This is according to the study summarized below which is an SAE paper. A key practical question is whether your valves would benefit from more detergents than are already in the gas you are using. Another question is if the cost of the additives are justified by their possible benefits.
http://www.sae.org/technical/papers/922265
"Title: Mechanism of Intake Valve Deposit Formation Part Iii: Effects of Gasoline Quality
Document Number: 922265
Author(s):
Katsuyuki Ohsawa - Toyota Central R&D Labs., Inc.
Yoshihiro Nomura - Toyota Central R&D Labs., Inc.
Hiroshi Moritani - Toyota Central R&D Labs., Inc.
Masanori Okada - Toyota Motor Corp.
Makoto Kato - Toyota Motor Corp.
Masahiko Nakada - Toyota Motor Corp.
Abstract:
Quality control of gasoline constitutents and its effect on the intake valve deposits (IVD) has become a recent issue.
In this paper, the effects of gasoline and oil quality on intake valve deposits were investigated using an intake valve deposit test bench and a sludge simulator.
The deposit formation from the gasoline maximized at an intake valve temperature of approximately 160\mDC, and the deposits formed from the engine oil were maximum at approximately 250\mDC. Therefore, the contribution of the gasoline or the engine oil appears to depend on the engine conditions.
The gasoline which contains MTBE or ethanol with no detergent additive slightly increases the deposition amount. The gasoline with a superior detergent significantly decreases the deposition amount even when MTBE or ethanol is blended in the gasoline.
Appropriate detergent fuel additive retards the oil deterioration. The deterioration degree of the oil in the engine and in the sludge simulator have a good correlation with the amount of deposition formed in the intake valve deposit test bench."
http://www.sae.org/technical/papers/922265
"Title: Mechanism of Intake Valve Deposit Formation Part Iii: Effects of Gasoline Quality
Document Number: 922265
Author(s):
Katsuyuki Ohsawa - Toyota Central R&D Labs., Inc.
Yoshihiro Nomura - Toyota Central R&D Labs., Inc.
Hiroshi Moritani - Toyota Central R&D Labs., Inc.
Masanori Okada - Toyota Motor Corp.
Makoto Kato - Toyota Motor Corp.
Masahiko Nakada - Toyota Motor Corp.
Abstract:
Quality control of gasoline constitutents and its effect on the intake valve deposits (IVD) has become a recent issue.
In this paper, the effects of gasoline and oil quality on intake valve deposits were investigated using an intake valve deposit test bench and a sludge simulator.
The deposit formation from the gasoline maximized at an intake valve temperature of approximately 160\mDC, and the deposits formed from the engine oil were maximum at approximately 250\mDC. Therefore, the contribution of the gasoline or the engine oil appears to depend on the engine conditions.
The gasoline which contains MTBE or ethanol with no detergent additive slightly increases the deposition amount. The gasoline with a superior detergent significantly decreases the deposition amount even when MTBE or ethanol is blended in the gasoline.
Appropriate detergent fuel additive retards the oil deterioration. The deterioration degree of the oil in the engine and in the sludge simulator have a good correlation with the amount of deposition formed in the intake valve deposit test bench."
