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My car has an edelbrock carbed 355 and starts and warms normally. After it warms up and I am on the expressway or cruising the factory gauge (sensor in passenger head) gets to about 1/2 and then will get to about 3/4 of the gauge and move between 1/2 to 7/8 of the gauge almost randomly while the after market gauge (manifold) stays about 180 where my thermostat is set. When I come to a stop the aftermarket gauge slowly creeps up to 210 where the fan comes on and the factory gauge drops quickly to under 1/2 then stabilizes about 220 when the fan is on. My fan switch is in the other head and is designed to come on at 211 and it does when the after market gauge reads 210.
If I start cruising again the aftermarket gauge goes down the 180 again and the factory gauge stays under 1/2 for a while then goes back over 1/2 again and begins its oscillations between 1/2 to 7/8 again.
EDIT*************
To make it clear I was not getting proper circulation during warm up due to my heater core being bypassed and for some reason the internal pump bypass not doing its job. So the head got hot and did weird things before the thermostat opened. More to come.
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This started late last year on my last ride or two. Before that I replaced the water pump only because I was already in there replacing some other stuff
The car has no running issues.
Things I have checked.
Air dam is in place
Lower and upper hose are new and lower has a spring.
New temp sender for gauge.
New thermostat
System bled
I am checking for exhaust gas in the coolant today
My factory gauge used to do that until I replaced the sensor in the head and cleaned the contacts behind the gauge. It's a lot more stable now, though it does hunt up and down randomly once in a while still. I suspect I need to clean the gauge internally.
Spent some more time with the car yesterday. I could not detect any exhaust in the coolant using a kit I borrowed from a friend. Took it on a bunch of passes and still nothing. It was acting a bit better but I did not get a long cruise in. Hopefully this weekend I will get some time with it.
Can anyone think of a reason using the "heavy duty" water pump with 8 fins instead of the stock 6 fin model would give me issues?
After every run around I got out the IR temp gun and both sides of the engine were exactly the same. Even though the gauge says above 240 on one head and the fan switch that comes on at 212 is not activated.
Another update
I disconnected the gauge and ran a multi meter while cruising the gauge is accurate.
I swapped to a normal water pump no help
I removed the thermostat and the two gauges synchronized everything is good now except I have no thermostat and I run at 150F while cruising. So the thermostat is closing while cruising and the head is heating up.
The only thing I can think of now is I some how messed up something on my intake gasket install as this happened after so I ordered a new set and I will remove the manifold and check everything.
If that reveals nothing I am not sure what I will do. I have tried an AC delco thermostat (motorad) duralast (motorad) and stant super stat. I still have a gates (motorad) thermostat sitting in a box.
So at what temp are the fans actually coming on.
Harbor Freight sells a inexpensive "laser temp gun" and it will give you a much more precise reading.
Aim it right next to the fan switch.
Link = https://www.harborfreight.com/infrar...ter-93984.html
They have others but this little bugger gets good reviews.
A 180* thermostat and a fan switch set at ether 180* or 190* is what I would do.
If your fans are coming on any higher than that you have a problem at that point.
Those two things must work together.
I use this. Its totally adjustable and has worked for me for over 6 years now.
Just do not use there instructions.
I have a very simple and safe way to install them.
I have two,on separate circuits controlling two fans.
I painted them black and use small black wire loom on everything.
That way there out of site if you want.
My fan comes on at 210 which is where I want it and the aftermarket gauge confirms with the ir gun. The problem is the thermostat closes while I am cruising and the temp in the head increases until I slow down and the rest of the system catches up.
Well I finally got it all worked out. I added a small coolant bypass from the manifold to the pump for the heater core delete like on Vortec blocks and everything is fixed. The new water pumps built in bypass must be different from the old one or something but no more issues.
I took a look at edelbrocks manual for my manifold the port I used was this one circled. As you can see my fix is super UGLY. I did it with random stuff I had int he garage as a test. If everything stays good for a week I will order some nice fittings and fix it up proper. I am still not sure why with my old pump I had no issues and two new pumps my block acts like a 96 and up block and wants a bypass but if it keeps the motor happy I will leave it.
SPECIAL NOTE:
This intake manifold is primarily intended for use with Vortec heads on pre-Vortec blocks. Standard engine blocks route thermostat bypass water from the block directly to the water pump through the passenger side water pump mounting flange. If the manifold is used on a 1996 and later Vortec engine that does not have the in-block bypass passage, you must route a thermostat bypass hose from the water bypass port on the front of the manifold to the 5/8” hose nipple on the passenger side of the Vortec water pump.
Use a 3/8” pipe to 5/8” hose nipple fitting, and a 7” length of 5/8” hose to accomplish this. If your engine block has the thermostat bypass passage, use the 3/8” NPT plug supplied in the kit to plug the bypass port in the front of the intake manifold.
Thermostat Bypass - you can accomplish the same thing by drilling a few 1/8" holes in the flange of your thermostat.
The way you have it right now, you are bypassing WAY TOO MUCH coolant.
Thermostats & Restrictors
We strongly recommend NEVER using a restrictor: they decrease coolant flow and ultimately inhibit cooling.
For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses.
Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM.
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it."
That thermostat is the same as the Mr. Gasket one. Worked great for me until the outside temp fell below 75 then the same **** head gets super hot until the thermostat. Finally opens.
He did 4 holes I tried 2 1/8" holes and did nothing to help. Right now everything is acting 100% normal and the head and manifold are the same temp and hold steady at a perfect 180 per the thermostat. Warms up to 210 while idle until he fan kicks on and stays at 210 until I move just like ii did with the old pump. Interestingly enough 4 1/8" holes have far more cross section area than my bypass. Looking at their description 3 x 3/16 holes would also have a far greater cross sectional area than my bypass (5/16 hose).
Eventually I am going to pop the pump again and check the built in bypass hole. But unless you can give me a good reason why it flows way too much vs the holes you mentioned with more area I am going to stick with this vs pulling the housing again and drilling my stat again. I am very curious what the difference is maybe in GPM or something similar and why it being way to much is hazardous.
But unless you can give me a good reason why it flows way too much vs the holes you mentioned with more area I am going to stick with this vs pulling the housing again and drilling my stat again. I am very curious what the difference is maybe in GPM or something similar and why it being way to much is hazardous.
From you picture, I assumed that it was 5/8" hose. Your 5/16" hose would be about perfect (as you see). With too much coolant bypassed, the thermostat is basically disabled (will never open). Not hazardous, though.
I should be more clear the bypass is not really bypassing the thermostat it is actually taking the same path as a heater core which the previous owner removed. So think of it as a very short heater core line.
Really it is helping circulation in the block before the thermostat opens and the radiator is in play
Thanks i appricate it This problem was driving me insane I'm so glad to be able to drive my Trans Am some more and get back to tuning it with the wife band
What I am hoping is one last update.
I put a regular stant 180° F thermostat back in, put my "heavy duty" water pump back on and cleaned up the bypass still using 5/16 hose. Car runs great sits at exactly 180 while cruising and then stays at about 210 when the fan comes on. Happy I can stop messing with it.
What I am hoping is one last update.
I put a regular stant 180° F thermostat back in, put my "heavy duty" water pump back on and cleaned up the bypass still using 5/16 hose. Car runs great sits at exactly 180 while cruising and then stays at about 210 when the fan comes on. Happy I can stop messing with it.
Tell me more about your power steering bracket, please.
I think that is the one I'm looking for.
05-17-2017, 08:12 AM
