Fluctuating Water Temp on New Engine - Chevelle Tech
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post #1 of 18 (permalink) Old Feb 15th, 18, 4:19 PM Thread Starter
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Kyle
 
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Fluctuating Water Temp on New Engine

Hello Everyone!

I am a new member so please forgive me if I am not posting this in the correct section. I did post an introductory message in the welcome section. I recently installed a brand new small block 400 (Blueprint engines, 470 hp) along with a new TCI TH350. Since installing the engine, I have noticed that my water temp gauge consistently fluctuates when the engine is warm and at operating temperature. To be clear, the water temp will fluctuate from around 185 and then rapidly go down to around 150. This cycle repeats itself over and over again. In my opinion, the engine should hold a steady water temp once it is warm and the thermostat has opened. Here are some relevant details:

Thermostat is a 180 degree high flow (summit racing brand). I have tried 3 different thermostats and they all have more or less behaved the same way. I even tried an expensive Stewart/EMP 180 thermostat.

I am using a Proform (probably wouldnít have been my choice, but it was bought for me at Christmas) aluminum high flow water pump.

I have a brand new aluminum 3 row radiator (summit racing brand).

The water temperature gauge is a mechanical one that is located at the front port on the intake manifold, next to the thermostat. This gauge worked accurate and well on the previous engine I had so I doubt it would be defective.

What can cause this type of issue? Is it possible the water pump is no good? I have burped the coolant system each time I have changed out thermostats (I leave the cap off until water temp reaches 180 and thermostat opens). Maybe this is a problem related to small block 400ís? My last engine was a 383 and never did this.

Any guidance would be greatly appreciated!! Thank you!
Kyle
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post #2 of 18 (permalink) Old Feb 15th, 18, 4:57 PM
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Eric
 
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Re: Fluctuating Water Temp on New Engine

Sounds like there is air in your cooling system. I usually leave the cap off with the engine idling, when the thermostat opens I stuff a water hose into the neck at a slow trickle to force the pocket out.

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post #3 of 18 (permalink) Old Feb 15th, 18, 5:01 PM
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John
 
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Re: Fluctuating Water Temp on New Engine

I would ditch the 'High flow racing' stuff and try just a plain old regular 180į t-stat with 1/8 hole drilled in it to allow air to be purged out.

John

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Instructions...All I need is the exploded view.
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post #4 of 18 (permalink) Old Feb 15th, 18, 6:09 PM Thread Starter
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Kyle
 
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Re: Fluctuating Water Temp on New Engine

Thanks for the guidance! I thought this could be a symptom of air in the system, but I have never had any issue doing the method that I always have. I suppose it is possible there may be some air in the system so Iíll re-evaluate this. Thanks again for the help!
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post #5 of 18 (permalink) Old Feb 15th, 18, 6:15 PM Thread Starter
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Kyle
 
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Re: Fluctuating Water Temp on New Engine

Quote:
Originally Posted by Enganeer View Post
I would ditch the 'High flow racing' stuff and try just a plain old regular 180į t-stat with 1/8 hole drilled in it to allow air to be purged out.
This is kind of what I have been thinking. My last engine had a good old Chevrolet 180 degree thermostat. Never had any issue with it; however, I figured it would be good to match a high flow water pump with a high flow thermostat. I have heard multiple people state that drilling a 1/8Ē hole can solve the problem. Is the hole supposed to be drilled on the bottom base part? The thermostat that is installed on the engine right now does have a bypass valve that is supposedly a method to purge air out. This would seem to be a logical next step...Iím just tired of making coolant messes lol! I have been very careful to not get coolant on my brand new engine since Iím picky about that stuff. Thanks so much for your help!!
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post #6 of 18 (permalink) Old Feb 15th, 18, 6:15 PM
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jeff
 
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Re: Fluctuating Water Temp on New Engine

Do as John said drill a hole in the outer washer portion of the thermostat or 2 holes.
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post #7 of 18 (permalink) Old Feb 15th, 18, 6:32 PM Thread Starter
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Kyle
 
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Re: Fluctuating Water Temp on New Engine

Quote:
Originally Posted by jeff swisher View Post
Do as John said drill a hole in the outer washer portion of the thermostat or 2 holes.
This seems like the next logical step. Should I just use a standard flow Chevrolet performance thermostat (and drill the hole) or keep my existing thermostat and drill a 1/8Ē hole in it? I wasnít sure if it was advisable to use a standard flow thermostat with a high flow water pump. Thank you!
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post #8 of 18 (permalink) Old Feb 15th, 18, 9:51 PM
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Re: Fluctuating Water Temp on New Engine

Hi flow stats usually have holes in them, maybe it's not moving smooth. Put it in a pan of water on the stove & check it.
Never have believed the air thing, once the stat opens it's gone, unless you're getting combustion in the cooling system.
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post #9 of 18 (permalink) Old Feb 15th, 18, 9:55 PM
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jeff
 
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Re: Fluctuating Water Temp on New Engine

Here is what I do.
I take all the thermostats you have and place them in a pan of water and turn the heat on under them and watch the temp and watch them as they open.

Many 180 thermostats I checked began to just crack open at 180. full open about 195 and the 195's began to open at 195 and full open about 205.
You can then reduce the heat an watch them close.. if one slams shut right at a cool down point vs slowly closing I would not use that one.

They should gradually open and gradually shut.
The odd thing is the 160 thermostats I checked were full open at 160.

I cook all thermostats in water before installing them.

Some say do not run without a thermostat but I have done it many times but i put a restrictor in where the thermostat goes.
Sometimes that restrictor is a thermostat with the middle guts removed.

special circumstances some had double pass or triple pass radiators.

You could put 2 1/8" holes.. 1 hole does not make me feel warm and fuzzy. but it will allow you to fill the radiator up cold and not need to burp it.

It will take longer for the thermostat to open the more holes you drill into it.
That is because the holes allow coolant to circualte and this cools the engine enough that it takes longer to get to operating temp.

I feel this is a bonus as I feel an engine needs to slowly warm up especially aluminum head iron block..something in my mind thinks there would be less head gasked scrubbing in a deal like that.
I may be off base on that.
I just know what has worked for me and I have been drilling multiple holes in thermostats for 30 years. without issues.

A draw back would be short trips ( I do not do short trips).
The short trip may not get the fluids up to temp and you could see added wear from condensation in the oil.
Or if you got on the loud pedal with a cold engine you could see issues.

I like to get them up to temp.. But realize oil temp and coolant temp are different things.
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post #10 of 18 (permalink) Old Feb 15th, 18, 9:56 PM
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Re: Fluctuating Water Temp on New Engine

I am a slow typer beat me to it Jim
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post #11 of 18 (permalink) Old Feb 15th, 18, 9:57 PM
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Re: Fluctuating Water Temp on New Engine

As much as the stuff was a nice thought for a Christmas present, it sounds like it's not really matched to the application you want in the engine. i.e. nice steady temp around 180. You will have plenty of cooling capability with the stock t-stat, water pump and aluminum radiator.

Swap out both for regular off the shelf t-stat (drill a hole in the flat washer part) and stock water pump, put the high flow water pump on the shelf for just in case or trade to another car guy if the stock setup works.

We all have gone off the deep end one time or the other looking at performance parts and had to wade back to having something that works for our true use.
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John

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Instructions...All I need is the exploded view.
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post #12 of 18 (permalink) Old Feb 15th, 18, 11:02 PM Thread Starter
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Kyle
 
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Re: Fluctuating Water Temp on New Engine

This is all excellent information to have; thanks guys!! I would like to exhaust all options with the thermostat before thinking about installing a different water pump. I do agree that a standard flow water pump/thermostat combined with the aluminum radiator would have performed plenty well. I will try drilling two 1/8Ē holes in the thermostat and testing this combination. The thermostat that is currently installed does have a little bypass valve that I figured would be sufficient to purge any air out. Also would make sense to test thermostat in a pot to verify it is performing correctly. Unfortunately, quality with any parts can be hit or miss these days. That can be really frustrating when trying to diagnose problems like these. Once again, thanks for all of the great advice!
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post #13 of 18 (permalink) Old Feb 21st, 18, 1:18 PM
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Re: Fluctuating Water Temp on New Engine

Another Trick to make sure you get any/all Air out of the Cooling System
is to Elevate the Front of the Car when you change/adjust the Coolant Level etc.

Leave Rad Cap off while Engine warms up and the Thermostat Opens up
to see if there is a good Flow of Coolant from Engine into Rad
by looking into the open Rad Cap Hole
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post #14 of 18 (permalink) Old Feb 21st, 18, 1:56 PM
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Re: Fluctuating Water Temp on New Engine

Probably not related to the issue you are having, but since you have a SB400 with cooling issues I have to ask; did you rebuild it yourself? If so, did you make sure the heads have the 400-required steam holes and did you use the correct head gaskets for a 400?
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post #15 of 18 (permalink) Old Feb 21st, 18, 2:15 PM Thread Starter
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Kyle
 
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Re: Fluctuating Water Temp on New Engine

Quote:
Originally Posted by Rich-L79 View Post
Probably not related to the issue you are having, but since you have a SB400 with cooling issues I have to ask; did you rebuild it yourself? If so, did you make sure the heads have the 400-required steam holes and did you use the correct head gaskets for a 400?
This engine was built by Blueprint Engines. They actually use a brand new block that they build (not a GM 400 block). It supposedly has some neat aftermarket features such as priority main oiling, 4 bolt main-splayed caps, and 1 piece rear main seal. Your thoughts have definitively crossed my mind, though! I have been wondering about that as well, but I would assume they would have drilled steam holes in the cylinder heads because of the siamese cylinder bores. Iíll cross my fingers that itís something simple. I havenít had a chance to diagnose anything further yet.
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