New 350 overheating during break-in

[Slonaker]

I just got my new 350 crate motor (Chevy universal 350 #10067353) installed and running. It started up easily, and ran pretty good considering that nothing had been adjusted yet. There were no odd smells or noises. Just the usual smell of paint cooking off of stuff.

In less than 5 minutes, the temperature, as indicated, was at 210. I shut it down. I messed with the timing (several times), tried it with and without the advanced hooked up, and ran it with and without a thermostat. None of it made a diference. It always indicated it was running really hot even though t was about 50 degrees outside.

The old 305 was okay with this radiator, fan, water pump, etc. They are all relatively new except for the fan clutch. It has new belts and hoses.

The odd thing is that it did not feel hot or smell hot. I could grab and hold the upper radiator hose even when it said it was overheating.

I installed a mechanical gauge I had laying around in the water neck, and it didn't even move the needle. I also dunked the bulb in a pot of boiling water, and it moved very slowly upt to about 150 degrees and sat there. I don't trust it now, so that was no help. I may end up buying another one tonight to see what happens.

I'm wondering if it is really overheating, or if I have a sending unit that is incompatible with my gauge. The hole in the head for the sending unit is a different size fro the one for my 305.

Sallee Chevrolet, on their website,says "Temperature Sender-Vehicles from 1979 and up will require a temperature sending adapter P/N 00444034 which Sallee Chevrolet can supply you with if needed. The sender is located on the driver side of the engine and has a green wire going to it." I went to my local dealer, but the lady at the parts counter said it was a bad part number. It apparently is since it does not show up on the websites for any of the Chevy dealers, including Sallee Chevrolet where I got it from.

I ended up just going to a regular auto parts store and buying a sending unit from a 78 Chevy pickup. Could it be that it is not compatible with my gauge? Has anyone else come across this problem? Did you use a different sender, or an adapter?

Can anyone think of anything else that might be causing it to overheat?

Slonaker

[dznucks]

i encountered the same situation when i replaced my 305 with a crate 350.
typically, from my experience, a new motor will heat up unusually the first time or two its is borught up to operating temp. the 350 should be able to handle up to around 270-290 deg before you have messed something up.

but in my case, since it was the first time i was cranking the crate motor i had not completely installed the front clip in case i had overlooked something and needed to repull the motor. my motor kept jumping straight up to 300 deg, so i changed out thermostats, checked the radiator, even plugged a water hose straight into my radiator flush lines. nothing. so i had an old mechanics come help. he took one look and said it was the fan shroud. sure enough i put on the fan shroud and it ran fine. .

good luck

[Slonaker]

My fan shroud is installed.

I, too, have heard about engines getting a little hot during break-in. I have a lot of time and money in this, and the temp scares me. It scares me a LOT.

Slonaker

[Jonboy]

I would make sure that you have the correct sending unit. It is also possible you have an air bubble in the cooling system. Let it run with the radiator cap off, and see what happens.

[bodydropped]

check ur water pump u might have the wrong one

[Slonaker]

I was running it with the radiator cap off. I don't know if the new sending unit is compatible, but the old one won't fit into the head.

The water pump was one I bought new for the 305, and it has about 5K miles on it. It was working well on the 305, even running the A/C with outside temps near 100 degrees. It should be able to cool the truck at 50 degree outside temps. I can see water droplets coming from the radiator neck, so I believe it to be pumping well.

Thanks for the suggestions. Any more? Does anybody know if the sending unit I have is compatible with my gauge, or whereto get an adapter for the old one?

Slonaker

[Jim85IROC]

WHen I ran the new motor I built for my IROC, it ran real hot the first time. My timing was way off, which no doubt had a lot to do with it, but remember that a new motor will have very tight tolerances and there will be a lot more friction until all of the metal surfaces seat.

[Slonaker]

Originally Posted by Jim85IROC

WHen I ran the new motor I built for my IROC, it ran real hot the first time. My timing was way off, which no doubt had a lot to do with it, but remember that a new motor will have very tight tolerances and there will be a lot more friction until all of the metal surfaces seat.

How hot did it get, and how long did it run hot?

Slonaker

[454HO]

Is it overheating at idle, or are you running it up around 2500rpm to break in the cam?

Check your spark plugs to see if they look like they have overheated too. What is your fuel mixture like, rich or lean? Is this running an old carb or new?

What do you have for exhaust? Manifolds and small pipes are more restrictive than headers and large pipes.

Do you have a box fan or shop fan you can set in front of the truck to blow air toward the radiator?

The temp sending unit is nothing more than a thermistor. That is a resistor that changes resistance with temperature. As the temperature goes up, the resistance goes down. It should look something like the chart in this spec sheet. http://www.pe-ltd.com/downloads/coolant_temp.pdf

[Slonaker]

Originally Posted by 454HO

Is it overheating at idle, or are you running it up around 2500rpm to break in the cam?

Check your spark plugs to see if they look like they have overheated too. What is your fuel mixture like, rich or lean? Is this running an old carb or new?

What do you have for exhaust? Manifolds and small pipes are more restrictive than headers and large pipes.

Do you have a box fan or shop fan you can set in front of the truck to blow air toward the radiator?

The temp sending unit is nothing more than a thermistor. That is a resistor that changes resistance with temperature. As the temperature goes up, the resistance goes down. It should look something like the chart in this spec sheet. http://www.pe-ltd.com/downloads/coolant_temp.pdf

This is while attempting to break in the cam. I hate starting and stopping it during the process.

I have manifolds. Manifolds are more restrictive than headers, but there is no reason why manifolds with dual 2 1/4 pipes should be unable to flow sufficiently for a stock 350 during break-in on a 50 degree day. They certainly would not make a cold engine overheat after 3 to 4 minutes of running. The entire exhaust sytem worked fine for the 305, so I have no reason to believe there is anything to prevent it from working here.

Nope, no box fan setup. Again, it should not be becessary on a 50 degree day. The whole cooling setup is relatively new, upgraded from a 2 row radiator to a 3 row, and was functioning well with the 305. I can set up a fan, though, since I have one. It can't hurt.

It is running on the old quadrajet from the 305. That is all I have. I have no idea if it is rich or lean. I was doing this last night by myself, and only ran it about 5 minutes total. It heated up really fast, which does not allow time to figure out what is going on

What does a plug look like if it overheats?

Slonaker

[mhicks]

I think you need to go and buy a new temp gauge with the sending unit that goes with it and that way you will know if it is overheating or not. It is not good to turn it of and on while trying to break it in.

[Slonaker]

I'm leaving work now to do just that. I was hoping someone knew about the sending units, but this should clear up the doubts about whether or not it is actually overheating. I will at least then be able to decide if my problem is the sender or something else.

Slonaker

[jermasaurus]

I had the same deal with the sending unit not fitting the head, so i used the one in the 350's head. Thought it was overheating. It never pegged the gauge, but just indicated very hot. So I got an adapter to use the old sender and it read correctly.

You most likely need the other sender and an adapter to make it fit.

-Jeremy

[Slonaker]

Originally Posted by jermasaurus

I had the same deal with the sending unit not fitting the head, so i used the one in the 350's head. Thought it was overheating. It never pegged the gauge, but just indicated very hot. So I got an adapter to use the old sender and it read correctly.

You most likely need the other sender and an adapter to make it fit.

-Jeremy

That's the kind of info I am looking for. Where did you get the adapter?

Do you have a part number? I am planning to hit the auto parts stores after dinner, but I expect that to be quite an ordeal. If I can't list the application, and whether or not it had a/c and an automatic transmission, my local stores aren't much help.

Slonaker

[swervin ervin]

Go to a hardware store and get a brass fitting. I think it's 1/2" pipe thread but don't hold me to it. Also take your sending unit with you so you can get one that it will fit in to.

If my memory serves me right (don't forget I am getting old), it will be 1/2" pipe O/S with 1/4" pipe I/S. Once again, don't hold me to this. Best to take your sender with you if you can. I'm pretty sure on the 1/2" part though.

[79Silv4x4]

210 is not a problem--it took about 2-300 miles on this exact motor in my '83 before it came back down. I wouldn't worry.

[Slonaker]

I'm headed out right now to try to get an adapter.

It was at 210 and rising when I shut it off after 3 or 4 minutes. It hadn't leveled off there. That would not have worried me as much.

Slonaker

[79BIG10]

Swervin is right on the adapter. Just make sure to use the tapered fitting to hold the thermostat end in. If you don't it will leak believe me I've done this

[piecesparts]

IF in doubt as to what the real temperature is, get a simple metal thermometer with a probe on it (like the air conditioning guys use) and stick it in between the hose and the radiator inlet fitting. It will give you an idea of what the water is that is going to the core. You could borrow or buy a simple heat gauge (mechanical) to replace the one you have for nickels and dimes (compared to the motor) and install it for a short period of time and leave it on the fender well until the motor is timed and running right. My bet is on the temperature sending unit not being compatible or getting a proper ground to indicate that the temperature is right. I have put a few engines in trucks in my time and I cannot say that the running hot on the first run is a real threat, unless the temps do not level off. Remember you have to wear in the grooves in the cylinders and bearings for the motor to run smooth.
Are you sure that you have gotten all of the air out of the motor? Check the intake manifold for any trapped air. It does not matter what motor you have in the truck the sending unit has to match the dash gauge for a good reading. It does not care what it is hooked up to. What happened to the original temperature sending unit?

I'm not sure what 79BIG10 means by a tapered adapter. ALL pipe threads are tapered threads, that's what makes them Pipe threads. I'm betting that what you need is a 1/2" outside thread and a 3/8" inside thread for your adapter.

[Slonaker]

Well, I got an adapter at Lowes for a $1.58. Lets hope it holds water. At least if it leaks, that is a minor issue.

What do you mean by tapered at the thermostat end? Do you mean the male part of the adapter should be tapered rather than straight pipe thread? The one I got is not. We'll see what happens.

Thanks everyone.

Slonaker

[79BIG10]

Originally Posted by Slonaker

.

What do you mean by tapered at the thermostat end? Do you mean the male part of the adapter should be tapered rather than straight pipe thread?

I had a bushing like you did and it didn't work. The bushing going into the head has to have a catch at the end to prevent the sensor to go all the way in. Do a test fit- Before installing the bushing in the head attach it to the sensor's bushing. Then push the sensor in towards where the head would be. If it moves back and forth then it will leak. If it's tight and not moving you're fine. I had to end up using a spare one I had from a cheap temp kit from AZ.

[Slonaker]

Brandon:

I'm still not sure what you are saying, but I will definitely check it for leaks. Everything fit nice and tight, so hopefully I won't have any problems.

Well, the new sender was the problem. I installed the old sender with the adapter, and now the gauge reads acurately. It warmed up to 195 degrees during break-in, and then never went beyond it. It is actually running pretty good.

I got pulled over by the Selma PD last night when I went on my test drive. A police car that was hiding under an overpass saw me at a stop sign on the access road. He turned on his headlights, and came screaming up within 50 feet of me, then stopped. He just sat there, so after 15 seconds or so, I pulled out. He followed me up onto IH 35, and pulled me over. WTF?

Another police car showed up, and they asked me a bunch of questions about why I was out, where I came from, and where I was going. I'm sitting there looking like a hooligan on the side of the interstate, in a truck with no hood. They finally told me that my truck was an EXACT match to one seen leaving several burglaries over the weekend. Just my luck.

Thanks again to everyone who helped.

Slonaker

[C&C Chevy]

slonaker, now we know how you got that brand new crate engine!

Good to hear you got it figured out. I'd been worried too.

[TEAM THC]

I Learned Something Here Today. Things For Me To Look Out For When I Swap Out My Motor. Great Info Guys!

[84slopwaggin]

ya me too come to think of it when my wore out 350 which I thought was a305 was running my temp gauge read right around 225. I changed thermostats with nothing improving. Now with the engine out I'm figuring now it could of well been the same deal slonaker was experiecing, so I guess I can expect to experience a over heating temp gauge reading with the new motor until I match the right parts.