sales to call me. I shared the sketch below. He said he would send me some fresh fittings with small bore. He said he understood the explanation and would look into the design. He said they get proprietory specs from GM that he cannot share regarding port sizing and flow/heat calcs. He is familiar with the stock design and has one in house. He will follow up on the feedback. Very good service from Ron to call me and discuss. He is not sure why others have not experienced this. So more to come in a bit.

Attached is my explanation of the system and problem I experienced.

danh52

When you get the fitting with the reduced flow would please post a picture?

I have the same rad and LS3 conversion and might want to do the same mod. I drove in 75 deg weather today and at prolonged idle (heavy stop and go traffic) the temp was 208 deg and once moving dropped to 197-198. With a little more aggressive driving it stayed at 198. We will be getting warmer weather later this week, 88-89, I'll see what I get then in similar driving.

In a previous life I designed cooling systems, including surge tanks, for diesel engines and even for a 450hp DD engine the vent from the rad was only 1/4". It makes sense that significant flow could be bypassing the rad. Thanks for the heads up on this.

StuntHeavy

Interesting find. Thanks for sharing.

I'm running into similar issues (Fine idling all day, hot when cruising). Mine my be related to my intercooler placement, but I hadn't even thought of checking for excessive flow through the overflow tank. Thanks for the idea

Garry_W_C5_1999

New Fittings arrived for teh Ron Davis radiator. Attached are photos. I also cut open the old radiator tank body to get better access to the port size on the old fittings. They are both 1/16" on the old stock radiator. New fittings are also 1/16".

Garry_W_C5_1999

Posting one final update.

All of the above tweaks in prior posts contributed to stabilizing "running hot" condition during all driving conditions except autocross. Autocross (low speed with high engine intensity) would still cause intermittent running hot (>225 degF and coolant spill). I believe this problem is from inadequate airflow at low speeds with high engine intensity, related to the new high hp ls3 engine. I installed a Dewitts high cfm fan kit and ran some jumper wires from the fan relay coil signals to toggle switches installed in the cab to force them on when I do autocross runs. I have now raced for 1.5 months with no issues with this setup, including hard back to back repetitive runs on a hot days, many times over the last 1.5 months.

During the diagnostic period, before resolving the issue, I tried a 176 degF thermostat, 3 small pilot holes drilled in it, as well as a ball valve in the cab heater recirc line (to limit bypass flow). These did not solve the problem. The high cfm fans, set to be on (low speed and high speed) during autocross runs have solved the problem for me. It was an airflow heat exchange capacity issue.