302 SBF Dart block potential cooling system issue

[Todd Gross]

I have a Stock customer that I upgraded his engine over the winter and changed out his filled OEM 302 block with a Dart SHP block. It dynoed fine and all looked well, but recently he has been noticing on his data log that as the car goes down the track the cooling system temperature continually drops. It starts in the range of 120f, drops down to say 70f, then on deceleration goes back up to the 120 range. It appears to be building a vapor pocket. The bad thing is this caused the rings to butt on the forward cylinders causing damage. After tearing down to repair the ring issue we checked over the heads, gaskets and so on. We went to great lenghts to verify all the air was bled out and the water pump was functioning properly. The temp still goes down during the run. It utilizes a 35GPM Electric Water Pump ( std direction flow ) and uses water w / Purple Ice additive.
I spoke with Dart and they had not run into this.
Everything on this engine is the same as what it was on the previous block with zero issues last season.

Anybody been down this road?

Thanks-
T. Gross / JPE Inc

[V M Kauffman]

On small block Fords you should run a across over tube on the back of the intake put a tee in middle of tube or hose with a cap on it. These Ford have a bad habit of trapping air in the cylinder heads. Most intake have bosses you can drill and tap for fittings. After filling cooling system always bleed air at that point. FE's included.

[Jeff Blanchard]

I have been told that it can be very difficult to get the air out of the system, and the siamesesed cylinders of the Dart block make it even more of a problem. Is using a radiator fill funnel enough to deal with it? I am surprised more people have not responded to this post, having seen a similar situation.

[Maverick]

Curious, does the block and heads have steam holes, do you run a alternator? Just don't trust electric instruments, when strange things are going on.

[Maverick]

And where is the temp sensor located?

[Todd Gross]

Originally Posted by Maverick

Curious, does the block and heads have steam holes, do you run a alternator? Just don't trust electric instruments, when strange things are going on.

Yes the Dart Block has steam holes in the same location as the OEM block. I used Cometic head gaskets where the previous were Fel Pro. Both Head Gaskets have the steam holes and passages in the same, and I would say, proper locations.
The sensor was in the left front corner of the intake manifold. For a test we moved it to the left rear corner of the intake. It does not have a coolant cross over in the rear, but was in the coolant passage. No difference in the data log.
Yes on the alternator.

[Mike Taylor 3601]

Don't want to insult anyone with a question like this,but haven't seen it mentioned, the head gaskets are marked front and they are on correct?? doesn't have belt driven water pump of some sort rotating wrong direction?
Just mentioning some basics hadn't seen mentioned.
electric style gauge readings can be screwy sometimes,have seen sealer on threads of sensor cause bad ground for sending unit and read incorrect or not at all.
Mike Taylor 3601

[Todd Gross]

Originally Posted by Mike Taylor 3601

Don't want to insult anyone with a question like this,but haven't seen it mentioned, the head gaskets are marked front and they are on correct?? doesn't have belt driven water pump of some sort rotating wrong direction?
Just mentioning some basics hadn't seen mentioned.
electric style gauge readings can be screwy sometimes,have seen sealer on threads of sensor cause bad ground for sending unit and read incorrect or not at all.
Mike Taylor 3601

Hi Mike,
The gaskets are on correctly. No insult taken.
The water pump is a Pro-Form Electric. The owner is going to try swapping a Meziere pump off his other car, as well as removing a medium size restricer from the T-State housing and test.
As for the sensor, we are referring to a 3 wire sensor for the Holley EFI data log. We have tried another sensor with same result to rule that out.
Also have found out that the car had a puke tank for the Radiator and he changed that out to a recovery tank. Once I hear results of testing after these changes I will update post.

Thanks- T Gross

[Todd Gross]

Update*
Customer tested last night. No problems. Monitored during multiple runs.
Although 3 things were changed, I believe the addition of the recovery tank was the helper here.
It appears that the Siamese cylinders of the Dart block is not as forgiving when it comes to moving air pockets that were introduced after cool off.